digital.library.unt.edu/67531/metadc705890/m2/1/high_re… · 0 were originally inaugurated in 1976...

0 were originally inaugurated in 1976 in honor of Sydney Chapman.

e permit organized and in-depth exploration of specialized subjects.

0 encourage interdisciplinary focus on special problems.

e give students a chance to interact with leaders in their field.

0 have limited attendance (125) and can be heId anywhere.

0 can be proposed by any AGU member.

0 about 5-8 conferences held each year.

Convening a Chapman can be as easy as 1, 2, 3. 1. You submit a written proposal to AGU,

2. AGU staff solicits approval of the proposal from AGU officers.

3. You handle the science; AGU staff handles the administrative duties.

For Further Information To rekeive details on convening a Chapman Conference, contact

Brenda Weaver American Geophysical Union 2000 Florida Avenue, N.W.

Washington, DC 20009 Telephone 202-939-3203

Fax 202-328-0566

ih J

COVER: The scale of processes involved in coupled hydrogeologic mass transport and a con- of modeling and testing from the atomistic- to the basin-scale. i t is now possible to test the fundamental atomic level parameterizations in the laboratory and to use field evidence of fluid flow and mass transport that defme the proiesses of flow on the large time and space scales. The next generation of hydrogeologic models must invoke both a development of grid-scale parameterizations from sound scientific principles at the atomistic level and a test of such parameterizations over t i m e and length-scales that are beyond and/or below the buckdgridscale of the computational model.

2

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

- 4 *

AGU Chapman Conference fg; Hydrogeologic Processes: Building and Testing ?I Atomistic- to Basin-Scale Models

+ERE+

June 6-9, 1994 Lincoln, New Hampshire

General Information

CONVENER

STEERING COMMITTEE

Thomas Torgersen, University of Connecticut

John Bredehoeft, U.S. Geological SUNV Steve Brown, Sandia National Laboratory Anthony Hess, Pacific Northwest Laboratory Antonio Lasaga, Yale University Thomas McEveilly, University of California-Berkeley Danny Rye, Yale University

- SITE - All scientifk sessions (oral and poster) will be held at the Mountain Club on Loon Mountain, located in the scenic White Mountains of New Hampshire. This popular winter ski resort offers ample activities to choose from year-round including mountain biking, hiking, tennis, summit Gondola rides, horseback riding, and shopping. The Mountain Club is a full service resort, with over 300 rooms and suites, and plenty of dining and evening entertainment options.

REGISTRATION - EveIyone attending this conference must register and pay the registration fee. The registration fee covers the costs of the program with abstracts, admittance to the scientific sessions, and the opening reception. The conference barbecue is a ticketed event which costs an additional $22.00. Tickets for the barbecue must be purchased by 1O:OO a.m. on Tuesday, June 7. The field trip to Mirror Lake Hydrologic Watershed Test Site will be an additional fee to cover transportation costs. The date, time, and costs of the field trip will be determined on site depending upon interest. A sign-up sheet for the conference barbecue and the field trip will be located at the registration desk. AGU accepts payment by American Express, Mastercard, or MSA credit cards, checks, and money orders. Purchase orders are not accepted.

FIELD TRIP - There will be a field trip to the Mirror Lake Hydrologic Watershed Test Site. This site, located 1/2 hour drive from Loon Mountain, is being used as a test bed for an integrated study of fluid flow in fractured media with hydrologic, geophysical, geochemical, and field geology components. Tom Torgersen (conference convener) and Paul Hsieh (USGS) will be the field trip leaders. Participants will be charged a nominal fee to cover transportation fees. Additional information will be forthcoming. A sign-up sheet is located at the registration desk.

SOCIAL EVENTS

Monday, June 6 9:30 p.m. Reception Following Opening Session

Tuesday, June 7

TBA

5:oo p.m. Group Barbecue (Ticketed Event) $22.00 Must purchase tickets by 10:OOa.m. Tuesday.

1/2 Day Field Trip to Mirror Lake Hydrological Watershed Site (nominal fee requested)

COSPONSORSHIP - AGU gratefully acknowledges ?he Department of Energy and the National Science Foundation for their cosponsorship of this conference through providing travel support.

4 A P M 4

* @ B M M +EER%+

All meetings activities will be held at the Mountain Club on Loon Mountain in the Governor A d a m Lodge

Monday. June 6. 1994 Registration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5:OO p.m. - 7:OO p.m. IntroductionTWelcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7:OO p.m. - 7:30 p.m. Invited Talks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7:30 p.m. - 9:30 p.m. Reception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3 0 p.m.

Invited Talks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8:OO a.m. - 9:00 a.m. Session I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9:00 a.m. - 9:45 am. Introduction of Poster Presenters . . . . . . . . . . . . . . . . . . . . . . 9:45 a.m. - 1O:OO a.m. Coffee Break. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1O:OO a.m. -10:30 p.m. Invited Talk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10:30 a.m. -11:OO a.m. Session I Continues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11:OO a.m. -12:15 p.m. Session II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1215 p.m. - 1:00 p.m. Break and Poster Viewing . . . . . . . . . . . . . . . . . . . . . . . . . . 1:00 p.m. - 5:OO p.m. Conference Barbecue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5:OO p.m. - 7:OO p.m. InvitedTalks .................................... 7:OOp.m. - 8:OO p.m. Session III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8:OO p.m. - 9:00 p.m. Panel-led Discussion .............................. 9100 p.m. - 1O:OO p.m.

Tuesday. June 7. 1994

Wednesday. June 8. 1994 Invited Talks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8:OO a.m. - 9:00 a.m. Session IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900 a m . - 1O:OO a.m. Coffee Break. and Poster Viewing . . . . . . . . . . . . . . . . . . . . . 1O:OO a.m. -10:30 a.m. Invited Talk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10:30 a.m. -11:OO a.m. Session IV continues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11:OO a.m. -1230 p.m. Break and Poster Viewing . . . . . . . . . . . . . . . . . . . . . . . . . . 12:30 p.m. - 7:OO p.m. Invited Talk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7:OO p.m. - 7:30 p.m. Session V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7:30 p.m. - 9:00 p.m. Panel-led Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9:00 p.m. - 1O:OO p.m.

Invited Talks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8:OO a.m. - 9:00 a.m. Session V Continues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9:00 a.m. - 9:30 am. Session VI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9:30 a.m. - 1O:OO a.m. Coffee Break and Poster Viewing . . . . . . . . . . . . . . . . . . . . . 1O:OO a.m. -10:30 a.m. Session VI Continues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10:30 a..m. -12:OO p.m. Break and Poster Viewing . . . . . . . . . . . . . . . . . . . . . . . . . . 12:OO p.m. - 7:OO p.m. Panel Summary Presentations . . . . . . . . . . . . . . . . . . . . . . . . 7:OO p.m. - 8:OO p.m. General Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R O O p.m. - 9:00 p.m. General Business and Publication Schedules . . . . . . . . . . . . . . 9:00 p.m. - 1O:OO p.m. Conference Adjourns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10:OOp.m.

Thursdav. June 9, 1994

2

- . SCIENTIFIC PROGRAM

AGU Chapman Conference on Hydrogeologic Processes: Building and Testing Atomistic- to Basin-Scale Models '@ *

c;j +&ER%+ e June 69, 1994 Lincoln, New Hampshire

Convener: Thomas Torgersen, University of Connecticut

MONDAY, JUNE 6,1994

5:OO p.m. - 7:OO p.m. Meeting Registration

7:OO p.m. Introductory Statements; Focus and Purpose, Product and Output of Meeting

7:30 p.m.

8:OO p.m.

8:30 p.m.

9:OO p.m.

9:30 p.m.

8:OO a.m.

8:30 a.m.

Session I:

9:OO a.m.

9:15 a.m.

9:30 a.m.

G. Garven

J. I. Drever

A. Nur

N. Oreskes and K. Belitz

Invited - Three Dimensional Models for Large Scale Transport and Ore Mineralization in the Midcontinent Basins, USA

Invited - Mineral Dissolution Kinetics: Experiments and Field Tests

Invited - Seismic Detection, Characterization, and Monitoring of Subsurface Fluids and Their Flow

Invited - Modeling Complex Systems: What Can Be Done?

CONFERENCE RECEPTION

TUESDAY, JUNE 7,1994

C. C. Barton

L. R. Myer, N. G. W. Cook

Pmcess to Grid Scale Parameterization

A. R. Felmy, J. R. Rustad, and D. M. Sherman

D. R. Janecky and S. Chen

D. Schulze-Makuch and D. S . Cherkauer

Invited - Scaling and Evolution of Fracture Networks and Fluid Flow in Space and Time

Invited - Void Topology and the Hydromechanical and Geophysical Properties of Fractures

Linking Quantum Mechanics, Molecular Dynamics, and Thermodynamics: Estimating the Surface Protonation of Goethite

Detailed Heterogeneous Pore Scale Models for Transport Coupled to Chemical Reactions and Multi-Phase Flow

Effects of Scale on Dispersivity and Hydraulic Conductivity Behavor in a Carbonate Aquifer

3

Introduction of Poster Presenters

1O:OO a.m. COFFEE BREAK

Invited - Geochemical Kinetics and Transport Coupling in Hydrogeologic Systems

10:30 a.m. C. I. Steefel

11:OO a.m. H. W. Stockman Estimation of Scaling Errors via Lattice Gas Automata: Application to Diffusion and Adsorption

11:15 a.m. B. Dutrow Temporal and Spatial Variations of Fracture Propagation: Fluid Pressures in Contact Metamorphic Environments

11:45 a.m.

12:OO p.m.

11:30 a.m. W. C. Shanks, 111, D. R. Janecky, and S. Y. Chen

Modeling of Fluid Flow and Mineral Reactions at Seafloor Hydrothermal Vents Using Hydrodynamical Cellular Automata

J. H. Cushman, 3. Curry Fluids in Microporous Systems

J. Wan, C.-F. Tsang, T. K. Tokunaga

Studying of Particle Transport in Saturated and Unsaturated Fractured Porous Media at Scales Down to Micrometers

Session 11:

12:15 a.m.

12:30 p.m.

Inferring Process

Water Circulation in Metamorphism D. Rumble, 111

M. Musgrove and J. L. Banner

Geochemical Evidence for the Origin, Evolution, and Flowpaths of Saline Groundwaters in a Regional Flow System: Midcontinent, USA

12:45 p.m. T. C. Omtott, H.-Y. TSeng, G. Gao, R. C. Burruss, and D. S. Miller

Coupling Hydrothermal Fluid Flow to Thermal Maturity for a Triassic Basin Using Fluid Inclusions and Fission Track Length Distributions

1:OO p.m. BREAK and Poster Viewing

5:OO p.m.

Invized - Space-Time Variation of Hydrologic Parameters Considering Scale and Information Content

7:OO p.m. S. P. Neuman

7:30 p.m. A. C. Hess Invited - The Involvement of Modern Theoretical Methods to Study Atomic Scale Phenomena of Geochemical Importance

4

- session 111:

8:OO p.m.

8:15 p.m.

8:30 p.m.

8:45 p.m.

9:OO p.m.

8:OO a.m.

8:30 a.m.

Session Iv:

9:OO a.m.

9:15 a.m.

9:30 a.m.

9:45 a.m.

1O:OO a.m.

10:30 a.m.

11:OO a.m.

Laboiutory Tests of Pammeterizations

W. B. Durham, B. P. Bonner, and S. R. Brown

T. K. Tokunaga, S. R. Sutton, and S. Sajt

D. A. Lmkner, D. E. Moore, and J. D. Byerlee

w. zhu

Panel-led Discussion

Measurement and Simulation of Fluid Flow in Real Fractures: A Reality Check

Reduction and Diffusion of Selenium in Soil Aggregates: Synchrotron X-ray Fluorescence Microprobe Studies of Intra-aggregate Chemical Heterogeneity Formation

Rate of Permeability Reduction in Granite at Elevated Temperatures

Percolation Modeling of Permeability Evolution During Hydrothermal Compaction

WEDNFBDAY, JUNES, 1994

A. C. Lasaga, J. Mer, J. Ganor, T. Burch, and K. Nagy

Invited - Ab-Initio Models, Water-Rock Kinetics and Coupled Hydrogeochemical Processes: Global Implications of Atomic Phenomena

J. H. Cushman and T . R. Invited - Scaling and Transport in Systems Ginn With Continuously Evolving Heterogeneity

&id and Large Scale ‘Defemination‘ of Pameters

R. L. Madcie

G. Teutsch

Can Electrical Geophysical Measurements Tell Us Anything About Fluids in the Subsurface?

Effective Hydraulic and Transport Parameters From Laboratory- and Field-Scale Measurements: A Method Inter-Comparison Study

R. Nadeau, T. V. McEvilly, and W. Foxdl

X. M. Zhao, M. N. Toksbz, and C. H. Cheng

COFFEE BREAK and Poster Viewing

D. R. Veblen

Microearthquake Clustering and the Slip Process on the San Andreas Fault at Parkfield, California

Stoneley Wave Propagation Across Borehole Permeability Heterogeneities

Invited - Atomistic View of Low-Temperature Fluid-Mineral Reactions: Chemistry, Reaction Mechanisms, Diffusion, and Kinetics

K. Belitz and J. D. Bredehoeft

5

Basin-Scale Permeability: Examples From Three North American Basins

11: is a.m.

11:30 a.m.

11:45 a.m.

12:OO p.m.

12:15 p.m.

12:30 p.m.

7:OO p.m.

Session V:

7:30 p.m.

7:45 p.m.

8:OO p.m.

8:15 p.m.

8:30 p.m.

8:45 p.m.

9:OO p.m.

H. Lewis and G. D. Couples

S. Rojstaczer and S. Hickman

J. C. S. Long, C. Doughty, and K. Hestir

L. P. Baumgartner, M. L. Gerdes, G. T. Roselle, and M. A. Person

P. 0. Koons, P. Upton, D. Craw, and C. P. Chamberlain

BREAK and Poster Viewing

J. J. Ague

Hot Mineraking Brines in a Thin Irish Basin - - Results of Simulating the Fluid-Flow System, and Lessons About Modelling

In-Situ Study of Physical Mechanisms for Permeability Changes Associated With the 1989 Lorna Prieta Earthquake

Methods for Coupling Information About the Genesis of Geologic Features to the Development of Hydrologic Models

Effect of Mineral Reactions on Porosity and Permeability Development in Contact Aureoles

Geochemical and Model Observations on Thermal, Topographic and Mechanical Components of Fluid Flow in the Southern Alps

Invited - Fracture-Controlled Fluid Flow and Mass Transport in the Middle and Lower Crust

Applimiions of Grid Scale Parameters in MacmMo&ls

C. W. Gable, G. Zyvoloski, and B. Robinson

S. L. Brantley

M. Person, D. Toupin, P. Eadington, and D. Warner

S. D. Sevougian, S. B. Yabusaki, C. I. Steefel, and T. D. Scheibe

s. Ge

G. D. Couples, R. S. Haszeldine, D. Darby, C. G. Fleming, H. Lewis, C. McKeown, and R. N. T. Stewart

Panel-led Discussion 6

Integration of Hydrostratigraphic Data in Reactive Transport Models

Is It Possible to Use Mineral-Water Reaction Rates From Laboratory Measurements to Quantify Chemical Evolution in Natural Systems?

Tracing Active and Ancient Groundwater Flow Systems Across the Cooper & Eromanga Basins, Australia, Using Mathematical Modeling and Geothermal Data

Multicomponent Reactive Solute Transport in Physically and Chemically Heterogeneous Aquifers

Basin Scale Modeling of Coupled Hydrogeological and Mechanical Processes

Importance of Geometry in Simulating Groundwater Systems - Examples From Hydrocarbon Exploitation, Minerals Genesis, and Environmental Protection

THURSDAY, JUNE 9,1994

8:OO a.m.

8:30 a.m.

9:OO a.m.

9:15 a.m.

Session VI:

9:30 a.m.

9:45 a.m.

1O:OO a.m.

10:30 a.m.

10:45 a.m.

11:OO a.m.

11:15 a.m.

11:30 a.m.

12:oO p.m.

7:OO p.m.

8:oO p.m.

9:OO p.m.

1O:OO p.m.

S. R. Brown

P. A. Hsieh, A. M. Shapiro, D. J. Goode, and C. Tiedeman

S. E. Ingebritsen and D. 0. Hayba

D. 0, Hayba and S. E. Ingebritsen

Scaling Relations

T. R. Ginn, C. S. Simmons, B. D. Wood, and E. M. Murphy

T. D. Scheibe and S. B. Y abusaki

COFFEE BREAK and Poster Viewing

A. F. B. Tompson, A. Schafer-Perini, and R. W. Smith

J. F. Peters and S. E. Howington

P. Gavrilenko and Y. Gueguen

R. Beckie

S. Follin

BREAK and Poster Viewing

Panel Summary Presentations

General Discussion

General Business and Publication Schedules

Conference Adjourns

Invited - Transport Properties of Single Fractures

Invited - Hydraulic Conductivity of Fractured Crystalline Rocks From Meter to Kilometer Scale: Observations From the Mirror Lake Site, New Hampshire

Fluid Flow and Transport Near the Critical Point of H,O

Hydrologic Modeling of Magmatic- Hydrothermal Systems

Stochastic Convective Transport With Nonlinear Bioreaction in Heterogeneous Media

Permeability Scaling in a Numerical Aquifer

Simulation of Reactive Contaminant Migration in Physically and Chemically Heterogeneous Soils

Development of Scale-Invariant Transport Laws for Groundwater Remediation Modeling

Fluid Overpressures and Hydrological Properties of the Earth Crust

Universality and Models of Groundwater Flow

A Note on Supra-Grid Modeling of Groundwater Flow Through Crystalline Rocks

7

POSTER PRESENTERS:

V. J. Homer, P. M. Jardine, and R. J. Luxmoore

Scaling Up in Percolation Modelling for Fluid/Solute Transport

C. G. Fleming, G. D. Couples, and R. S . Haszeldine

P. T. Dougan, G. D. Couples, M. W. Frye, and H. R. Lane

D. Darby, R. S. Haszeldine, C. G. Fleming, and G. D. Couples

G. R. Moline

J. A. Yeakley, G. M. Hornberger, J, L. Meyer, and W. T. Swank

C. McKeown, R. S. Haszeldine, and G. D. Couples

L. A. Scott and K. BeIir

M. J. Brown, K. Belitz, and N. Oreskes

J.K. Sueker

The Thermal Effects of Fluid Flow Within the Central Graben: A Finite Element Model

Implications of the Biothem Approach (Biostratigraphic Analysis) to Large-Scale Hydrogeologic Simulations

Analysis of the Overpressured Central Graben, North Sea via Linked Regional Potentiometric Mapping and Pressure Modelling

Core- to Basin-Scale Parameterization: Bridging the Gap Through Electrofacies Classification

Multi-Scale Parameterization of a Hillslope Hydrology Model for Soil Water Content and Flux Estimates on Climate Time-Scales

The Role of Groundwater Models in Locating a Safe Site for Britain's First Radioactive Waste Repository

The Effect of Geologic Complexity on Groundwater-Flow, a Case Study of a Glacial Esker Deposit

Hydrostratigraphy and Paleotopography of Carboniferous Ireland: Framework for Hydrologic Modeling of the Carboniferous Carbonate-Hosted Zn-Pb Deposits of Ireland

Flowpath Determination for Four Alpine/Subalpine Watersheds in Rocky Mountain National Park, Colorado

DISCLAMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracj', completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

8

"+REJ&' Monday, June 6, 1994

Evening: INTRODUCTION

Three Dimensional Models for Large ScaleTransport and Ore Mineralization in the Midcontinent Basins, USA

Grant Garven (Department of Earth and Planetary Sciences, The Johns Hopkins University. Baltimore, Maryland 21218)

Sedimentary basins of the USA Midcontinent region contain large geothermal and petroleum reservoirs and huge stratabound Pb-Zn-Ba-F ore deposits of the Mississippi Valley type (MVT) that appear to have origins related to ancient migration of deep groundwater. I describe here a new finite dement model for simulating coupled groundwater flow and heat transport in a three dimensional framework. This type of model is needed especially for assessing the paleohydrogeology in the Midcontinent where a number of mountain building events controlled the transient evolution of regional flow throughout the Phanerozoic (Garven et al., 1993). We have compared two numerical approaches to solving the three dimensional basin problem: (1) Slice successive over- relaxation (Huyakom et al., 1986) and (2) Preconditioned conjugate gradient using the ORTHOMIN method (Mendoza et ai., 1992). Althoughboth approaches can be applied to models of basin hydrology, the latter method is superior in its ability to deal with extreme heterogeneity, anisotropy, and storage requirements for the large number of elements required for modeling complex sedimentary basins. Three dimensional effects of basement relief, land surface topography, and geologic heterogeneity are discussed and illustrated with simulations of transport at a basin scale.

Realistic models for ore mineral'mtion and mass transport at the district and deposit scale require coupled simulations that rigorously simulate reactive flow in nonisothermal environments. Examples of geochemical reactive flow simulations are presented here to illustrate the recent finite element techniques developed by Raffensperger and Garven (1994). Three conceptual geochemical models for MVT ore deposition are tested with the coupled model for comparison purposes.

Mineral Dissolution Kinetics: Experiments and Field Tests

J I Drwer@epartment of Geology & Geophysics, University of Wyoming, Laramie. WY 82071-3006; ph. 307-766-6434; fax 307-766-6679; Internet: [email protected])(AGU Sponsor: T. Torgersen)

Previous comparisons between silicate mineral weathering rates in the field and dissolution rates in the laboratory have not been well constrained. but have generally indicated that laboratory rates are at least an order of magnitude faster than field rates. We have conducted wellconstrained experiments on irrigated plots and very small catchments and obtained similar results. Uncrushed, weathered minerals from our field sites placed in laboratory reactors dissolve at essentially the same rate as. crushed, fresh minerals. The reason for the discrepancy between field and laboratory is not "aging" of the minerals or formation of protective surface layers.

Two explanations can be offered for the slow apparent rates in the field: (1) solution composition in the field is not identical to that used in lab experiments (comparisons are usually based on a single parameter such as pH, and it is assumed that solutions are sufficiently far from saturation with primary phases that back reactions can be ignored). Dissolution in the field may be inhibited either by the accumulation of a solute (such as AI) that reduces dissolution rate, or by approach to saturation (the chemical affinity effect). (2) at high flow rates flow takes place through macropres, so much of the mineral surface area is effectively out of contact with "fresh" solution. Solution in micropores has a long residence time and so

9

dissolution rates decrease for chemical reasons. In reality, these explanations represent a continuum. At very slow flow rates, there should be little difference between the compositions of solutions in macropores and micropores, the time available for reaction will be long, and dissolution will be inhibited for chemical reasons. As flow rate increases, the rate- limiting process will progressively shift from a purely chemical process towards diffusional transport between micropores and macropores.

Similar processes will affect most other types of chemical reaction between minerals and solution in soils and aquifers.

Seismic Detection, Character'mtion, and Monitoring of Subsurface Fluids and Their Flow,

Amos Nur m e Stanford Rockphysics Laboratory; & The Stanford Crustal Fluids Center) Geophysics Department, Stanford University, Stanford, CA 94305-2215;Phone:415/723-0839;Fax: 4151723-1 188; email: [email protected]. Edu) (AGU Sponsor: Amos Nur)

No matter how many wells are drilled in a given crustal system (aquifer, oil field, fault zone) it is typically impossible, because of geological heterogeneities, to determine the detailed distribution of subsurface fluids, what they are, their pressure, and their mobility. Surface and to some extent borehole seismic measurements offer the greatest potential to obtain fluid related details. To accomplish this, it is necessary to understand the relations between seismic response of rocks with fluids to their mechanical and hydraulic properties and the acoustic properties of the pure fluids themselves. Results of laboratory and thearetical studies show that velocities are effected to various degrees by stress, pore pressure, fluid and rock compressibility, pore and crack geometry, proximity to rock failure temperature, fluid viscosity, fluid type, partial saturation, and weuabiiity.

The relation above suggest that accurate insitu seismic measurements should enable us to map spatial as well as temporal variations in pore pressure, amount of fluid, and pore space configuration. Successful examples are seismic changes observed during steam floods and water floods in oil fields. Intriguing possibilities are the monitoring of temporal changes of velocities in fault zones to infer pore pressure changes.

Yodeling Complex Systems: What can be done?

N. Oreskes and K. Belitz (Both at Department of Earth Sciences, Dartmouth College, Hanover NH 03755; 603- 646-1 420; e-mail: [email protected] [email protected])

The success of science has been generally credited to the power of scientific theories to make accurate predictions about nature. However, the predictions of geological and geophysical models are often made on geographical and geochronological scales that preclude direct testing. Therefore, scientists commonly attempt to test models by demonstrating correspondence between model output and short-duration or geographically restricted observational data. But, as we have argued elsewhere (Oreskes et al., 1994) a match between observationat data and model output does not ensure that the model is a reliable representation of nature. If correspondence between output and observational data is an insufficient test of a model. then how can we distinguish between a good model and a poor one?

Judgment of models must include evaluation and discussion of at least three additional criteria: the underlying conceptualization, the empirical adequacy of the governing equations in describing the physical processes at work, and the quality and quantity of the model input parameters. In this paper, we focus on the issue of input parameters, and argue that three categories should be identified: 1) empirically determined, 2) empirically constrained, and 3) empirically unconstrained. If our goal is to produce reliable representations of nature, then we must work to increase the

mailto:[email protected]

number of parameters that fall into the first category,’to narrow the range of the constraints in the second category, and to eliminate the third category altogether.

References Oreskes, N., et ai., 1994. Science 263: 641 -646.

Tuesday, June 7, 1994

Morning Scaling and Evolution of Fradure Nehvorks and Fluid Flow in Space

and Time

C. C. Barton (U. S. Geological Survey, Box 25046, MS 940, Federal Center, Denver, Co 80225)

Society’s need to recover fluid resources (water, oil, and gas) from the Earth, and to predict the movement of toxic waste requires quantitative models to describe and predict the movement of fluids in rock. Existing models based on porespaced flow are inappropriate for study of the more rapid process of fluid flow through fracture networks. This type of flow is not a simple function of the fracture characteristics at any particular scale, but rather the integration of contributions at all scales.

The mathematical constructs of fractal geometry are well suited to quantify and model relationships within complex systems that are statistically self- similar over a wide range of scales. Analyses show that natural fracture networks in rock follow a measurements of 17 twodimensional samples of three-dimensional lithology, and tectonic setting) show similar fractal dimensions in the range 1.3-1.7. The small range in fractal dimension implies that a single physical process of rock fracturing operates over a wide range of scales, from microscopic cracks to large, regional fault systems.

The knowledge that rock-fracture networks are fractal allows the use of data from a onedimensional drill-hole sample to predict the two- and three- dimensional scaling of the fracture system. The spacing of framres in drill holes is a fractal Cantor distribution, and the range of fractal dimension is 0.4-0.6, which is an integer dimension less than that of framre-trace patterns exposed on two-dimensional, planar sections.

Analysis of 17 twodimensional fracture network maps shows that the fractal dimension for a fracture network at the percolation threshold is close to 1.35, in contrast to 1.6 for bond permlation clusters. The pattem of p a l e groundwater flow has been mapped on a two-dimensional slice. through a fracture network and has a fractal dimension of 1.3. The pattem is geometrically analogous to the fractal backbone of flow (displacement of a viscous wetting fluid by a non-viscous, non-wetting fluid) through two- dimensional bond percolation clusters, which has a fractal dimension of 1.3.

Void Topology and the Hydromechanical and Geophysical

LR Mver (Earth Sciences Division, 50E. Lawrence Berkeley

NGW Cook (Department of Material Sciences and Mineral

A fracture can be viewed conceptually as a collection of interconnected voids lying more or less in a single plane. In this sense, a fracture could be considered a two dimensional porous media. An important distinction between the two, however, is that the shapes of the fracture voids are generally more crack-like, so that fracture propemes are more stress sensitive than porous media properties. Recognition of the importance of fracture void topology and stress sensitivity has led, in the past several years, to significant new understanding of the mechanical, hydrologic and geophysical characteristics of fractures. As mess is applied in a direction normal to the fracture plane, cracks begin to close with the longest closing first. This results in a nonlinear load-deformation curve with stiffness increasing with applied load. In an elastic medium, this nonlinearity is reversible. The

Laboratory, Berkeley, CA 94720)

Engineering, UC Berkeley, Berkeley, CA 94720)

10

hydrologic properties of fractures depend not only on the size of-the fracture voids but on their interconnectivity. As stress is applied normal to the fracture plane both the local void apertures and the interconnectivity of those voids changes. Consequently, single and two phase relative permeability and capillary pressure propemes of fractures are stress sensitive, and the validity of the cubic law, as normally interpreted, is questionable. Application of concepts from graph theory makes tractable the study of the relationships between void topology and fluid flow. Results imply that large portions of the void space do not contribute significantly to flow in a fracture. The concentration of voids in a fracture plane as compared to the adjacent material leads to a local increase in displacement in the plane in response to an applied stress. This increase in displacement results in a frequency dependent increase in the group time delay and a reduction in amplitude of a seismic wave propagating across the fracture. These effects will also be stress-dependent due to the nonlinear load-deformation curve of a fracture. Fluids or fracture infilliig will affect the wave propagation by changing the fracture stiffness and causing additional attenuation by viscous dissipation. At angles of incidence greater than the critical angle, energy wili be trapped as interface waves or guided waves even though the material propemes of the intact rock surrounding the fractures do not change.

Session I:

P-A~ON Linking q u a n t u m mechanics, molecular dynamics, and

thermodynamics: Es t imat ing the surface pro tona t ion of goethite

A. R Felmv, J. R Rustad, and D. M. Sherman (Pacific North- west Laboratory Richland, WA 99352)

Amorphous and crystalline ferric oxides and oxyhydroxides strongly bind many different metal ions, oxy-anions, and organic chelates. They occur ubiquitously in many natural systems either as discrete phases or as surface coatings and have high specific surface areas. Both the angstrom-scale ferric oxide surface structures and the reactivity of their proton binding sites have been difficult to evaluate experimentally. An approach is outlined which uses new capabilities in both quantum mechanical and molecular dynamics methods to study the surface and bulk properties of selected ferric oxide and oxyhydroxide compounds. These new capabilities include (1) a Hartree-Fock quantum chemistry code for periodic systems which can com U t e accurate energies for sys t em with unpaired electrons and a

approach include: 1) determination of the structures and rela-

with no solvent present; (2) determination of the most reactive sites for proton adsorption, as indicated by their relative proton affinities with no solvent present, (3) providing solvation correc- tions to the relative surfam energies and relative proton affinities; and (4) assessing the improvement in thermodynamic models of proton adsorption as a result of our enhanced understanding of surface structures, site types, and proton binding energies.

This approach has been tested by fitting an Fe3+-HzO potential function to the quantum mechanical calculations of Curtiss et al., J. Chem. Phys., 86, 2319, 1987. We use this potential to estimate the relative surface pKa of several sites on solvated [hexaaq~airon(III)]~+ and [di(ji-hydroxo)octaaquadiiron(IIi)]*+ using free-energy perturbation methods.

molecular dynamics model for dissociating water. Steps in t b is

tive stabilities of di if erent ferric oxide and oxyhydroxide surfaces

DETAILED HETEROGENEOUS PORE SCALE MODELS FOR TRANSPORT COUPLED TO CHEMICAL REACTIONS AND MULTI-PHASE FLOW

D R Janecky and S Chen &os Alamos National Laboratory, Los Alamos, NM. 87545; ph. 5056654253; fax 5056654955; Internet: [email protected])

Detailed mapping of subsurface properties to characterize the impacts of spatial and temporal heterogeneities on transport and chemical reactions

requires Commensurate modeling capabilities for integration, evaluation of scale dependencies and sensitivity analysis. Interrelated factors such as rock fabric, mineral distribution, porelframre geometry, and flow network topology at micro- to macroscales significantly increase the level of detail neceSSary to quantitatively evaluate processes of transport, extraction, deposition and alteration. Lattice-Boltzmann models provide an approach for examining flow and transport processes in such complex structures, resulting in efficient calculations on massively parallel computers. Models are currently being developed for single or multiphase transport and coupled multicomponent chemical interactions with steady state or dynamic pore networks. Geologic applications allow quantitative evaluation as a function of scale of processes of significant importance to environmental remediation, petroleum production, and natural transpodalteration.

Effects of Scale on Di spe r s iv i ty and H y d r a u l i c C o n d u c t i v i t y B e h a v i o r i n a C a r b o n a t e A q u i f e r

D i r k Schuize-Makuch. Depa r tmen t o f G e o s c i e n c e s , U n i v e r s i t y o f Wiscons in -Mi lwaukee , W I 53201

D o u g l a s S . C h e r k a u e r , Depa r tmen t o f Geosciences, U n i v e r s i t y o f Wiscons in-Milwaukee , W I 53201

T h e sca le d e p e n d e n c y o f h y d r a u l i c c o n d u c t i v i t y a n d d i s p e r s i v i t y i s w i d e l y r e c o g n i z e d . However, no f u r t h e r r e l a t i o n s h i p h a s b e e n e s t a b l i s h e d t o a l l o w a n e x t r a p o l a t i o n f rom i n e x p e n s i v e l a b e x p e r i m e n t s o n t o f i e l d sca le p r o b l e m s . T h e a u t h o r s a n a l y s e d two common h y d r o g e o l o g i c a l f a c i e s a n d e s t a b l i s h e d a f a c i e s d e p e n d e n t s c a l e b e h a \ - i o r f o r b o t h o f t h i s a q u i f e r p a r a m e t e r s .

T h e t w o a n a l y s e d f a c i e s were t a k e n f r o m t h e d o l o m i t e a q u i f e r o f s o u t h e a s t e r n W i s c o n s i n : a d e n s e , f r a c t u r e d muds tone f a c i e s a n d a p o r o u s p a c k s t o n e - b o u n d s t o n e f a c i e s . The mudstone f a c i e s i s a d o u b l e - p o r o s i t y f l o w medium. t h e p a c k s t o n e - b o u n d s t o n e f a c i e s a p o r o u s f l o w medium.

Pe rmeamete r t e s t s are c o n d u c t e d t o determine means a n d s t a n d a r d d e v i a t i o n s o f h o r i z o n t a l h y d r a u l i c c i ~ n d u c t i v i t y a n d l o n g i t u d i n a l d i s p e r s i v i t y f o r e a c h h y d r o f a c i e s o n t h e c e n t i m e t e r s c a l e . T h e a v a i l a b l e data base on t h e a q u i f e r t e s t scale was a n a l y s e d a n d revealed h y d r a u l i c c o n d u c t i v i t y increases re la t ive t o scale f o r b o t h t h e p a c k s t o n e - b o u n d s t o n e fac ies a n d t h e muds tone facies. T h e s e scale increases are f a c i e s s p e c i f i c . F i e l d scale hydraul ic c o n d u c t i v i t y and dispers ivi ty values are o b t a i n e d by monitoring t h e i n f l u x of L a k e M i c h i g a n w a t e r i n t o t h e dolomite a q u i f e r . T h e a d v e c t i v e f r o n t can b e f i x e d i n space a n d t i m e d u e t o t h e d i f f e r e n t composition o f L a k e M i c h i g a n water a n d a m b i e n t ground w a t e r . O t h e r f i e l d sca le v a l u e s were o b t a i n e d f rom v a r i o u s c o m p u t e r models.

Geochemical Kinetics and Transport Coupling in Hydrogeologic Systems

WA 99352; 509-375-4392; e-mail: cisteefelOpn1.gov) Carl I. Steefel (Pacific Northwest Laboratory, MS K3-61, Richland,

Although the local equilibrium assumption (LEA) has been a fundamental tenet of many geochemical, petrologic, and hydrologic studies for years, a growing body of evidence suggests that in many cases it does not apply. Increased experimental data on mineral-water reaction rates have greatly improved our understanding of the range of validity of the LEA, but additional information is necessary in order to accurately characterize reaction and transport coupling in hydrogeologic systems. In particular, a knowledge of the reactive surface area and its relation to the transport properties of the rock is required. At the simplest level, the system behavior is determined by the characteristic time and length scales of the processes involved and not by the size of the system as a whole. For example, the appropriate length

scale for flow across a thermal boundary layer may be on the order of meters even though the boundary layer occurs in a kilometerscale hydrothermal system. It is not possible to define a single length scale, however, if a system is physically and/or chemically heterogeneous. The effect of physical heterogeneity alone is demonstrated by an example in which the solute concentration and reaction rate profiles in fractured rock difier substantially from those predicted in rock with a homogeneous hydraulic conductivity distribution. Combined chemical and physical heterogeneities can have an even more profound effect on reactive transport because of the coupled nature of the processes. For example, the large-scale system behavior may be significantly different depending on whether there is a positive or negative correlation between the spatial distributions of reactive surface area and hydraulic conductivity. Because of this and other effects relating to the presence of heterogeneities, validation of reactive transport models must ulti- mately be carried out in the field. Several possible ways of doing so are discussed. Laboratory and computer experiments, however, may prove useful in developing a fundamental understanding of reactive transport in heterogeneous media. Their usefulness is demonstrated with several examples.

Estimation of Scaling Errors via Lattice Gas Automata: Application to Diffusion and Adsorption.

H.W. Stockman (Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 871 85-0750; 505-844-0975; [email protected])

Transport coefficients for solutes in geologic media are often estimated from tests with very short flow paths. Such tests can overemphasize transient behavior, yielding errors in the measured adsorption and diffusion coefficients. These errors can be estimated with lattice gas automata (LGA). A model LGA system is constructed with known diffusion coefficient (D) and adsorption and desorption rates (k. and k.,). A flow "experiment" is performed on the system, and the apparenf D, k, and the breakthrough curve, producing an estimate of error. The LGA tests confirm the experiments of W. Gill and coworkers, who showed that small buoyancy differences, resulting from variations in solute concentration, can yield factor of 2 to 10 errors in D measured by the Taylor-Aris method. Errors in the apparent distribution coefficient K, = k. / k., have two principal causes: deformation of the solute bolus at very high Peclet number, and the slowness of adsorption for many solutes and substrates. In geologic media, the first cause usually becomes unimportant within a few characteristic diffusion times (= R*/D, where R is the fracture or pore width), but the second can yield a significant disagreement between K, measured in flowing vs. batch experiments.

are inferred from the shape of

Temporal and Spatial Variations of Ekacture Propagation: Fluid Pressures in Contact Metamorphic Environments

B Dutrow (Dept. of Geology & Geophysics, LSU, Baton Rouge, LA 70803; ph. 504-388-2525; dutrowOhermes.geo1.lsu.edu)

Spatial and temporal aspects of fluid flow, and the resultant thermal and chemical consequences, are closely coupled with the opening of a percolation pathway. Fractures generally provide the dom- inant pathway by which infiltrating fluids access the rocks. At mid-crustal levels near thermal perturbations, fractures are dy-

11

namic features that propagate in response to fluid pressure ( P j ) . Pf increases in isolated fluid-filled pores in response to thermal energy dissipation through the host rocks. Fracturing occurs when Pf attains a critical value, dependent on rock strength and pore geometry. Flow within the lengthened fracture dissipates overpressures and returns Pj to local equilibrium conditions. Because Pf dissipation is orders of magnitude faster than Pf buildup, episodic behavior ensues. Pj cycling continues throughout the prograde thermal event until the rate of thermal input declines.

Heat transport from a 2km steep.walled intrusion, coupled with thermomechanieal properties of H2 0-rich fluids and equations for Mode I fracture deformation and propagation formulated in terms of Pj, has been modeled to evaluate Pj as a function of time. For K:s of 1.4 - 3 . O M P a f i and initial fracture lengths of .001- .lm, model results indicate that thermally induced Pf are of suEcient magnitude to drive rock fracturing. At loom, fracture propagation occurs continuously throughout the first 1000 yrs, increasing the likelihood of establishing permeable flow networks. At 50Om, fractures propagate more slowly but episodes continue for greater time periods. These results suggest that flow, and hence fluid mineral interactions, proceed at disparate times in the inner and outer aureole. Fluid flow accompanying metamorphism is spatially and temporally restricted and may not be a continuous process.

MODELING OF FLUID FLOW AND MINERAL REACTIONS AT SEAFLOOR HYDROTHERMALVENTS USINGHYDRODYNAMICAL CELLULAR AUTOMATA

W.C. Shanks. III (US. Geological Survey, Denver, CO 80225; ph. 303-236-2497; Internet: [email protected]) D.R. Janecky, and S.-Y. Chen (Los Alamos National Laboratory, Los Alamos, NM. 87.545')

Multicomponent solute transport and mineral precipitationldissolution has been coupled with Lattice Boltpnann Equation (LBE) models (a type of lattice gas automata). These models accurately simulate fluid flow on a twdiensional grid, including advective and diffusive transport, at Reynolds numbers up to 10o0. Execution on massively parallel oomputers allows explicit accounting for physical and chemical processes occurring at each node. The models are dimensionless, but seem most effective for micron- to meter-size scales. The power of the method is in the simultaneous computation of mineral precipitation/dissolution and the resultant change of porosity and permeability.

Chemical reactions at solid surfaces, including precipation and dissolution of solid phases, can be examined with the model because fluid flow and mixing, hydrodynamic transport, solute diffusion and mineral precipitation- dissolution processes are all treated explicitly with space and time. Chemical transport and development of hydrothermal chimney-like structures is modeled to understand the development of hydrothermal deposits at seafloor vent sites. Chimney shape and development is sensitive to vent velocity and mineral precipitation rate. Rapid precipitation produces MITOW self-sealing chimneys with thin walls, whereas slow precipitation relative to flow produrn bowl-shaped chimneys with dendritic walls. AdditionaJ simulations involving flow of hydrothermal fluid through porous chimney walls show that large changes in permeability occur as reactions proceed.

Fluids in Microporous Systems

J H Cushman (1150 Lilly Hall, Purdue University, W. Lafayette, IN 47907-1150; 317-494-8040; email: [email protected])

47907-1150; 317-494-9628; e-mail: [email protected])

J Curry (1 150 Lilly Hall, Purdue University, W. Iafayette, IN

Fluids as simple as a rare gas display an extremely rich, anomalous behavior when confined to a structured planar system

of width a few molecular diameters. The fluids phase diagram is changed, its' thermal transport coefficients are radically altered from that of the bulk, and it becomes inhomogeneous and anisotropic. The properties of the vicinal fluid depend in a complex way on the initial structure of the fluid, the structure and commensurability of the confining surfaces (walls), the wall-fluid potential, the separation of the walls, and asperities within the walls.

In this presentation we focus on the latter of these issues, but also provide limited information on the former. Virtual experiments in the isostrain and isostrain-isostras grand-canonical, micro- canonical and canonical ensembles are described.

STUDY OF PARTICLE TRANSPORT IN SATURATED AND UNSATURATED FRACTURED POROUS MEDIA AT SCALFS DOWN TO MICROMETERS

Jiamin Wan, Chin-Fu Tsang, and Tetsu K. Tokunaga (Lawrence Berkeley Laboratory. Earth Sciences Division, MS SOE, 1 Cyclotron Rd., Berkeley, CA 94720; tel. 510486-6004)

Previous studies suggest that solute migration can be significantly enhanced via sorption onto and transport with mobile colloids. In unsaturated media two types of interfaces are present, the mineral-water interface and the gas-water interface. There is a general belief that colloid sorption occurs at mineral surfaces only, neglecting the possible importance of gas-water interfaces. Many other processes controlling transport in fractured porous medium currently remain poorly understood. Various concepts concerning the nature of fracture-mahix interactions in advective and diffusive- dispersive solute and colloid transport have been developed. However, these concepts have generally not been experimentally tested at the necessary high spatial resolution. This paper describes a new method to test colloid transport models, providing an alternative way towards understanding particle transport mechanisms in saturated and unsaturated-fracture porous medium.

Dual-porosity glass micromodels have been very recently developed, for the first time, to directly visualiziig the behavior of individual paxticles within hcture. porous media. The fractures have dimensions in the range of 100 to 400 pn, and the matrix has pore sizes ranging from 4 to 50 pm. Three types of Polystyrene latex particles (-1.0 pm) with different charge and surface hydrophobicity are used as model colloids. At controlled flow rates, matric potentials, and solution chemistxy, the following phenomena are beiig studied: (1) relative flow rates in fractures and the porous mamx, (2) comparisons of particle sorption and desorption on fracture surfaces and mamx surfaces, (3) the extent of particle sorption and desorption at the gas-water interface vs. at solid surfaces, and (4) the matric potential influences on particle retention in unsaturated fractured porous media.

Tuesday, June 7,1994 Aftern oonLEvening

Session II: IWEXRING PROCESS

Water Circulation in Metamorphism

D. Rumble. m (Geophysical Laboratory, 5251 Broad Branch Rd, N. W.. Washington, D.C 20015; 202-6862483; e-maik [email protected])

There is "too much" water in a variety of crustal environments, including sedimentary basins and regional metamorphic belts. Regional and contact metamorphic rocks have time-integrated fluxes

12

of 106 cm3 water/cm2 for pervasive flow and up to 109 cm3 water/cm2 in fracture flow, amounts far greater than can be supplied by dehydration of immediately subjacent rocks. The types of evidence supporting high water fluxes are so numerous and varied, including petrologic. mineralogic, textural, microsrmctural. and stable isotopic data, that it is unlikcly that a l l of them coold have been interpreted erroneously. Thus, the question arises as to what mechanisms of permeability enhancement might operate to facilitate large fluid fluxes. Field evidence suggests the operation of reaction enhancement of permeability, grain scale dilatancy, and hydraulic fracturing during metamorphism. All of thesc mechanisms are inherently episodic and transient The transport properties of dynamic permeability enhancement are poorly known in nlation to the thermal and &formational cycles of metamorphism. Future research should be directed towards experimental and theoretical simulation of permeability enhantxment with close collaboration between isotope geochemists, structural geologists, and perrologists to field =st models of permeability enhancement

Geochemical Evidence for the Origin, Evolution, and Flowpaths of Saline Groundwaters in a Regional Flow System: Midcoatinent, USA

M Musgrove and J L Banner (Both at: Department 0fGedogicaf Sciences, University of Texas, Austin,TX 78713'1909; tel. 512- 47 1-50 16; e-mail: [email protected]) Lower Paleozoic strata in southeastern Kansas, southwestern Missouri and northern Oklahoma are predominantly marine carbonates that comprise portions of three r eg iod flow systems. Groundwaters in these three adjacent systems exhibit extreme chemical and stable and radiogenic isotopic variationsthat delineate large-scale fluid mixing processes and provide evidence of two mechanisms for the generation of saline fluids. Hydrodynamic and geochemical data closely correlate with ge0,gaphic location and indicate that each system contains waters of markedly different origins. Results of elemental and isotopic mass balance modeling demonstrate that fluid mixing processes exert a fundamental control on groundwater compositions over the 40,O kmz study area. This quantification of groundwater mixing provlries an important basis for determining endmember water compositions; one dilute and two saline, and evaluating hydrologic models for these flow systems.

One of the saline endmembers is a Na-CaCI fluid that migrates east- ward in the northern part of the Western Interior Rains aqaifer system. Integration of the elemental and isotopic composition of this groundwater with hydrologic data reflects a hvwmmponent origin resulting from a mixture of 1) far-traveled, relatively dilute meteoric groundwaters recharged in high altitude areas a k m west of the study area, and 2) saline Na-Ca-CI fluids resulting from the subsurface dissolution of Permian halite and subsequent water-rock interaction during downward migration through uoderlying Pennsylvanian shales. These results allow development of a model for the formation of saline Na-Ca-Cl fluids, a cornmoll oomponent of many sedimentary basins, and the l a r g e - d e -caUy driven flow of this system p v i d e s a modem analog for models of similar regional-scale systems. Analysis of the processes controlling the chemical and isotopic composition of this groundwater p v i d e s insight into hydrologic models for this region, specifically yielding geochemical evidence for physical flow processes such as large-scale groundwater migration and cross-formational flow.

Coupling Hydrothermal Fluid Flow to Thermal Maturiiy for a Triassic Basin Using Fluid Zndusions and Fission Track Length Distributions

TC &stoa, Hsii-Yi Tseng. G Gao @ept of Geological and Geophysical Sciences, Princeton University, Princeton, NJ 08544) RC Burmss (U.S.Geo1ogical Survey, Denver, CO 80225) DS Miller @ept of Geology, Rensselaer Polytechnic Institute, Troy, NY 12180)

The Late Triassic Taylorsville basin yields dehitai fission track apatite and zircon dates that are younger than the age of deposition. The apatite fission track ages range from 135 to 200 Ma with the younger ages located near the center of the basin. The spatial position of the fission track samples suggest that either the Taylorsville basin was more deeply buried than today

and was exhumed prior to the Early Cretaceous or an extremely high geothermal gradient existed for a prolonged period of h. Maximum homogenization temperatures of secondary aqueous fluid inclusions in calcite veins in shale and sandstone cutthgs from a borehole near the center of the basin range from 150" to 200°C between 6650 and 10070 f t depth, with the highest temperatures in the deepest samples. Calcite vein containing CHq-rich inclusions record entrapment pressures of 400 to 500 bars with the higher pressures in the deeper samples. The pressures are consistent with the present lithostatic gradient. If they were trapped under a hydrostatic gradient, then subsequent compaction combined with removal of 1-2 kms. must have occurred. If the aqueous and CHq-rich inclusions are concordant in age then together they record a paleogeothemal gradient. If the pressure gradient is close to lithostatic, then the thermal gradient would have been about 85"Ukm. If it represents a hydrostatic gradient, then the thermat gradient would have been <4oocflun. To match the integrated dates, the thermal maximum would have occurred at -200 Ma, consistent with rapid burial of the Taylorsville basin to twice its present day depth and thermal reequilibration with a 40"Ukm geothermal gradient- To reproduce the fission track lengths the thermal maximum must have been followed by slow exhumation. Higher geothermal gradients would require advective heating by fluid migration.

Space-Time Variation of Hydrologic Parameters Considering Scale and Information Content

S P Neuman (Department of Hydrology and Water Resources. The University of Arizona. Tucson. AZ 85721; 602621-7114)

Flow and transport parameters (permeability. seepage velocity, dispersivity) have been traditionally viewed as well-defined local quantities that possess unique values at each point in space (and possibly time). Yet in practice they are usually determined at selected well locations and depth intervals where their values depend on the scale and mode of measurement. Such data are typically cor- rupted by experimental and interpretive errors; using them to estimate parameters at other locations. and on other scales, introduces additional uncertainties. Thii renders the parameters random and the corresponding flow and transport equations stochastic. The stochastic flow and transport equations can be solved numerically by (conditional) Monte Carlo simulation, but this tends to be computationally demanding and to yield results of unknown reliabiity. Deter- ministic moment equations which offer an alternative to Monte Carlo simulation have recently been developed for steady state saturated flow [Newnan and Orr. 19931. transient unsaturated flow [Neumun and Loeven. 19941. and solute transport [Newnun, 19931. These equations provide optimum predictions of flow and transport in light of the available data and assoCated uncertainty. They generally differ from traditional deterministic flow and transport equations (which are therefore not optimal) both in form and in the nature of their parameters. The optimal equations generally involve integrals and spatially varying local and nonlocal parameters (the latter depending on more than one point in space and/or time). The traditional concept of an REV (representative elementary volume) is neither necessary nor relevant for their validity or application; among others. these equations apply to fractal media above some cutoff. The parameters are non- unique in that they depend not only on local medium properties but also on the information one has about these properties (scale. location. quantity. and quality of data). Darcy's law and Ficlc's analogv are generally not obeyed by the flow and transport predictors except in special cases or as approximations. Such approximations may yield familiar-looking differential equations in which however the parameters are non-unique. depending on scale and information content. We briefly explore these equations theoretically and numerically.

The involvement of Modern Theoretical Methods to Study Atomic Scale Phenomena of Geochemical Importance

A. C. H a (Solid State Theory Group, Molecular Sciences Research Center, Pacific Northwest Laboratory, Mail Stop K1-95. P.O. Box 999, Richland, WA 99352; (509) 375-2052)

Although geological processes are often viewed on the macroscopic scale, the underlying chemistry is controlled by molecular scale phenomena. The

13

study of atomic scale processes has traditionally been the realm of the chemical physics community which has employed computational quantum mechanics and molecular dynamics in conjunction with spectroscopic and diffraction experiments to study microscopic phenomena. Recent advances in quantum mechanical methods are allowing researchers to accurately describe chemical speciation, adsorption and chemical reactions which occur in geophysically important systems. Studies using such theoretical methods are demonstrating that chemical controls on hydrogeologic processes (including reactivity, adsorption, and dissolution) are highly dependent upon the specific surface which is being considered as well as the external morphology and surface area of the sample.

A description of the current stateof-the-art in atomic scale theoretical methods (either quantum mechanically or classically based) capable of treating phenomena on ultra short time and length scales will be presented. Several applications of these methods to geochemical systems will also be discussed in detail.

Tuesday, June 7,1994 Evening

Session III:

P-ATION LABORATORY TESTS OF

Measurement a n d Simulation of Fluid Flow in Real Fractures: A Reality Check

Livennoxe, CA 94550; 5 10-422-7046) W B Durham and B P Bonner (Eaah Sciences Dept, UCLLNL,

S R Brown (Geomechanics Dive, SNL, Albuquerque, NM 87185;

N&cal simulation of fmcture flow is an important tool for gaining insight into the hydraulic behavior of individual fractures. For instance, the process of "channeling" was never widely appreciated until simulations gave us visual images of parallel plate flow degenerating into channels as mean fracture apertwes decreased. We have applied one simulation, that based on Reynolds' approximation to the Navier-Stokes equations [Brown, JGR, 92,1337,19871 to joints whose hydrologic and mechanical behavior and topography were established by laboratory measurement. The motivation for the laboratory work has been to build a base of results against which numerical and analytic models can be tested, and the present work represents the first attempt at model verification.

505-844-774)

The laboratory measuremnts were canid out on (Brazil) tensile fractures in samples of low matrix permeability granites, Westerly (RI) and Harcoun (S. Austdia). The area of the axial fractures was roughly 140 x 140 mm. The shape of each fracture was carefully digitized before and after the hydmlogic tests. An important feature of our digitizing pmfilometer is near microscopic positional alllacy in the fracture plane, providing an accurate image of the joint space at a spatial resolution of approximately 50 pn. For the hydrologic testing, samples were reassembled (following profiling) in carefully registered or in slightly offset configurations, the latter to simulated a more open joint. Joint normal deformation and joint permeability were measured to joint n o d stresses to 160 Mpa (applied hydrostatically to the outer cylindrical surface). We saw in all cases that joint permeability initially decreased as the third power of the mechanical aperture (i.e. following the parallel plate approximaton), but that it then became more sensitive to aperture at small values of the aperture, presumably because of increasing tortousity of flow. Simulations using Reynolds' approximation agreed qualitatively with the breakdown of the parallel plate approximation, but did not show as strong a sensitivity of permeability to aperture as was actually observed. We are performing additional tests and simulations to determine if Reynolds' approximation is inappropriate (which we doubt) or if subtle e m r s in digitization tend to overestimate local aperture.

14

Reduction and Diffusion of Selenium in Soil Aggregates: Synchrotron X-ray Fluorescence Microprobe Studies of Intra- aggregate Chemical Heterogeneity Formation.

T. K. Tokunagq (Lawrence Berkeley Laboratory, Earth Sci. Div.

S. R. Sutton, and S. Bajt (Dept. of the Geophys. Sci. and Center MS 50E, 1 Cyclotron Rd., Berkeley, CA 94720; tel. 510-486-7176)

for Advanced Radiation Sources, The Univ. of Chicago, Chicago, LL 60637; teI. 516-282-2187)

The mechanism of diffusion-limitted transport over relatively short distances ( 4 0 mm) has often been invoked to help explain features of more macroscopic observations (column-scale solute breakthrough curves). However, experiments conducted in support of these various micro-scale models have seldom been subjected to direct measurements at scales appropriate for model testing. Direct, high resolution, measurements on trace element distributions within soils are possible through the use of the synchrotron x-ray fluorescence microprobe (SXRFM), permitting testing of models which invoke small-scale heterogeneities with respect to solute transport.

The SXRFM at the National Synchrotron Light Source (beamline X26A) was used to map distributions of selenium and other elements within soils contaminated with Se. Our previous studies revealed large variations in total Se concentrations over short distances (2 1 mm) within soil aggregates collected from the Se- contaminated Kesterson Reservoir. In later studies, water-soluble Se(V1) was introduced into formerly uncontaminated soils. Influences of soil aggregate size, water-saturation, organic matter inclusions, and time were studied with respect to generating heterogeneous distributions of Se. Samples with embedded, decomposing root sections developed the greatest heterogeneities with respect to Se concentrations. Such heterogeneities may have resulted from S e reduction to less mobile Se(IV) and insoluble Se(0) in the region of active organic matter decomposition, which in turn induced Se(VI) diffusion towards such zones for further reductive concentration. This model was compared favorably with an analytical solution for transient Se(V1) diffusion to reducing zones. Further measurements which combined the S X R F M with the valence- sensitive method of x-ray absorption spectroscopy supported the proposed model through providing direct evidence for the presence of Se(0) and Se(IV) in the accumulation zone.

Rate of Permeability R e d u c t i o n in G r a n i t e at Elevated T e m p e r a t u r e s

D A Lockner, D E Moore, and J D Byerlee (U S Geological Survey, Menlo Park, CA 94025; 415-329-4826)

In recent years a variety of models have been proposed in which high fluid pressures contribute to the generation of earthquakes at low stress on large crustal faults. Different mechanisms have been proposed to maintain abovehydrostatic fluid pressure within the fault zone. Rice (1992) has considered a continuous source of (mantle-derived) fluid migrating up through deep rooted fault mnes to maintain near-lithostatic fluid pressure within the fault. Bya lee (1990) showed how a stable pressure distribution could be established in which the core of the fault zone maintained near-lithostatic fluid pressure without a need for fluid flow. This condition can occur if a threshold pressure gradient exists below which fluid does not flow within the fault zone. Alternatively, Byerlee (1993) has proposed a model in which the fault zone establishes fluid compartments that become hydraulically isolated from each other and from the surrounding country rock. These compartments, which probably have linear dimensions on the order of 100 m or less, are established when impermeable seals are formed by precipitation and alteration reactions driven by the high reactivity of the fine-grained fault gouge material. These seals are likely to be destroyed with the occurrence of each large earthquake. Thus, if this fluid compartment model is correct, the seals must be able to re-form in the interseismic period in a matter of 10 to 100 years. To determine whether these sealing rates are realistic, we have measured permeability changes in water-saturated granite samples at temperatures from 300 to 500°C. Nominal fluid

pressure of 100 MPa and confining pressure of 150 MPa were maintained in all experiments which typically lasted 3 to 5 weeks. Three sample geometries were tested: solid right-cylinders of intact rock, a 'sandwich' configuration in which a thin layer of powdered granite was placed between discs of intact granite, and a fracture geometry in which a sample was split axially in tension and then reassembled to measure flow along the fracture. In all experiments, permeability decreased with time, typically obeying an empirical form: loglo k = a - t / ~ , where k is permeability, t is time and a and T are constants. For intact samples, T ranged from 10 to 140 days and decreased systematically with increasing temperature. When extrapolated to 200°C, the intact data suggest a time constant of 175 days or, stated another way, permeability would drop 4 orders of magnitude in under 2 years. 'Sandwich' experiments lost permeability even more rapidly than intact samples. In addition, the fracture sample run at 400° and the two intact samples at 500" all underwent abrupt sealing episodes in which permeability dropped by over 2 orders of magnitude after a delay of 5 to 12 days. Thus, these experiments support t h e hypothesis that faults and fracture systems at mid-crustal depths can lose permeability and establish pressure seals rapidly. Given t h e proper conditions, near-lithostatic fluid pressure is likely to develop.

Percolation Modeling of Permeability Evolution during Hydrothermal Compaction

WeQ arc, Christian David C) and Teng-fong Wong (State University of New York, Department of E& and Space Sciences, Stony Brook, NY11794-2100) C EOPGS Labomtoire Materiavx, f-67084 Strasbourg, France)

Fluid t r a q r t in seismogenc and sedimentaiy settings are dosely related to the temporal and spatial distribution of porosity and permeabilii. Significant pomsily reduction may occur under hydrothema1 condidions by healing, sealing or cementalion plocesses. Recent hbocatory studies show that the penneabiii and formation fadoc are strongly porosity dependent d u m such hydrothermal ampadion process. Three regimes with disthdly daferent penneabilityoomsity relatiinshp have been obsenred in hotpressed Cawe (Bemabe et a/., 7982; Zhaq et d., 1994) and quartz ( k d m r , 1990), and Fontainebieau sandstones with different degrees of cementation (f?ouhk and .?immr, fm. W relatively high pomities the perrneabirny (k) has a power-law dependence on pow (41): k+* with n 4 (regime I), and there exists a cmssover pomsity be& which the power law no bnger appr i and an accelerated reduction in permeability was found (regime lo. Finally the permeabili becomes too small to be deteded although there are porosities remained, implying the complete loss of connedivity m the pore space (regime 111). In this ste, we developed a unified model to numerically simulate the evdution of permeabilii in regimes I and Il. We used pemlatii theocy and formulated a 30 nehvork model to analyze the effeds d pore shrinkage and connedivity loss on permeability in the different regimes. In regime I, porosity was reduced solely by pore size shrikage with connedibity fKed at 100% bond occupancy. Conductance elements were chosen randomly and the pore dimensions were reduced by shrinkage factors randomly distributed between 0 ad 1. In regime II, we assume that the hdhkb~al pores can be totally eliminated by the m p a C t i processes, and therefore permeability is reduced mainly by connedivity bss whereas the pore size distribution remains fad Incorporating quantitative m'crostrud&al data of pore size distribution in our network model, we obtained sirnulatin results on the evolufwxl of permeability and formation fador in both regimes which are in good agreement with laboratory measurements

Wednesday, June 8, 1994 Morning

Ab-Initio Models, Water-Rock Kinetics and Coupled Hy- drogeochemical Processes: Global Implications of A tomic Pl ienoniena

Antonio C. Lasaga, Josep Soler, Jiwchar Ganor , T i m Burch a n d Ka thy Nagy (Depar tmen t of Geology & Geophysics, Yale University, P.O. Box 6666, New Haven, CT 06511)

Recent kinet ic work on water-rock interactions links t h e atoni ic a n d global spatial scales. T h e - development of a fully in tegra ted r a t e law will b e discussed wi th special a t t e n t i o n to t h e impor tan t effects of deviat ion from equi l ibr ium on tlie ra tes of mineral-water reactions. T h e combined effects of tempera ture , pH, ionic s t r e n g t h a n d s a t u r a t i o n condi t ions on tlie overall dissolution a n d pre- c ipi ta t ion rates of minerals mus t be properly descr ibed before a n y seriously quant i ta t ive model of coupled fluid flow a n d chemical reaction can be undertaken. Based o n expe r imen t s a n d a tomic scale processes, a rate law t h a t integrates t h e s e effects, iiiciudiiig t h e functional ciepen- dence of t l ie rate o n AG,, t h e free energy change for t h e mineral react ion, is proposed. A n impor tan t resul t is t h e presence of a "surface transition" in t h e reaction mech- an i sm leading to a very s t rong non-linear dependence of t h e dissolution ra tes on AG,. T h e possible role of disloca- t ion defects in tliis "surface t ransi t ion" will be presented. T h e relat ion of global weathering rates a n d geochemical cycles to the recent experimental a n d theoret ical water- rock kinet ic work will t h e n be explored. T h e t e m p e r a t u r e effect on t h e silica content of s t r e a m s is reevaluated. T h e var ia t ion of silica concentrat ion wi th runoff in tlie world's rivers is quantified using a coupled fluid flow and reaction iiiodel and t l ie full r a t e law developed for a proto-granite systerii by t h e kinet ic experiments . Implications of t h e water-rock kinet ic d a t a for the cur ren t geocliemical cycles models will be analyzed with especial emphasis on t h e link between physical weather ing a n d chemical weathering.

scaling and Transport is Systems with Continuously Evolving Heteaogeneity

2 B Cushmaq (1 150 LiUy Hall, Purdue University, W. M a y e , IN 47907-1150; 317-494-8040; email: [email protected])

T R G ~ M (Ga- Department, m e PNL? POB 999,

Transport in porous media with fractal character hvolves fluctuations on all space and time scales. Conseqwnty one anticipates constitutive theories should be n o d d in character and involve constitutive parameters with arbitrary wave vector and frequency dependence. We provide here a nonequilibrium statistical mechanical theory of transport which involves both diffusive and convective miXing (dispersion) at all d e s . The theory is based on a generabition of classical approaches used in molecular hydrodynamics and on t imeamla t ion functions defined in terms of nonequilibrium expectations. The resulting constitutive laws are nonlocal and constitutive parameters are wave vector and frequency dependent. All results reduce to their convolution-Fickan, quasi-Fickian and Fickian counterjmts in the appropriate limits. Several examples are presented. Of particular note is an argument showing that convolution Fickian and quasi-Fickian transport occurs only if the average mean velocity is constant.

Richland, WA 99352; 509-376-7417)

15

Session IV: FLELD AND LARGE SCALE 'DETERMINATION' OF PARAMETERS Can Electrical Geophysical Measurements Tell Us Anything About Fluids in

Randall L. Mackia (Earth Resources Laboratory, Mass. Inst. of Technology, Cambridge, MA, 02139; email: [email protected])

Electrical geophysical measunnents are the geophysical measure most closely related to fluid volumes and fluid pressures. Thii is because in the upper crust, electrical conduction is due to the movement of ions through an interconnected fluid phase. High electrical conductivity implies high volumes of fluids. Indeed, the emperical connection between electrical conductivity, pore fluid conductivity, and porosity for sedimentary rocks is well laown as Archies Law. Modifications of Archies Law try to take into account other parameters such as fluid saturation and the presence of clay particles. It would seem, therefore, that once the electrical conductivity of the subsurface is determined, then the fluid properties could be easily computed. However, there are many complications from non-uniquenesses in the electrical interpretations to unknowns in the subsurface fluid chemistry, pore structure, and permeability.

In this talk, I will briefly review the common electrical geophysical methods and the relation of electrical conductivity to fluid properties. In addition, I will address more recent geophysical techniqes, such as ground-penetrating radar and electro-seismic coupling, that provide additional information about the subsurface physical properties. In particular, electro-seismic coupling is very promising because it has the potential to discern variations in subsurface permeability, fluid chemistry, and lithology.

the Subsurface?

Effective Hydraulic and Transport Parameters from Laboratory- and FieJd-Scale MeasuFements: A Method Inter-ComparisOn Study

G Teutsch (Geological Institute, Tiibingen University, Sigwartstr. 10, 72076 Tuebigen, FRG; tel. +49 7071 296468; e-mail:teutsch@mailserv. zdv.uni-tuebingen.de)

At the environmental research field site 'Horkheimer Insel' a detailed subsurface investigation program has been performed during the past 7 years. The site is located in the Neckar valley (Southern Germany) where the aquifer is formed by Quaternary sand and gravel deposits about 3-5 m thick. The aim of the study is to compare direct and indirect subsurface investigation techniques at various scales and to identify the characteristic properties of the individual measurement methods in a heterogeneous porous aquifer.

At first a detailed investigation of the subsurface was performed applying various direct and indirect hydraulic measurement methods at laboratory and field scale. The resulting hydraulic conductivity parametem range between 2.7*107and 8.1*10-' mls with a mean between l*lO-'and 3*104 m l s and a variance depending on the measurement method and the scale of investigation. Similarly, correlation lengths determined from variograms show a measurement method as well as a scale dependance. In a second step, various forced and natural gradient tracer tests were conducted over distances between 15 and 200 m. The results clearly reflect the heterogeneous strumre of the site with a longitudinal dispersivity not reaching an assymptodic value.

Using a non-parametric stochastic (Monte-Carlo) flow and transpoa modelling approach, it could be shown that the observed hydraulic conductivities at laboratory and field scale as well as the tracer test results were consistent - but they produced a large prediction uncertainty. Therefore, in order to reduce this iumrtainty. a borehole-borehole seismic tomography study was performed to help identify the geometry of the

sedimentary structures at the site. This information is introduced into the stochastic model as 'soft information.'

The paper presents the results obtained so far and will also describe some new approaches which are presently tested at the site.

M i c r o e a r t h q u a k e C lus t e r ing a n d t h e S l ip P r o c e s s on t h e San A n d r e a s Fault at Parkfield, California

R. Nadeau. T. V. McEvilly and W. Foxall (Center for Computational Seismology, Lawrence Berkeley Lab., and Dept. of Geology and Geophysics, University of California. Berkeley, CA 94720)

Doublets and multiple-member sets of earthquakes having very similar recorded waveforms have been observed at various scales. Such similarity derives from near-identical sources (mechanisms and dimensions) and wave propagation (path geometry and medium properties). Recent analysis of the 1987- !992 population of some 1700 earthquakes (M -0.5 to M 4.7) recorded by the high-resolution (125 Hz bandwidth) borehole- installed network of seismographs at Parkfield, California provides a new look at the phenomenon of microearthquake clustering within a 25-km section of the San Andreas fault. This section is of high interest for two reasons: 1) it is the nucleation region for the expected next M6 'Parkfield earthquake'. and 2) it is the transition zone between the locked fault segment (1 957 M8 break) to the SE and the creeping stretch to the NW. A rigorous measure of similarity characterizes the clustering phenomenon within the data space in terms of maximum size of the cluster 'patch' and recurrence properties of cluster members. Two interesting characteristics are seen in the results of the analysis. First, there appears to be a characteristic patch size of less than 200-300 meters (actual size is unknown because of the -200 m uncertainty in the hypocenters - this value will be reduced in the future to about 10 meters through application of the computationally- intensive high-precision relative location methods). Second, there appears to be a bimodal pattern in the recurrence times between highly similar cluster members for the 6-years data set. A sharp peak at the very short times (minutes or less) contains about 25% of the clustered events, while a second, broader peak. containing another 25% of the events. is seen at about 0.75 year recurrence time. Implications of this behavior for fault-zone process impact several topics of current interest, such as the nucleation dynamics for large earthquakes, the differences in properties, if any, between creeping and locked fault segments, and the influence of lithological and hydrological heterogeneity of fault zones on temporal and spatial variations in fault strength and slip.

Stoneley Wave Propagation Across Borehole Permeability Het- erogeneities

X.M. Zhao, M.N. Tok6z, and C.H.Cheng (Earth Resources Labora- tory, Department of Earth, Atmospheric, and Planetary Sciences, M.I.T., Cambridge, MA 02139)

The propagation of borehole Stoneley waves is strongly correlated with permeability of the formation. Using the theory of dynamic permeability and a finite dfierence technique in cylindrical coordinates, dynamic pore fluid flow in an arbitrarily heterogeneous porous medium surrounding the borehole is modeled. The effects of the flow 'on the borehole Stoneley waves are calculated. The numerical simulation results show that the continuous permeability variations in the formation have only minimal effects on the Stoneley wave propagation. Whereas the discontinuous variation can have significant effects on the Stoneley wave propagation. However, when the Stoneley wavelength is con- siderably large compared to the scale of heterogeneity variations, the Stoneley wave is sensitive only to the overall fluid transmissivity of the formation heterogeneity.

To demonstrate the effects of heterogeneity on the Stoneley wave p rop agation, an experimental data set (Winkler et d., 1989) has been modeled. The heterogeneous permeability model results agree with the data very well, while the data disagree with the results from homogeneous permeability models.

16

The numerical technique for calculating Stoneley wave propagation across permeability heterogeneities has been applied to interpret the acoustic logging data across a heterogeneous fracture zone (Paillet, 1984). The modeling technique, in conjunction with a variable permeability model, successfully explains the non-symmetric pattern of the Stoneley wave propagation, while it is difficult to explain the data using a homogeneous permeable zone model. The technique developed in this study can be used as an effective means for characterizing permeability heterogeneities using borehole Stoneley waves.

Atomistic View of Low-Temperature Ffuid-Mineral Reactions: Chemistry, Reaction Mechanism, Diffusion, and Kinetics

D R Veblen (Department of Eaxth and Planetary Sciences, The Johns Hopkins University, Baltimore, MD 21218; 410-516-8487; e-mail: [email protected])

Mineral-fluid reactions may be divided into two broad categories: (1) surface reactions at grain boundaries and (2) internal reactions. It has long been known (e.g., Lapparent, 1909) that, at the relatively low temperatures relevant to processes such as weathering and alteration of silicates, internal reactions are volumetrically more important than surface reactions. In either case, it is essential to establish the reaction mechanisms and pathways using microscopic techniques, as well as the chemical compositions of reactants and products, in order to assess mass balances between a reacting crystal and the surrounding fluid. Furthermore, if experimental and natural reaction mechanisms are different, experimental data on reaction stoichiometry and kinetics may be irrelevant to real soils and rocks.

Some internal reactions (e.g., feldspar weathering and alteration) typically do not entail an intimate structural relationship between reactant and product. In this case, inferences about the volume change during the reaction are necessary to calculate the influence of a reaction on fluid composition. Reactions involving sheet and chain silicates, however, commonly proceed via layer-by-layer topotactic mechanisms, for which the chemical ramifications of the mction can be calculated directly. In Fe-bearing silicates, heterogeneous electron-transfer reactions can be important, paaicularly for demobilization or remobilization of toxic and ore-forming metals.

The kinetics of internal reactions are dependent in part. on intracrystalline diffusion rates. Whereas bulk diffusion mechanisms are important for many high-temperature processes, chemical transport in most low-temperature reactions is probably controlled by diffusion along crystal defects. Defect-conmlled reactions have been studied intensively in metals and other synthetic materials, but earth scientists also should recognize the relationships that exist among changes in fluid composition, defect mechanisms of mineral alteration, diffusion pathways during reactions, and reaction kinetics.

Basin-Scale Permeability: Examples from three

)< BelitZ, (Dept of Earth Sciences, Dartmouth College,

J.D.Bredehoeft, (U.S.G.S, Menlo Park, CA, 94025)

Numerical simulation of modernday topographically-driven groundwater flow systems provides a framework for estimating the permeability of basin-scale aquifers and confining layers. Three such basin-scale models have been developed: the Denver Basin and adjacent midcontinent (-650,000 sq km and up to 4 km deep); South Dakota (-250,000 sq km and up to 1.5 km deep); and the Bighorn Basin (-30,000 sq km and up to 6 km deep). In all three areas, shales of Cretaceous age separate the aquifers from the overlying water table.

Oil-field and water-well data provide estimates of permeability and head for the regional aquifers. The data indicate that sandstone permeabilities range from 1 millidarcy to 1 darcy, and show a consistent relationship with depth. Estimation of the basin-scale permeability of the shale confining layers is less direct than that of the aquifers. However, the basin-scale permeability can be evaluated by

North American Basins

Hanover, NH 03755; 603-6463365)

modeling: i f the water table is taken as a specified head boundary condition and i f the permeability and hydraulic head distributions of aquifers are taken as knowns, then a model can be calibrated as a function of confining layer permeability. The numerical models indicate that basin- scale permeability of the Cretaceous shales ranges from 1 to 100 nanodarcies within the Denver Basin, from 1 to 100 rnicrodarcies in S.Dakota, and exceeds 100 microdarcies in the Bighorn Basin. The values in the Denver Basin are consistent with laboratory consolidation tests, and the relatively high values in South Dakota and the Bighorn Basin can be attributed to fracturing and faulting, respectively. These results are of value for constraining paleohydrologic models in similiar settings.

Hot Mineralking Brines in a Thin Irish Basin - Results of Simulating the Fluid-Flow System, and Lessons about Modelling

H Lewis, G D Couples (Department of Geology and Applied Geology, University of Glasgow, Glasgow G12 8QQ UK; +44 (OM1 339 8855; fax: +44 (OM1 330 4817; email: [email protected])

The very thin (Mississippian) Midland Basin of central Ireland contains lead-zinc ores precipitated from hot fluids. These deposits formed near the paleosurface at about 250'2, and they are generally thought to be syndepositional or early postdepositional. Did the hot fluids originate in thii basin?; were they transported from the deeper Munster Basin to the south?; and/or was the basement involved in generating hot fluids? We assess both the geologic issues and the difficulties of modelling this coupled heat- and fluid-flow system.

Assessing the size and character of the fluid system requires geometric knowledge of both the basin and its basement during mineralisation. Reconstruction reveals a tilted fault-block structural style with Lower F'aJaeozoic rocks (acting as basement) overlain by partially-folded, partially-faulted Mississippian strata. 2-D coupled heat- and fluid-flow models suggest that topographicallydriven longdistance flow, either within the Midland Basin, or from the Munster Basin to the Midland Basin, is insignificant. But, both basement fluid circulation and topographicallydriven local flow from a (small) uplift are feasible. Basement circulation (convection) can bring hot (2OO+C) fluids to the near-surface, but models where the circulation remains within the basin are too cool.

Combining these fluid flow models with mass-balance calculations of the metal that each system can transport, we conclude that local flow can provide neither enough metals nor sufficiently hot fluids. Basin-only flow can provide adequate metals but not the required temperatures. Basement flow can provide both the metals and adequately hot waters.

The modelling difficulties in thii situation include: modelling a markedly 3-D system, with 2-D tools; accounting for changes in the size of the real flow system with time, and properly allowing for flow changes with time when using a steady-state calculation engine.

In-Situ Study of Physical Mechaniims for Permeability Changes Associated With the 1989 Loma Prieta Earthquake

S. Rojstaczer (Department of Geology, Duke University, Durham, NC 277084230; 919684-3159; email: [email protected]) S. Hickman (US. Geological Survey, MS977, 345 Middlefield Rd., Menlo Park, CA 94025; 415-3294807; email: [email protected])

The 1989 Loma Prieta, California, earthquake (M - 7.0) caused significant changes in the shallow hydrology of the nearby Santa Cruz Mountains. These changes, which consisted of streamflow increases that persisted for several months after the earthquake and long-lived post-seismic lowering of the water table, are most readily explained by earthquakeinduced permeability increases in the near-surface aquifers and aquitards. TO test thii hypothesis and determine the physical mechanisms responsible for this presumed permeability enhancement we are conducting measurements of stress and natural fracture orientation in an approximately 170-mdeep

17

I . . borehole drilled on top of a granodiorite ridge within the Santa Cruz Mountains.

Borehole televiewer and television logging in this well has revealed numerous fractures and faults with thicknesses of up to several cm. The great majority of these fractures and faults strike N-NW and dip 40-700 to the east. We have conducted four hydraulic fracturing stress measurements in this well at depths of 30-100 m. Analysis of these data show that the magnitude of the least horizontal principal stress (Shmin) is equal to or slightly less than the calculated vertical stress (Sv) and that the direction of the maximum horizontal principal stress (SHmax) is NlOoW 200. This SHmax direction is parallel to the ridge axis (suggesting topographic control of the stress field) and the strike of most of the natural fractures and faults in this well. Thus, these fractureslfaults are favorably oriented for normal faulting. Analysis of the potential for frictional failure on these planes using simple frictional faulting theory indicates that normal faulting could be induced at this site by a reduction in Shmin of about 0.5-1.0 MPa. Simple calculations of dynamic 6.e. strong-ground-motion induced) stress ptur&tions expected during the 1989 Loma Prieta earthquake indicate that cyclic reductions in Shmin of this order are indeed possible at this location. Thus, we propose that these features represent shallow normal faults reactivated by earthquake-induced dynamic stress perturbations and that these faults, in turn, are responsible for the inferred coseismic permeability enhancement associated with the Lorna Prieta earthquake, Fuare measurements of hydraulic conductivity on fracture and fault zones in this well will further test this hypothesis.

Methods for Coupling Information about the Genesis of Geologic Features to the Development of Hydrologic Models

Jane C.S. Long and Christine Doughty (both at Lawrence Berkeley Laboratory, Berkeley, CA 94720; 5 10-486-6697, e-mail: [email protected])

Kevin Hestir (Utah State University, 801-797-2826)

The nature of fluid flow and mass transport in the earth's crust is governed by heterogeneity and anisotropy in hydrologic properties. These properties are in turn determined by the geologic origin and history of the material. The development of accurate predictive models for fluid flow and transport often requires including information about the distribution and interconnection of permeable features. It may be that some of this information can come from an understanding, even a partial understanding, of how the geologic features formed. Our work has centered on the interpretation of hydrologic well test data. We have developed a series of inverse methods which create models that mimic observed well test data. That is, we find patterns of high and low permeability or panems of conductive fractures by searching through many possible patterns until we find ones that can mimic the observed hydrologic responses. However, hydrologic data alone is not enough to constrain these inverse solutions to a unique result and we must examine an ensemble of possible results to determine how much information the well test data is really providing. If we know something about how the features form, we can constrain the search to finding patterns that mimic the growth process or observed geologic relationships. For example, we can invert hydrologic data from a fractured rock by growing a series of fracture patterns using mechanically based random fracture growth rules calibrated to observed fracture patterns. We then find a solution to the inverse hydrologic problem by conditioning the random growth on observed hydrologic response. This gives an inversion based on observed information and a mechanical understanding of fracture genesis. In fluvial systems, we can often use geological mapping to infer paleochannel characteristics such as flow Man, @en& and channel dimension. We can then apply recent fluvial geomorphological studies of river evolution to develop simple d e s for choosing appropriate values for the orientation. extent, and connectivity of high-permeability sand bodies in the subsurface. Additionally we can crate low-perm&ility structures at the lateral or lower margins of sand channels to represent overbank or mudclast deposits, respectively. The N I ~ S for sand- body creation contain stochastic parameters that can be varied in an inverse method so that the model reproduces well test data.

Effect of Mineral Reactions on Porosity and Permeability Development in Contact Aureoles

L P Baumzartner, M L Gerdes. G T Roselle, (De@ of Geology &

M A Person (De@ of Geology, Univ. of Minnesota. M m p o l i s , MN Geoph$ics. Univ. of Wisconsin. Madison WI 53706)

55455)

A two-dimensional finite element code has been developed which fully couples variable-density fluid flow with conductive and convective heat transfer. The code considers the effect of natural lithologic heterogeneities by using random but spatially correlated permeability values generated by the turOing bands method. In sharp contrast to models of free convection with homogeneous media, these heterogeneous simulations predict extreme focusing of flow around localized high pemeability zones. The symmetrical fluid flow patterns predicted by homogeneous simulations are completely obliterated.

This result clearly shows that permeability and porosity distribution as a function of spatial and temporal coordinates has to be b w n in order to describe realistically the evolution of a hydrothermal system amund intrusions. The nature of porosity in high temperature rocks has been the basis of much speculation. because any porosity generated in the mck can be expected to be rapidly eliminated by ductile deformation if fluid pressure is lower than lithostatic pressure,. Mineral textures will be presented documenting local palea-porosity. Observed porosities range from grain boundary u) centimeter- scale. Most of the larger cavities were formed by reaction of infiltrating fluids with the rock. Refractory minerals often rimmed these cavities, preventing their collapse. At a later time these cavities were filled by low-temperature mineral precipitates.

Several, in pan obvious, conclusions are drawn from this study: a) permeability and porosity measurements performed on samples collected from contact aureoles do not represent conditions during fluid flow; b) permeabilities are extremely spatidly hetemgeneous and strongly timedependent; and c) reaction-induced permeability is a fimt order effect in these low permeabiity rocks. Thus any hydrologic model that a m p t s to realistically describe fluid-rock interaction at moderate to high temperatures needs to address the permeability changes resulting from the coupling of fluid flow and mineral reactions.

Geochemical and Model Observations on Thermal, Topographic. and Mechanical Components of Fluid Flow in the Southern Alps.

P. 0. K m s , P. Upton, I). Craw (all ac Dept. of Geology, University of Otago, Box 56. Dunedin, New zealand)

C. P. Chamberlain (Dept. of Earth Science, Dartmouth College, Hanover N.€L U.S.A. 03755)

In an actively deforming two-sided orogen, fluid driving forces arise from topographic and thermal gradients as well as from coupling between deformation and fluid flow. The gross thermal and topographic driving forces imposed upon a temperatwedependent permeability structure produce a predictable flow pattern within a model omgen. However, field observations and oxygen isotope analysis of rocks from the high-&let region of rapid uplift in the Southern Alps of New Zealand indicate inadequacies in the permeability model.

Laser analysis of foliation-parallel quartz veins from the Alpine Fault trace and adjacent Alpine Schists show systematic variation of S'*Oquam values. Within the fault trace, S%(l.ara d u e s from individual mylonitic veins show a slight variation of up to 1%. In contrast, systematic variation up to 2.4% exists within individual segregations from outside the fault zone with the 61'809um values becoming lower towards rhe tips of the quartz SegregatlonS.

Lowering of S180qum is compatible with penetration of meteoric waters into ductilely deforming rocks outside of rhe fault mce to %Ian below sea level.

Numerical models of coupled mechanical-fluid behaviour which permit penetration into ductile rocks m limited to those which produce a dynamic permeability through transient, dilatant mechanisms. The coupled flow paths and rates for dilatant, strain- dependent rheologies prcduced in the numerical models are compatible with those interpreted from the geochemical and field data from the Southem Alps.

18

Wednesday, June 8, 1994 Evening FractureControlled Fluid Flow and Mass Transport in the Mid-

dle and Lower Crust J 3 Ague (Dept. of Geology and Geophysics, Yale University,

P.O. Box 208109, New Haven, C T 06520-8109; 203-432-3171) Fracturing can significantly increase the porosity and permeability of metamorphic rocks, and thus influence crustal mass and heat transport. Evidence from geophysical studies strongly suggests that fracturing is common at middle to lower crustal levels in orogenic belts. For example, from 4/80 through 2/94, 1076 seismic events were recorded at depths of 20-35 km in southern California (data from the Caltech Earthquake Catalog). Petro- logic study of quartz veins and their wallrocks from the Wepawaug Schist, CT, constrains the role of fracture flow in the petrologic evolution of staurolite and kyanite zone pelites at depths of 20- 30 km. Measured vein density is about 20-30 percent, The veins are commonly surrounded by an aluminous selvage that is rich in staurolitefkyanite and micas, and poor in quartz and plagioclase. Staurolite and kyanite we generally absent from the wallrocks located beyond the selvage margins. Because crack-seal textures are widespread in veins, vein development was almost certainly episodic. Four independent lines of evidence suggest that the quartz veins represent zones of major regional metamorphic fluid flow. 1) Mass balance analysis indicates that major and trace elements were mobilized during selvage formation by reactions that destroyed quartz, plagioclase, and micas, and produced staurolite and kyanite. 2) Estimated f H c l / f x , o is highest in the selvages, which suggests that the most altered rocks were infiltrated by fluids with elevated fHcl/fFzo, and that the avenues for infiltration were quartz veins. 3) Silica loss from local pelitic wallrocks can only account for -70 percent of the volume of quartz in the average amphibolite facies vein. The other 30 percent is inferred to have been externally-derived via fluid infiltration down regional T and P gradients. The estimated time-integrated fluid flux averaged over the entire exposure area is - 6 x lo4 m3 m-2. This flux may have been sufficient to cause advective heat transport. 4) Previously published stable isotopic studies suggest that the fluid that precipitated vein quartz was in part externally-derived. It is concluded that widespread syn-amphibolite facies quartz vein development and associated staurolite and kyanite.grodh may mark regions of major fluid outflow and advective heat transport in orogenic belts.

Session V: APPLICATIONS OF GRID SCALE PARAMETERS IN MACROMODELS

Integration of Hydrostratagraphic Data in Reactive Transport Models

Carl W. Gable; George Zyvoloslti, Bruce Robinson @a& and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos NM 87545. Internet: [email protected])

With the growing availability of large hydrologic and geologic data bases, the task of incorporating data into hydrologic flow and transport models can be very complex. We wish to incorporate as much available data as possible, however the task of setting up computational problems can become quite formidable. As part of an effort to produce more accurate models of liquid and vapor and contaminant movement, we have developed software for generation of unstructured finite element and structured finite difference meshes utilizing well log and hydrostratigraphic data. The mesh generation capability, which insures an optimal Deleany mesh, allows us to automatically and accurately represent the complex hydrostratigraphy, topography, faulting, intrusions and other complex geometries encountered in geologic formations.

For many applications, understandingthe movement of a contaminant is the prime motivation for modeling. In this work the travel time of radionuclides to the accessible environment is the contaminant of interest. The flow of vapor and liquid phases will determine flow trajectories, and decay and sorption characteristics of radionuclides play key roles in retarding movement. To study the sensitivity of retardation to sorption and decay, we first calculate a steady state flow field. Radionuclide migration calculations are used to explore the sensitivity of migration times to transport parameters. For these calculations the convectivedispersion equations are solved with sorption and radioactive decay. Sorption is modeled assuming equilibrium sorption, with linear or nonlinear sorption isotherms. Radioactive decay is modeled assuming -an irreversible, first order reaction with rate constants adjusted to achieve the half-life of radionuclides in question. Parameter sensitivity analyses have focused on effects of sorption Kd values on times required for a given percentage of the radionuclide to reach the water table below the release zone (we refer to this time as the transit time below). Kd is set to a non-zero value in one stratigraphic unit and 0 elsewhere. The source term is modeled as a mne of constant concentration for a short time, after which radionuclide migration is integrated to obtain a transit time. In a series of runs where Kd is non-zero in different stratigraphic units, the transit time is determined, thereby assessing the relative importance of obtaining accurate laboratory measurements of Kd in each of the units. Calculations of this sort for the migration of Neptunium are discussed.

Is it Possible to Use Mineral-water Reaction Rates from Laboratory Measurements to Quantify Chemical Evolution in Natural Systems?

S.L. Brantley (Department of Geosciences, Pennsylvania State University, University Park, PA 16802,814-863-1739, email: [email protected])

Geochemists interested in quantification of mineral dissolution and precipitation have documented that rates of mineral-water reaction in MtUral systems are slow compared to the rates measured in the laboratory. If disparities between laboratory and field rate estimations could be reconciled, mineral reaction kinetics could be used to constrain models of fluid flow in soils and aquifers.

The mineral-water interfacial area in natural systems is perhaps the most difficult parameter to estimate in extrapolating from laboratory to field.

Where multiple phases dissolve and multiple reactions can be quantified, the rate of reaction of one phase can be assumed and all other reactions scaled to that phase. Making such an analysis depends upon the availability of large data sets of mineral reaction kinesics and mechanisms undex varying natural conditions, as well as information about the lithology of the aquifer. At present, the quality of the available database is extremely variable, and the laboratory rates need to be tested in more natural systems.

For example, analysis of the rates of feldspar dissolution in aquifers and soils reveals that feldspar dissolves more slowly in the field than-in the laboratory. However, recent laboratory work shows that ~nany laboratory experiments were not allowed to progress to true steady state, and feldspar dissolution is actually slower than previously reported. As the kinetic database for feldspars and other minerals is amplified, improved, and tested, the use of geochemical kinetics to quantify such parameters as water-rock interfacial area and fluid residence time may become possible. Testing of laboratory rates in well-constrained field systems with few reactive mineral phases is also sorely needed.

Tracing Active and Ancient Groundwater Flow Systems Across the Cooper & Eromanga Basins, Australia using Mathematical Modeling and Geothermal Data.

Mark Persoq, @epartment of Geology & Geophysics, University of

Denah Toupin (GEI Consultants, Inc., 1021 Main St., Winchester,

Peter Eadington (CSIRO, Division of Petroleum Resources, P.O.

Dave Warner (Santos, Ltd., 101 Grenfell St., Adelaide, SA 5000

Minnesota, Minneapolis, MN 55455; 612-625-7332; [email protected])

MA01890)

Box 136, North Ryde, NSW, 21 13 Australia)

Austdia) The Cooper and Eromanga Basins, Australia have one of the

largest and best documented regional groundwater flow systems in

19

the world spanning nearly 1500 km in length. While the present-day hydrology of the Jurassic and Cretaceous aquifer systems are reasonably well documented, little is known about how groundwater flow patterns have evolved through time. Even less is understood about how circulating pore fluids have affected subsurface thermal processes. Previous attempts to deduce the thermal evolution of these basins using fluid inclusion and vitrinite reflectance data as well as apatite fission track analysis have yielded equivocal results.

The approach taken in this study has been to compare mathematical models of groundwater flow, heat transfer, and the thermal evolution of sediments with detailed field observations including: resent-day geothermal gradients, groundwater age dates based on %Cl, fluid inclusion and vitrinite reflectance data, and apatite fission track annealing data. Two cross-sectional, finite element models of compaction- and topography-driven flow were constructed along transects through the basins that more or less follow the present-day groundwater flow directions.

Quantitative results suggest that Tertiary and Pliocene uplift events within the central and eastern portion of these basins induced two episodes of regional groundwater flow that had a pronounced effect on paleoheatflow. Convective heat transfer effects produced up to 40 OC temperature anomalies across the basin. While calculated flow patterns are in good agreement with present-day geochemical, hydrologic, and thermal data, and are consistent with paleogeothermometric information, evidence for the hydrologic evolution of the Cooper and Eromanga Basins is ambiguous due to these basins complex tectonic and hydrologic history.

Multicomponent Reactive Solute Transport in Physically and Chemically Heterogeneous Aquifers

S David Sev-, Steven B Yabusaki, Carl I Steefel and Timothy D Scheibe (all at: Battelle, P a d c Northwest Laboratories, P.O. Box 999, Richland, WA 99352; (509) 375-4498)

Reactive solute transport in a subsurface setting characterized by multiple spatial-scale physical and chemical heterogeneities is a significant challenge in hydrogeologic modeling. At issue is how the local coupling of reaction kinetics and material heterogeneities at the pore or meter scale influences contaminant transport at the field or basin scale. Previous work in this area has examined the displacement of contaminant plumes in statistically homogeneous, random conductivity fields with retardation controlled by equilibrium sorption reactions. This research examines retardation caused by kinetically-limited precipitatioddissolution reactions in a detailed synthetic conductivity field that includes commonly observed subsurface geologic structures. These synthetic, but realistic, data sets preserve many structural features and much of the conductivity connectedness that is lost in statistically generated conductivity fields. Fickian dispersion models were found to be insufficient for nonreactive contaminants, and we examine the extent to which this ObSeNatiOn s t i l l holds in the presence of both kinetically controlled reactions and varying degrees of chemical heterogeneity.

One of the most important influences on the large-scale breakthrough behavior of contaminants is, the degree of spatial correlation between the chemical properties (such as reactive surface area and mineral volume fraction) and the conductivity. We examine a range of correlation from positive to negative and the resultant change in the shape and velocity of the contaminant plume. Through its effect on the "local" precipitatioddissolution rate, the variability in reactive surface area coupled to the variability in "local" conductivity produces differing degrees of reaction front sharpness at various points in the medium. These local reaction fronts interact in a complicated fashion to produce an overall displacement pattern, which may or may not be accurately duplicated by simple scale-averaging of the chemical and physical properties. Simulations are carried out on massively parallel computer architectures to resolve the influence of multi-scale heterogeneities on multicomponent, multi-dimensional reactive transport.

Work was supported by funds from the Environmental and Molecular Sciences Laboratory at Pacific Northwest Laboratory.

Basin Scale Modeling of Coupled Hydrogeological and Mechanical Processes

Shemin Ge (Department of Geological Sciences,University of Colorado, Boulder, CO 80309, 303-492-8323, e-mail: [email protected])

As a component of coupled hydrogeological processes, hydrogeological and mechanical interaction in the earth's crust has a direct association with several geologic phenomena such as thrust faulting, fluid-injection induced earthquakes, and tectonicallydriven fluid migration. Although the theoretical basis for the development of coupled mechanical and hydrogeological models can be traced back to the concepts of effective stress and soil consolidation by Terzaghi in 1923 and the significant advancement by Biot in the 1940% the major geological application to fluid-related structural displacement problems occurred in 1959 when Hubbert and Rubey recognized that fluid pressures can reduce the frictional resistance of rock to induce thrust faulting. In the past decades, some analytical and numerical models have been proposed to study a variety of processes in more complicated geologic settings involving deformable environments. As a result, our general understanding of the coupled phenomena in geological processes has been greatly enhanced.

As we are heading towards tackliig more complicated hydrogeological phenomena, it would be logic to better understand where we stand now, what are the major limitations in the previous studies, and the challenging tasks ahead of us. These questions will be addressed through examining some existing models such as the coupled fluid flow and rock deformation model describing tectonically-induced fluid flow in sedimentary basins. This model is based on poroelasticity theory and applies elastic-plastic slip element technique to account for large deformation around a fault, while the surrounding rocks are represented by continuous poro-elastic media. Simulation results show that tectonic compression will cause pore pressure to arise near loading fronts and the area beneath a low permeable fault. The elevated pore pressures, in turn, will set up a transient flow system, which suggests that episodic tectonic activities may have caused episodic transient subsurface flow in the geologic history.

Impoitance of Geometry in Simulating Groundwater Systems - Examples from Hydrocarbon Exploitation, Minerals Genesis, and Environmental Protection

F D C o u ~ l ~ . R S Haszeldine, D Darby, C G Fleming, H Lewis, C McKeown, R N T Stewart (Deparbnent of Geology and Applied Geology, University of Glasgow, Glasgow G12 8QQ UK; +44 (Ow1 339 8855 x 6860; fax i-44 (Ow1 330 4817; email: [email protected]

m e basin analysis research programme at the University of Glasgow has investigated the geohistory of a number of settings in which groundwaters have played a key role. We have studied cases where groundwaters have: (A) been static for a long time; (B) undergone substantial motion and/or replacement; (C) contributed markedly to the thermal state; (D) been shown to be a risk in the dispersal of radioactive waste; (E) transported solutes [with precipitation andlor leaching of diagenetic minerals or economic metals]; or 0 exerted an important mechanical influence [in overpressured fells]. Throughout these studies, the recurrent "theme" is that of geometry - the geometry of the rocks, the geometry of the energy system(s), and the geometry (distribution) of fluid types.

In this talk we will emphasise the importance of geometric aspects in basin modelling via studies including: (1) Localisation of carbonate concretions in N Sea P a l m e sands due to mixing of hydrocarbons and basinal fluids with influxing meteoric waters; (2) Diagenetic histories of several N Sea reservoirs which indicate a variety of hydrogeologic behaviours; (3) Locations and causes of overpressure in the N Sea; (4) Modern temperature anomalies (>4OC) in the N Sea Central Graben and their relationship to fluid flow; (5) Quantification of thermal and fluid budgets for Carboniferous mineralisation in the Irish Midlands; and (6) Assessment of the hydrogeology of the proposed Sellafield nuclear waste repository.

20


Thursday, June 9,1994 Morning

Transport Properties of Single Fractures

Stephen R. Brown (Geomechanics Department 61 17, Sandia National Laboratories, Albuquerque, NM 871854751)

Detailed study of natural fractures in rock indicates that the surfaces of an individual fracture are rough and mismatched with one another at small length scales and are nearly parallel at larger length scales. Thii leads to the important prediction that there is an upper limit to the scale dependence of the physical properties of a single fracture, which can be thought of as the 2dimensional equivalent of a representative elementary volume (REV). The length scale below which the surfaces become mismatched is typically smaller than a centimeter. Computer simulations of the transport properties of a single fracture show that the transport properties of rough-walled fractures deviate significantly from the commonly used parallelglate model of a fracture.

The solutions for the transport properties were obtained essentially by considering the variation in hydraulic and electrical conductivities in the fracture plane as random 2-D resistor networks. In an effort to reduce the problem to as few free parameters as possible, the results of these simulations have been reevaluated in terms of some results of “effective medium theory,’’ “real-space renormalization,” and “percolation theory”. Both effective medium theory and realspace renormaliation give excellent approximations to both the hydraulic and electrical conductivities over a wide range of surface separations. However, the conductance of the critical path as given by percolation theory is typically a much poorer approximation.

The success of effective medium theory is significant, since it depends only on the probability density function of the fracture aperture, which if Gaussian depends on two parameters: the mean anastandard deviation. An extension of the analysis by Wang et al. [JGx: 93,2216-2224, 19881 for the contact of two mirror-image fractal surfaces under shear of& gives the standard deviation of the apercure as a function of the sampIe length, topothesy (roughness scaling parameter), fractal dimension, and shear offset. Combining these two results explicitly gives the general dependence of both the hydraulic and electrical conductivities of a single fracture on five free parameters: the mechanical aperture, sample length, topothesy. fractal dimension, and the shear offset.

This work was performed at Sandia National Laboratories supported by the U.S. Dept. of Energy under contract no. DE-AC04-94AL85000.

Hydraulic Conductivity of Fractured Crystalline Rocks From Meter to Kilometer Scale: Observations From the Mirror Lake Site, New Hampshire

354-3324: e-mail: [email protected])

5884; e-mail: [email protected])

9008; e-mail: [email protected])

354-3372; e-mail: [email protected])

P A Hsieh (U.S. Geological Survey, Menlo Park, CA 94025; 415-

A M Shapiro (U.S. Geological Survey, Reston, VA 22092; 703-648-

D J Goode (U S Geological Survey. Malvern PA 19355; 215-647-

C Tiedeman (U.S . Geological Survey, Menlo Park, CA 94025; 415-

Hydraulic conductivities of fractured crystalline rocks in the vicinity of Mirror Lake in cenrral New Hampshire were determined on 3 scales (several m, 100 m, and several km) by three methods (single- well hydraulic tests, multiple-well hydraulic tests, and calibration of a ground-water flow model, respectively). Using two packers to straddle 4.6-m test interval, 200 single-well tests were performed in 11 wells that penenate 83 to 216 m of rock in a 1 km by 1 km m a . These tests yield hydraulic conductivities that characterize the rock within several m of the well. Test results show that hydraulic conductivity varies over at least 5 orders of magnitude, from below

2

1 x 10“’ m/s (lower limit of measurement of test equipment) to 5 x loJ 4 s . Within each well, there are several test intervals where the hydraulic conductivity is 3 to 5 orders of magnitude greater than the that of the remaining intervals. To determine hydraulic conductivity at the next larger scale, multiple-well hydraulic tests were performed in a 120 m by 80 m well field where 13 wells were drilled to investigate the upper 60 rn of rock. Test results show that the mck underlying the well field contains 4 highly conductive fracture clusters, each cluster occupying a near-horizontal, tabular volume approximately 1.5 m thick by 20 to 50 m in horizontal extent, with a hydraulic conductivity of 6 x loe5 ds. These highly conductive fracture clusters are hydraulically connected to each other via a less conductive fracture network having horizontal and vertical hydraulic conductivities of 3 x lo-* and 2 x IOm7 m/s respectively. Numerical simulation of flow in the well field suggests that the equivalent (bulk) hydraulic conductivity of the 120 m by 80 m by 60 m block of rock is 2 x conductivity of 5 x 4 s obtained by calibrating a 3-dimensional ground-water flow model covering a 3 km by 3 km area to a depth of 150 m in the rock. The similarity suggests that the hydraulic conductivity distribution determined at the well field could be representative of the larger modeled area. Taken together, results from the Mirror Lake sire suggests that, on the scale of several meters, hydraulic conductivity varies over many orders of magnitude; on the scale of 100 m, the hydraulic conductivity distribution consists of several highly conductive fracture clusters embedded within a less conductive fracture network; on the scale of several km, it is the less conductive fracture network that controls fluid flow. These findings suggests that hydraulic conductivities determined at different scales at the Mirror Lake site do not follow a simple scaling law. To understand the scaling relationship, it is necessary to understand the pattern of heterogeneity at the site.

m/s: This value is similar in magnitude to the hydraulic

Fluid Flor and Transport Neal the Critical Point of H20

sEInaebritsen ( U . S . Geological Survey, Menlo Park, CA

D 0 Hayba (U.S. Geological Survey, Reston, VA 20092)

94025; 415-329-4422; e-mail: [email protected])

e-mail: [email protected])

Near-critical extrema in the properties of water may strongly influence flow in hydrothermal systems, but these extrema have inhibited quantitative modeling of

the critical region. Posing governing equations in terms of pressure (P) and enthalpy (H) avoids equation- of-state singularities at the critical point (22.055 m a , 373.98OC) and facilitates computation. Our numerical simulations using a P-H based model show little near-critical enhancement in heat transfer for systems in which flow is driven by fixed pressure drops. Xow- ever, in density-driven systems, near-critical variations in fluid properties can enhance convective heat transfer by a factor of 10’ or more (“superconvection”).

Two-phase sub-critical processes (“heat pipes”) can be at least equally effective. critical conditions, simulated Nusselt numbers (Nu) agree reasonably well with those predicted using the Rayleigh Number ( R a ) and the empirical relation Nu = 0.218Ra0.5.

convection or heat-pipe development the upper range of those believed typical of near-magma environments, and changes in rock rheology and quartz solubility that occur in the 350-4OO0C temperature range would tend to restrict permeability in many systems.

Therefore, superconvection may be most likely to occur in environments where high strain rates maintain pemeability despite competing processes.

Under single-phase near-

The permeabilities required for super-

m2) lie in

Hydrologic Modeling of Magmatic-Hydrothermal Systems

D 0 Hayba (959 U.S. Geological Survey, Reston, VA 22092;

S E Ingebritsen (439 U.S. Geological Survey, Menlo Park, CA

Results indicate that the stochastic convective approach provides a more accurate upscaling of the ensemble reactive transport behavior under nonlinear reactions in heterogeneous media than that afforded by the conventional volume-averaged convection dispersion equation. e-mail [email protected])

94025; e-mail [email protected]) Pacific Northwest Laboratory is operated for the U.S. Department of b e r a by BattelIe Memorial Institute under Contract DE-ACW76RLO 1830.

Previous quantitative flow-models of hydrothermal Systems driven by cooling plutons have been unable to simulate two-phase flow or flow caused by thermal pressurization. We have developed a high- temperature program, HYDRCEHFBM, that incorporates these processes. HYDROTHFlRM is a fully transient, three-dimensional model that uses a f~te-difference approach to simulate heat transfer and multiphase flow of pure water at temperatures m&g fmm 0" to 1200°C and PreSSURS from 0.5 to 10,m bars. The governing equations are expressions of mass and energy conservation expressed in terms of pressure and enthalpy.

For our initial examination of magmatic-hydmthermal systems, we evaluated the effects of host rock permeabity (mging from l 8 I 4 to l ( r I 8 m2) and depth of pluton emplacement (2, 2.5, and 3 km). We assumed a 900°C pluton (2.5 km high by 1 fan half-width) instantaneously intmded into an homogeneous and isotropic, two- dimensional medium with an initial 20"C/km geothermal gradient. The sides and base of the model were impermeable and insulated, and the top boundary was held constant at 20°C and 1 bar. For a host permeability of sides of the pluton so rapidly that temperatures in the hydrothermal plume above the pluton rarely exceed 200°C at depths less than 1 km, regardless of the depth of emplacement. At intemediate permeabilities, lo-'' m2, temperatures approach 300°C at a depth of 1 km, and two-phase flow develops in the hydrothermal plume. The extent and duration of two-phase flow depends on the level of emplacement. A pluton at 2 km generates a two-phase geothermal system that persists for several thousand years. For low perme abilities, 5 m2, oonduction dominates and the maximum temperature at 1 km depth is only 170°C for the shallowest intm sive. ~t permeabfities of m2, thermd pmurization causes fluid pressures to increase significantly above hydrostatic for 10,OOO years, and at permeabilities of lo-'' m2, pressures exceed lithostatic.

Permeability Scaling in a Numerical Aquifer

T D Scheibe and S B Yabusaki (Both at Pacific Northwest Laboratory p.0. Box 999, Richland, WA 99352)

m2, heat is advected from the top and

Permeability and dispersivity in aquifers characterized by multiscale heterogeneities in material properties aredependent on the resolution, scale, and boundary conditions of a posed problem. This dependence is typically not well defined; consequently, the specification of these parameters in a modeling analysis is problemmatic.

We perform computational experiments to investigate how highly detailed, fine scale permeabilities might be averaged to best retain flow and transport behavior at coarser grid scales. The baseline for this study is a simulation of flow and transport through a three-dimensional distributionof fine scale permeabilities synthesized from sedimentological features observed in point bar sediments from Indiana's Wabash River. 16,777,216 grid cells are used to resolve multiscale heterogeneities present in the permeability data set. Massively parallel computers provide the memory and computational performance to investigate this scaling problem.

Permeability upscaling (i.e., calculating equivalent conductivities at larger scales to represent bulk flow behavior) is performed at a variety of grid scales using a global power law averaging technique. A series of tests are performed to determine the optimal scaling exponent at each scale for a number of metrics (e.g., total flow, aquifer potential, velocity, arrival time and position). Results are compared to alternative scaling methods found in the groundwater literature. The simulations clearly show that transport is strongly impacted by the existence and connectedness of extremekdued hydraulic conductivities.

Session VI: SCALING RELATIONS

Stochastic Convective Transport with Nonlinear Bioreaction in Heterogeneous Medii

T R Giu, C S Simmons, B D Wood and E M Murphy (All at Pacific Northwest Laboratory P.O. Box 999, Richland, WA 99352)

mere is as yet no consistent way to upscale nonlinearly reactive transport in heterogeneous media through the conventional vol~s-averaged convection dispersion equation (CDE). A stochastic convective transport method is developed for one dimensional transport in physically heterogeneous media with nonlinear reactions. The method circumvents the scale dependence of phenomenological parameters by representing the transport as an ensemble of independent convective-reactive streamlines, each characterized by a randomized convective velocity (or travel time) The overall transport behavior is obtained as the average of the streamline convection reaction patterns over the corresponding travel time probability distribution function. The method provides for separable scaling of the physical transport and reaction processes in a way that captures the l a r g d e effects of the nonlinear reactions without resort to effective constitutive parameters.

The approach is used to simulate the fate and transport of bioreactive substrate in a binary inclusive (matrixsupported clastic) heterogeneous field, in both Monte Carlo analysis of a specific synthetic ensemble of transport fields and in intermediate scale experiments. Clastic heterogeneity is representative of many glacial/fluvial depositional environments and induces both complex mechanical solute dispersion as well as evolving microbial heterogeneity doe to spatial variability in the geochemical environment.

Pacific Northwest Laboratory is operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.

Simulation of Reactive Contaminant Migration in Physically and Chemically Heterogeneous Soils

A. F. B. Tomson (Lawrence Livermore National Laboratory, PO Box 808. Livermore, CA 94551; 510-422-6348, afbt@llnLgov)

A. Schafer-Perini and R W. Smith @G&G Idaho, Idaho National Engineering Laboratory, Po Box 1625, Idaho Falls, II) 83415)

Large-scale rates of migration, dilution and transformafion of contaminant mixtures in ~tura l soils can be affected by smaller- scale heterogeneity in the physical and chemical properlies of the soil formation. Natural variation in hydraulic conductivity has long been known to accelerate dilution and spreading in aqueous contaminant plumes; associated variation in reactive soil mineral abundance or specific sorption capacity can also impact the perceived rates of migration and dilution as welL

Here, we will present preliminary, highly resolved experimental simulations of the migration of a uranium-organic acid mixture within a nonuniform sand and silt formation characterized by variably distributed metal-oxide coated materials. Here, competitive sorption of the uranium ion, acid ligand, and uranium-ligand complex onto the metal oxide surfaces will be considered within an overall heterogeneous flow framework. The overall impacts of the flow and chemical heterogeneity on multicomponent transport and dilution will be compared with traditional notions of hydraulic or reactive uniformity and noncompetitive sorption behavior.

22

Initially, characteristic (or provisional) distributions of soil properties and material heterogeneity will be developed from idealized models and published analyses of soil property heterogeneity and correlation between permeability and sorption capacity. The simulations are being used to develop plans for more specific data gathering efforts and field experimentation.

This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.

Development of Scale-Invariant Transport Laws for Groundwater Remediation Modeling

J F Pete= and S E Howington &th a t Waterways Experiment Station, Vicksburg, MS 39180; 601-634-2590, [email protected])

The central difficulty in devising new models fromexisting theory of flow and transport in porous media is that model parameters often depend on the scales at which their measurements are made. For example, an apparent scale dependency arises as a result of the macroscopic Fickian desaiption for dispersion, which is evidently a non-Fickian process. Many non-Fickian dispersion models currently proposed are non-local, wherein the rate of change of concentration in an elemental volume depends not only on a concentration gradient in the element, as for a local continuum law, but on the history of the gradient in a finite region around the element. Accordingly, the non-local form of the equation is represented in terms of convolution integrals. One may have non-local dispersion, non-local advection, etc., but each describes a different physical process.

A theoretical approach is presented based on representing a discrete porous network in terms of continuous variables. A governing equation of the non- local type results. It is recopzed that a non-local governing equation, in general, can be interpreted as being equivalent to a difference equation for a discrete system. Thus, the non-local model must be considered in light of two factors. The first factor concerns the fundamental processes modeled by the discrete system; the secund factor relates to the "dispesion" introduced by the discreteness of the system. For the model considered here, the equation reduces, in the l i t , to a traditional advective transport equation and thus, even at the continuum limit, remains non-Fickian. Note that a non-local equation will necessarily display a scale dependency not found in its local continuum counterpart. This fact, however, does not give the non- local version validity unless it also incorporates the underlying physics. Disfinguishing between the scaling effects of non-local Fickian versus non- local advection becomes critical when modeling other hydrologic, chemical, and biological processes. These concepts are illustrated by examples.

Fluid Overpressures and Hydrological Properties of the Earth Crust.

Pierre Gavrilenko & Yves Gueguen (GCosciences Rennes, Bat. 15, Campus de Beaulieu, Av. GCnCral Leclerc.35042 Rennes Cedex, France)

We examine the coupled problem of fluid overpressure build up, permeability and mass transfer in the cmst Fluid flow in the crust is described by means of an advection-diffusion quation derived from poroelastic theory. A sour& term is added to the equation which could result from different processes: porosity reduction or fluid injection. The capability of the crust to develop and maintain fluid overpressures depends mainly on the magnitude of the source term and on the permeability. We start from a permeability model based on the statistical description of a population of cracks and we assume khat permeability variation with depth is controlled both by crack closure and fracture density depth variation. We review some possible assumptions for fluid overpressure huild up in ~lic crust on this basis. First, we focus our attention on the cl'l'ect of porosity reduction. Pressure solution creep is likely to occur on asperities on cracks surfaces and this leads to a porofiity reduction. Secondly, we study the effect of a supply of fluids from the lower crust. Various set of hydraulic parameters are tested. ID simulations are performed in order to discuss the consequences of both of these processes on the physical properties of the crust. In parallel, we examine the cl'l'cct of the heterogeneous nature of the hydraulic fracture ncfwork. Computations on large scale permeability models are

pcrl'ormed. That allows to dcscrihc some aspects of fluid flow Cocuaing associatcd to a Iracturing cvcnt and givcs new insight on fluid llow regimes in thc crust.

Universality and Models of Groundwater Flow

Roger Beckie (Department of Geological Sciences, University of British Columbia, Vancouver, BC, V6T 124, ph. 604-822-6462, fax. 604-822-6088; email: [email protected])

Most often, one can only explicitly model the larger scale dynamics of geophysical processes. Indeed, one typically does not possess sufficient data to describe the properties of the system in detail, or nonlinearities inherent in the physics lead to a rich scale behavior which overwhelms one's computational ability. It is therefore important to understand the interaction between explicitly resolved dynamics and unresolved dynamics. The concept of universality is central to the interaction between dynamics on different scales and the rescaling of models.

Here, I examine when it is possible to construct an accurate model for the explicitly resolved, large scales of groundwater flow, without an explicit description of the smaller subgrid scale dynamics. I show how unresolved, subgrid scale dynamics interact with resolved scale dynamics and that a universally valid resolved scale model can be constructed if the resolved dynamics are sufficiently independent of the details of the subgrid scale dynamics. In that event, a resolved scale model is composed of a universal structure and accompanying model parameters. The model parameters represent the effect of unresolved dynamics upon resolved dynamics.

A Note on Supra-Grid Modeling of Groundwater Flow through Crystalline Rocks

Dr. Sven Follin (Dept. of Engineering Geology, Lund Institute of Technology, Lund University, P.O. Box 118,S-22100 Lund, Sweden; Fax: int+46 (46) 109127; E-mail: [email protected])

Groundwater flow through crystalline rocks was tentatively studied by examining apparent conductivity data from double-packer tests conducted in'core boreholes and performing Monte Carlo simulations of flow through highly heterogeneous porous media in two dimensions. A comparison of double-packer test data on various scales raises important questions concerning the interpretation ofthe observed scale dependence as well as about the choice of interpretation model for the inverse problem. For the sake of this study, we assumed that the observed spatial variability of apparent conductivity data on a 3 m support scale obey an statistically isotropic, lognomal random function in two dimensions with a log-conductivity variance sigma2(index:lnK) of 16. The Monte Carlo simulations yield that statistical isotropy on a subgrid scale does not necessarily imply hydraulic isotropy on supra-grid scales. Concerning the spreading of a conservative solute, we restricted our treatment to a single realization with a characteristic field dimension of 32lamda(index:lnK), where lamda(index:lnK) is the log-conductivity integral scale. The solute dispersion was studied in two orthogonal directions. Despite an isotropic log-condudivity field, different dispersivities were obtained. This result demonstrates 'that the studied realization was not large enough to provide ergodicity.

Poster Presenters: Scaling Up in Percolation Modelling for Fluid/Solute Transport

V J Homer (MS 6038, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 378314038; fax 615-576-8646, internet: [email protected]) P M Jardine and R J Luxmoore (same institution, address, and fax as above; internet: [email protected] and [email protected])

Analysis of tluid/solute transport in soil systems is complicated by heterogeneities in pore geometry that can span several orders of magnitude. The use of network models to mathematically characterize transport behavior

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&lows heterogeneities at multiple scales to be included explicitly. In particular, random-walk 3-D percolation simulations of fluid flow capture transient, non-equilibrium flow patterns important for understanding various flow/storage processes, such as in rain driven leaching from waste sites.

We are employing a percolation modelling approach to examine experimentally observed solute concentration patterns not adequately described by other available models. Although the scales of field observation vary from 4 to 380,000 square meters, vital dispersive behavior is controlled at much finer scales. Accordingly, data for percolation simulations are gathered at resolutions ranging from 10" to 10' meters, using tomography, scanning electmn microscopy, and nuclear magnetic resonance. Rather than attempting to include this wide range of length scales into a single model, our strategy is to scale up by an inductive process, expanding the percolation domain concept developed by Ewing and Gupta (W.R.R. 9. 3169-3178, 1993) to define pore networks at Successively larger scales. In our approach, output information from the network as a whole at a particular level is reduced to node-to-node input data for more coarsely resolved simulations. Parameters of interest (e.g. hydraulic conductivity) generated at model boundaries in simulations at smaller scales ,are implemented into the probability rules for simulations run at longer length scales, and are also available as inputs for finite element models. An expectation for future study will be to compare the quality of results from simulations generated by scaling up strictly within the percolation regime, to results gathered by switching from percolation to finite element models in the scaling-up process.

Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed for the United States Department of Energy by Martin Marietta Energy Syqtems. Inc.. under Contract No DE-ACU5-840R21400, and in part by a program administered jointly by ORAU and OWL.

The Thermal Effects of Fluid Flow Within the Central Graben: A Finite Element Model

C G Fleming, D D Co- and R S Haszeldine (Geology Department, University of Glasgow, Glasgow, Scotland, UK, G 12 8QQ; 041-339-8855; email: [email protected]; [email protected]; rsh@geology .gla.ac.uk)

Temperature and lithological data from forty-six wells distributed along a SW-NE section line (from the Mid-North Sea High, across the Central Graben, to the Norwegian-Danish Basin) define the modern temperature field and the geological setting of a part of the Noah Sea Basin. Derived from corrected bottomhole temperatures, thermal profiles (from two to five kilometres depth) show temperature variations of up to 72C at single depths, with significant, iocalised temperature anomalies (short wavelength, high amplitude) being associated with major fault/ fracture zones. Thermal and fluid flow modelling demonstrates that variations in thermal conductivity (e.g. basement vs. sedimentary fill), salt, or basal heat flux, are insufficient to explain the observed temperature patterns. Therefore, another mechanism of heat transfer must be operating within the basin. A basin-wide two-dimensional section from the Pennines in England to Southern Norway is modelled using OILGEN (a package designed by Prof. Grant G w e n of Johns Hopkins University). These steady-state finite element method computer simulations yield temperatures matching the observed pattern when fault zones are explicitly included as potential flow conduits. Episodic (transient) fluid flows might produce even sharper temperature anomalies. Such transient flows could be the result of episodic release of overpressure.

Implications of the Biothm Appmach (Biostratigraphic Analysis) to Large-Scale Hydrogeologic Simulations

(Department of Geology and Applied Geology, Univ of Glasgow, Glasgow G12 8QQ UK; -1-44 (OH1 339 8855; fax: +44 (0)41 330 4817; email: [email protected], [email protected],ac.uk), M W Frye (The MITRE Corp. 7525 Colshire Dr, M c h VA 22102; (703) 883 7826), H R Lane (AMOCO Production Co, P 0 Box 3092, Houston, ?x 77253-3092; (713) 366 4156)

P T Dougan, D D

Our understanding of the architecture of sedimentary basins is substantially more complex than can be used in the usual numerical simulators for fluid

flow. However, "up-scaling" methods offer a technique to at least partially bridge this apparent gap. It is therefore appropriate to revisit the topic of stratigraphic correlations.

The Biothem Approach is a biostratigraphically-based method which is used to identify time-correlative (often unconformity-bounded) rock packages. If biostratigraphic control is sufficiently detailed, the sequences which are correlated by the Biothem Approach are genetically related in such a way that their internal facies (and hence their initial material properties such as permeability and porosity) are inherently consistent. The spatial relationship of one biothem to its vertical neighbours is a function of the details of the actual pattern of deposition and erosion which results from the basin's subsidence history. The resulting onlaps, offlaps, and parallelism of facies creates a complex, but rational pattern of flow units which can, in principle, be "up-scaled".

Examples from the middle Palaeozoic of North America and the Lower Teaiary of the North Sea illustrate the Biothem Approach. The Palaeozoic example, in particular, reveals a surprising pattern of uplifts interrupting basin subsidence; these should have caused considerable topographicallydriven water flows through what has been viewed as a continuous marine succession.

Palaeogeographic re-constructions are a key element in assessing the basin history as revealed by biothemic correlations. Automation of these methods is currently underway, and a progress report will be given.

Analysis of the Overpressured Central Graben, North Sea via Linked Regional Potentiometric Mapping and Pressure Modelling.

D Darby, R S Haszeldine, C G Fleming and G D Couuk (Geology Department, University of Glasgow, Glasgow, Scotland, UK. G12 8QQ; 041-339-8855; email: [email protected]; [email protected]; [email protected]; [email protected])

The Central Graben of the North Sea is the region of greatest fault- related subsidence in this sedimentary basin. PreCretaceous rocks in the Graben below 3000m depth are characterised by high overpressure; the deep basin can be divided into a network of pressure cells in which the overpressure is retained beneath an aquitard/aquiclude of Cretaceous chalks and shales. Regional potentiometric mapping of the Graben delineates sharp energy gradients, and in conjunction with the rock geometry, allow5 the identification of potential flow paths between the pressure cells.

Computer simulation of regional overpressure evolution is used to investigate the controls on the pressure distribution. We note that the presence of a hydropressured zone at 3000m effectively decouples the post-crekeous section from the pre-Cretamus section: this is a major control on the magnitude and timing of overpressure. Modelling the interplay between pressure. aquitard permeability, structural position, and burial history allows us to identify zones of "anomalous" overpressure where high pressures are encountered at shallow depths. These zones of anomalous pressure are located on intrabasinal structural highs where low-permeability sealing rocks are thin.

Integration of the model with potentiometric maps allows us to recognise that pressuredriven flow from the deep overpressured graben is maintaining the elevated pressure over these structural highs. The intrabasinal highs are, in fact, leak points: zones of vertical fluid transfer through the aquitard. Major temperature anomalies are produced by thii vertical flow. The pattern of overpressure-caused fluid flow exerts a strong control on presentday pressures and has a major impact on the three-dimensional evolution of the hydrogeological systems in the Central Graben.

Core- to Basin-Scale Parameterization: Bridging the Gap Through Electrofacies Classification

Gerilvnn R M o h (Environmental Sciences Division, Oak Ridge National Laboratory*, Oak Ridge, TN 37831-6036; 6 15-576-3489)

The St. Peter Sandstone in the Michigan basin has undergone extensive diagenetic alteration due to pressure solution processes, resulting in

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banded cementation and stylolitization. lndividual horizontal hands range in size from millimeters to meters in thickness and occur in zones that are tens of meters thick. This geometry allows horizontal flow through higher permeability bands while creating significant impedance to vertical flow. Therefore, any meaningful analysis of flow characteristics within this formation must take these features into account.

Multivariate statistical and geostatistical techniques have been used to bridge the gap between observations at the core scale and parameter estimates at the basin scale. Central to these techniques is the identification of electrofacies which tie the borehole geophysical log responses to the porosity, permeability, and lithologic and diagenetic characteristics measured or observed at the core scale. Estimation of electrofacies Occurrence within the St. Peter Sandstone over a large portion of the Michigan basin indicates that zones of diagenetic banding extend laterally over at least tens of kilometers. Thus, while these pressure solution processes are local scale phenomena, their influence is felt at the regional scale. Correlation between banded zones and sequence stratigraphy indicate that the depositional environment has exerted some control over subsequent diagenesis. The presence of diagenetic banding can, in part, explain present day pressure transients observed within the St. Peter Sandstone.

* Managed by Martin Marietta Energy Systems, Inc., under contract DE-AC05-840R21400 with the U.S. Department of Energy.

Multi-scale parameterization of a hillslope hydrology model for soil water content and flux estimates on climate time-scales

- J Yeaklev (Coweeta LTER, Department of Biology, Virginia Tech, Blacksburg, VA 24061; 703/231-5965; [email protected]

G M Hornberger (Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22903; 804/924-7761)

J L Meyer (Institute of Ecology, University of Georgia, Athens, GA 30602; 706/542-3363

W T Swank (Coweeta Hydrologic Laboratory, U . S . Forest Service, Otto, NC 28763; 7041524-2128)

A terrain-based hillslope hydrology model was implemented to simulate soil water content and flux for two forested watersheds at the Coweeta Hydrologic Laboratory in the southern Appalachians. The model consists of three modules: (1) terrain fitting using TAPES-C; (2) dynamic canopy interception; (3) hillslope and channel dynamics using IHDM4 .

calibration was conducted at two scales: plot-scale measurements of soil moisture; watershed-scale measurements of streamflow. The calibration procedure was iterative between scales and was conducted across a range of antecedent conditions and storm types. period of recharge after severe drought showed that stormflow timing was poorly predicted, although overall streamflow volume was adequately estimated. Plot-scale simulations of soil moisture gradients compared well with measured gradients over the period of recharge.

Validation of the model over a

The Role of Groundwater Models in Locating a Safe Site for Britain's First Radioactive Waste Repository

C McKeown, R S Haszeldine and G D Couples (Geology Department, Universityof Glasgow, Glasgow. Scotland, UK, G12 8QQ; 041-339-8855; email: [email protected]; [email protected]; [email protected])

It is proposed that Sellafield in England is to be the site for Britain's first underground repository for low and intermediate-level radioactive waste. The site is within the Borrowdale Volcanic Group (BVG): 6000m of folded and metamorphosed Ordovician andesites and tuffs. These are unconformably onlapped by 4OOm of Carboniferous limestones, Permian clastics and evaporites, and more than 15OOm of Triassic sandstones. The company responsible for building and maintaining the repository, UK Nirex Ltd., indicate that groundwater velocities through the proposed repository location are negligible. We maintain that their simplistic numerical modelling did not adequately address the true geological setting and that the overall geometry of the rock units and groundwater salinities are major controls on the paths and rates of fluid flow. Our numerical modelling, performed using OILGEN (a 2-D finite dement code with coupled thermal and hydraulic processes) indicates that the repository will be subject to major fluxes of topographicallydriven water. Our results predict flows through the suggested site at rates of 1.1 to 19 ma-1 with return flow to the ground surface within 10, OOO years in certain cases. We find that flow through the repository is directly controlled by the permeability of the BVG and that the incorporation of lateral changes in salinity is essentiat to obtain a realistic model. If the engineered containment system fails, then chemical processes in the BVG fractures may be. the only remaining barrier to radionuclide contamination of the biosphere. Our study has shown that the hydrogeological all-round suitability of this site is questionable.

The Effect of Geologic Complexity on Groundwater-flow, a Case Study of a Glacial Esker Deposit

L A Scott and K Belitz (Both at Earth Sciences Depamnent, Dartmouth College, Hanover, NH 03755; 603-646-2373; e-mail: [email protected], [email protected])

Fine-scale numerical modeling was used to examine the influence of complex bedding relationships on the effective permeability of a glacial esker deposit. An esker deposit was mapped, at approximately 20:1, from a series of photographs of an outcrop in a quarry in Nonvich, VT. The area mapped is approximately 18 by 4 meters, with 83.5% bedded facies, and 16.5% massive facies. The map was divided into 316 hydrudic units, which are characterized by parallel, uN-directional bedding. A finiteelement mesh generator was used to divide the 316 hydrdic units into 3561 finite elements. Finite- element simulation was then used to conduct a series of numerical experiments to compute the effective permeability of the esker, as a function of two parameters: percentage of coarse, as opposed to fine, material and the permeability conuast between the two materials. Effective permeabdity was calculated by dividing the specific discharge by the head gradient. As expected, the effective permeability increases with increasing percentage of coarse material. Also, as the ratio of fme to coarse material permeability decreases, the effective permeability decreases. Results show that neither the arithmetic nor the p m & c means are acclrrate approximations of the effective penneabiiity values. From the results, a correlation between bedding-angle trends and effective permeability of the deposit can be inferred, and used to predict groundwater behavior in other deposits.

Hydrostratigraphy and Paleotopography of Carboniferous Ireland Framework for Hydrologic Modeling of the Carboniferous Carbonate- Hosted Zn-pb Deposifs of Ireland

M 1 Brown, K Belitz and N Oreskes (Department of Earth Sciences, Dartmouth College, Hanover, NH 03755-0371; 603-646-2373; e-maik [email protected]; [email protected]; [email protected])

The Carboniferous carbonate-hosted Zn-Pb deposits of Ireland provide a unique system in which to study the hydrological and thermal dynamics of sediment-hosted ore genesis. Located along fault-controlled margins of

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Early Carboniferous intracontinental basins, these deposits have been studied in detail both geologically and geochemically; yet, to date, a consensus as to their genesis remains elusive. One reason for this is the lack of physical data concerning potential flowpaths of mineralizing fluids during the Irish Carboniferous. Thus, while numerous theories of ore genesis have been proposed, including seawater convection, basin compaction/expulsion, and regional fluid flow, the models remain conjectural.

Three-dimensional pleogeographic and paleogeologic reconstructions corresponding to two of the mechanisms for ore genesis are here prrsented: (1) a submarine (Courceyan-Arundian) paleoenvironment for syngenetic, or "sedimentary-exhalative" theories of ore genesis, and (2) a subaerial (post-Arundian) paleoenvironment for theories of epigenetic mineralization, perhaps associated with regional-fluid flow during Early-Mid Carboniferous tectonism. These reconstructions identify regional boundary conditions (including land surface altitude, sea depth, and heat flow) and transport properties (including hydrostratigraphy and regional faults). Numerical values for these parameters are constrained by published Irish geological data and by data from modem environments analagous to Carboniferous Ireland. The resulting physical framework of Irish geology will be the basis for quantitative modeling of coupled heat and fluid-flow. The goal of this modeling study is to evaluate the potentia1 fluid-flow pathways and driving forces for mineralizing fluids in Carboniferous Ireland.

Major ion chemistly was determined for wekly stream samples colloweecled in 1993 fium snowmelt onset through early fall. Cation concentrations followed similar seasonal eends for all mateak& wirh peak mcentmtions occurring at snowmeli o m and lowest collcentratiotls during mid-summ. Calcium concentrations in the nested w a l e ranged from 150 to 200 lregn at smwmelt onset to 50 to 60 peqrl during sum me^ flow. Concentrations at BTA (largest wtershed) IMIP: alwajs high& While seasonal cation conCentratiom ~aried 2- to 3-foki, seasonal discharge ~aried hw orden of magnitude in the nested watershed% These stream\haters exhikit rapid flow response to dilute snowmelt input but are less respondve chemicatly. This dif€erence in resp3me suggeas that a substantial amwnt of dilute m m e l t is ro~led Uuough subsurtxe flow paths to read nith soil materials or displace more concentrated soil waters. U~theneded~atersheds,BouMaBdcationconcentrationSvariedont).

throughout the y w , which sugges(sthat a large reservoir ofwell mixed soil or grounawatersignificantlydampenssnowmeltinput~~forBoulderBtuok compared to the nested watedds. F'diminar). investigations show enough isotopic (% and D) di&rences among end- to facilitate flompath separation.

20% (01cium70 to 85 peqlx and discharge Mried onty one order of magnmde

digital.library.unt.edu/67531/metadc705890/m2/1/high_re… · 0 were originally inaugurated in 1976...

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