reservoir characterization research laboratory
TRANSCRIPT
Reservoir Characterization Research Laboratory
for Carbonate Studies
Research Plans for 2007
Outcrop and Subsurface Characterization of Carbonate
Reservoirs for Improved Recovery
of Remaining Hydrocarbons
Charles Kerans, F. Jerry Lucia, and James W. Jennings, Jr.
Co-Principal Investigators
Bureau of Economic Geology—Scott W. Tinker, Director
John A. and Katherine G. Jackson School of Geosciences
The University of Texas at Austin
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Research Plans for 2007
Reservoir Characterization Research Laboratory
Outcrop and Subsurface
Characterization of Carbonate Reservoirs for
Improved Recovery of Remaining Hydrocarbons
EXECUTIVE SUMMARY
The Reservoir Characterization Research Laboratory (RCRL) for carbonate studies is an
industrial research consortium run by the Bureau of Economic Geology (BEG) and the
Department of Geological Sciences of the John A. and Katherine G. Jackson School of
Geosciences, The University of Texas at Austin (UT). The RCRL’s mission is to use outcrop and
subsurface geologic and petrophysical data from carbonate reservoir strata as the basis for
developing new and integrated methodologies to better understand and describe the 3-D reservoir
environment.
Funding
With this proposal, we invite you to participate in continuing the RCRL Carbonate Reservoirs
Research Program. A list of 2006 sponsors can be found at the end of this proposal. In 2007 the
annual RCRL Industrial Associates contribution to the program will remain $45,000 per year.
RCRL Program
The RCRL program, running continuously since 1987, has produced more than 45 external
publications, as well as BEG publications, on carbonate reservoir characterization, sequence
stratigraphy, petrophysics, geostatistics, and petroleum engineering. RCRL has maintained a
membership of between 13 and 18 companies per year. The sponsorship currently has strong
interests in a variety of domestic and international carbonate reservoirs ranging in age from
Ordovician to Tertiary. This enrollment, supplemented by other grants, supports between three
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and six professional staff members and varying numbers of graduate student research assistants,
as well as strong computer, editing, and graphics services. All staff members have extensive
industry experience or have worked closely with industry and are well aware of the challenges
and questions facing development geoscientists and engineers.
Principal Staff
Dr. Charles Kerans, Geology Professor, Principal Investigator
Mr. F. Jerry Lucia, Geological Engineer, Principal Investigator
Dr. James W. Jennings, Jr., Reservoir Engineer, Principal Investigator
Dr. Xavier Janson, Geologist
Mr. Jerome A. Bellian, Geologist
Dr. Daniel Kurtzman, Hydrologist
Associate Staff
Dr. Fred Wang, Reservoir Engineer
Dr. Hongliu Zeng, Geophysicist
Graduate Students in RCRL Research
Graduate student research, a growing element of the RCRL program, allows us as a group to take
on many more projects and visit more field areas than previously possible. This year was the first
year that students headed up the review meeting. On the basis of sponsor input we will continue
to develop the student research component of the program. Currently we have nine graduate
students involved in the RCRL—Enzo Achoncha, Jerome Bellian, Jason Clayton, Ned Frost,
Beatrix Garcia-Fresca, Ryan Phelps, Ted Playton, Sam Scott, and Adolphus Wilson.
If you have any questions on any aspects of the RCRL Carbonate Reservoirs Research Program,
please contact Charlie Kerans (512-471-4282 or [email protected]), Jerry Lucia (512-
471-7367 or [email protected]), or Jim Jennings (512-471-4364 or
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RESEARCH DIRECTIONS FOR 2007
Areas of Research
Each year we combine industry input with our own ongoing research plans to develop a set of
key geological and engineering research topics. Plans for 2007 are focused on the following
areas:
Areas of Research
(1) Geologic Characterization and Fluid Flow in Nonmatrix Pore Systems
(2) Outcrop Studies of Carbonate Heterogeneity Style—Platform, Slope, and Basin
(3) Subsurface Reservoir Models and Modeling Methods
(4) Predictive Dolostone and Limestone Diagenetic Studies
(5) Database
Information Transfer
General
Our industry sponsors will continue to receive research results at annual review meetings, in
short courses and workshops, during mentoring activities, in publications and CD’s, and on our
developing members-only RCRL database (http://begdb1.beg.utexas.edu/rcrl/login.aspx).
Workshops
Many of our sponsoring companies have requested field trips and workshops that present past
research results in contrast to the annual review and field trip that presents current results. This
request occurs because the flow of new geoscientists to sponsor companies creates a need for
training in classical field areas and from short courses that summarize key findings of the
consortium. To meet this need we plan to provide a carbonate field trip and reservoir modeling
workshop annually to educate those geoscientists who are not fully aware of our technical
advances. In 2006 we conducted one reservoir modeling workshop, and we plan to continue this
practice by presenting a second modeling workshop in May 2007. In addition, we plan to lead a
general field trip in April 2007 for our sponsoring companies.
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Mentoring program
Direct contact with the technical staff of our sponsoring companies is an important ongoing
aspect of our information transfer program. This interaction allows us to test our concepts and
methods on real problems, while providing an opportunity for our sponsors to learn how to apply
our methods in developing new reserves. Sponsors are encouraged to contact us with projects
that could be mutually beneficial.
RESEARCH PROGRAM FOR 2007
Geologic Characterization and Fluid Flow in Nonmatrix Pore Systems
Permeability modeling is a fundamental problem in reservoir characterization. The RCRL has
developed advanced methods of modeling matrix permeability suitable for filling geologic
models with petrophysical properties. Modeling of nonmatrix flow, flow in touching-vug pore
systems that include fractures, solution-enlarged fractures, large vugs and caverns, and collapse
breccias remains a major problem in carbonate reservoir characterization. For the past several
years the RCRL has embarked on research to investigate the nature and fluid-flow characteristics
of nonmatrix flow by (1) collecting and analyzing large outcrop samples using high-resolution
CT scans, (2) mapping touching vugs and matrix porosity in outcrops of karsted carbonate, (3)
describing a karsted dolostone reservoir (the San Andres Hobbs Unit), and (4) investigating
seismic methods for imaging vuggy pore space, including karst features and moldic grainstones.
In 2007 we will continue to research this problem focusing on the following projects.
Pipe Creek Outcrop Study
In previous years we studied fluid flow in a vuggy rudist rudstone sample collected from the
Cretaceous Pipe Creek Reef. High-resolution CT scans and laboratory fluid-flow experiments
were conducted with this sample to determine vug-size statistics, vug-connection geometry,
permeability, and tracer transport properties. In 2005 we initiated a larger scale study at the Pipe
Creek outcrop using two 25-ft wells drilled 5 ft apart. A preliminary air extraction test with these
wells indicates connected vugs at the 5-ft scale and an effective permeability of 1 Darcy,
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consistent with whole-core analysis of four core samples from these two wells. We plan
additional well tests in 2007 to refine our permeability estimates, and tracer tests to determine the
amount of pore space contributing to fluid flow.
Lake Medina Outcrop Study
In 2007 we plan to continue our study of the Lake Medina outcrop using coupled matrix-fracture
fluid-flow modeling in 3D and outcrop characterization of vugs. The outcrop includes vugs that
are preferentially located at the intersections of fractures and grainstone layers. We thus
hypothesize that the flow rate of groundwater and the rate of dissolution were greatest at these
intersections. To test this hypothesis we are constructing 3D fluid-flow models, with fracture
porosity and permeability superimposed on a stratigraphic grid of matrix petrophysical
properties. Preliminary results indicate that flow-rate maxima do occur at intersections of
permeable fractures and grainstone layers, suggesting that the simulated flow-rate field can be a
tool for predicting the location of vugs. We plan to study the spatial arrangement and strength of
the simulated flow maxima resulting from various combinations of boundary conditions, fracture
permeabilities, and matrix heterogeneities.
Additional plans for the Lake Medina outcrop study include (1) development of
quantitative field methods for surveying vug size, location, density, and connectivity, using both
traditional measurements and lidar data; (2) synthesis of the flow-model results and field data to
improve modeling of discrete fractures and vugs; and (3) development of scaleup methods to
estimate effective flow properties in subsurface models having similar combinations of matrix,
fracture, and vug permeability.
Regional Study of a Cretaceous Karst Reservoir
An extensive karst system is located in Cretaceous carbonates of Central Texas and houses the
world-class Edwards aquifer. This aquifer and karst system have been studied extensively but
only on a regional scale. We have focused on the 100-ft scale with our study of the Medina
roadcut, and have reported results in the past several annual review meetings. In 2007 we
propose to extend our study to include other outcrops and roadcuts, as well as numerous quarries
and caverns. We intend to use these data to quantify various genetic geometries, scales of
touching-vug interconnections, and links between vug development and stratigraphy.
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Franklin Mountain Karst Study
Our ability to develop robust geologic models of touching-vug systems and to generate efficient
and reliable performance predictions for these rocks remains inadequate. Mapping of breccia
bodies over several-square-kilometer areas, such as those exposed in the southern Franklin
Mountains in El Paso, Texas, is one way to begin to assess lateral and vertical heterogeneity at
reservoir scales.
Field mapping of the uppermost El Paso Group (Lower Ordovician), just below the
regional Sauk unconformity (30-m.y. time gap) has been conducted and will be incorporated into
the recently acquired airborne lidar data set. High-resolution ground-lidar data will continue to
be added to the airborne data in order for us to construct high-resolution (3- to 5-cm point
spacing), detailed karst-body boundaries in 3D. The objective of this work is to better delineate
breccia bodies and reconstruct the events that led up to the emplacement of large laterally and
vertically extensive breccia bodies, as related to long-term unconformity and exposure events.
Hobbs San Andres Karst Reservoir Study
The RCRL approach to understanding carbonate reservoirs is to study outcrop analogs of
subsurface reservoirs. For the past few years we have been investigating the stratigraphy,
petrophysics, and production characteristics of the Hobbs San Andres reservoir in the Permian
Basin, Texas and New Mexico, supported by Oxy Permian. We have reported on our research
results at the annual review meetings and plan to continue this investigation toward construction
of a realistic simulation model. To that end we plan to further investigate the distribution of
nonmatrix flow by studying production characteristics and injection profiles in the lower part of
the reservoir, where injection is taking place.
Hobbs San Andres Karst Reservoir Model
A sequence-stratigraphic model and a rock-fabric petrophysical study of the Hobbs San Andres
reservoir were both completed in 2006. The petrophysical study confirmed the presence of large
permeabilities dominated by touching-vug flow in some parts of the reservoir, and highlighted
the importance of injection-profile data in mapping these karst-influenced regions. In 2007 we
plan to build a gridded porosity and permeability model of the reservoir to test our ideas on
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model construction in touching-vug settings like Hobbs. The model will combine porosity and
matrix permeability modeled in the stratigraphic framework according to our usual rock-fabric
and geostatistical methods, with maps of karst-related permeability enhancement generated from
injection-profile data.
Seismic Modeling of Separate-Vug Pore Space
We will continue to develop seismic processing and interpretation strategies to identify and map
moldic porosity from 3D seismic data. In 2005 we studied seismic response to vuggy porosity in
high-frequency cycle 7 of the Lawyer Canyon outcrop. The study showed that the difference in
acoustic properties between separate-vug grainstone and nonvuggy grainstone can generate a
large enough impedance contrast to be detected on poststack seismic images. Initial results from
modeling amplitude variation with offset (AVO) of the cycle 7 grainstone showed that the
difference in acoustic properties might be detected and mapped using AVO techniques. In 2007
we are planning to collect a significant number of plug samples within the grainstone body of
cycle 7 to characterize differences in petrophysical and acoustic properties of the two different
pore types present in these grainstones. We will then measure elastic properties of these rock
samples in the laboratory (in collaboration with either Jon Holder from the Department of
Petroleum Engineering Sciences at UT or the Petrophysical Laboratory of University of Miami).
In collaboration with Diana Sava (BEG), we will investigate the robustness of a current rock
physics model for explaining the elastic properties of these rocks. On the basis of both a robust
rock physics model and laboratory measurement, we will then expand our previous AVO study.
The goal is to evaluate the feasibility of developing a prestack seismic detection and
characterization workflow for separate vugs. Once the workflow is validated on synthetic data,
we will ultimately try to apply it to a subsurface data set. For that purpose, we would like to ask
help from our sponsors to locate and obtain a subsurface data set that contains reservoir rocks
with both interparticle and separate-vug porosity.
In conjunction with the flow-modeling study of Lawyer Canyon, we will begin to
investigate the sensitivity of 4D seismic in such a system by calculating at various times a series
of 3D synthetic seismograms from the fluid-flow model prediction. Doing so, however, will
require that we have a robust rock physics model that can describe, under various degrees of
fluid saturation, the elastic behavior of various rocks present in the model.
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Outcrop Studies of Carbonate Heterogeneity Styles—Platform, Slope, and Basin
Two main areas of outcrop research are targeted for continued development of our understanding
of carbonate slope and slope-to-basin transitions. The Shumard Canyon area and a new area in
the Albian of the Fort Stockton Basin will be the focus of slope research. Shelf cycles in
carbonates dominate production from carbonate reservoirs and have been at the center of RCRL
research since its inception. We are considering two new areas, the Permian Khuff platform-top
cycles exposed in Jebel Aktar in Oman and the Cretaceous-Tertiary carbonates of Libya. Both
areas have exceptional outcrop of transitional to greenhouse carbonate-shelf cycles and are of
keen interest as outcrop analogs to producing horizons in these regions.
Shumard Canyon and the Platform Margins of the Guadalupe Mountains
Carbonate-platform margins are one of the more complex reservoir settings in terms of primary
porosity distribution and flow-unit structure. Carbonate-ramp systems are relatively systematic
and have been extensively studied. Similarly, reef-rimmed margins, although not totally
understood in terms of processes and architecture, have been examined in detail. A wide
spectrum of carbonate margins exist between the ramp and rimmed-shelf end members, and
although they contain significant hydrocarbon accumulations, they have received less intense
study.
The Victorio Peak to Bone Spring transition along the Western Escarpment is an
impressive 500-m-thick exposure of a shelf-to-basin transition in a moderately steep profile that
cannot easily be characterized as a ramp (depositional dips are between 10° and 25°) or a
rimmed shelf (no well-defined margin facies tract or debris-flow upper slope). The focus of
research here is to evaluate the nature of the shelf-to-basin transition, to map the distribution of
grain-rich reservoir facies, and to understand the relative role of traction deposition, sediment
gravity flows, and mass-transport processes and slumps in prograding carbonate margins.
Reconnaissance mapping and section measuring, coupled with lidar imaging, was begun in 2006
and will serve as the basis for an expanded effort in 2007, with continued mapping and modeling
downslope into the Williams Gulch and Bone Canyon areas.
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Airborne Lidar Model of the Southern Guadalupe Mountains
At what scale do large platform-margin collapse scars or reentrants influence slope and basin
accumulation of reservoir-quality carbonate fan-channel complexes? What large-scale structures
control the character of platform-margin and slope accumulations, their fracture patterns, and
their compaction-driven geometries? We believe that a 3D analysis of the Capitan shelf-to-slope
system as exposed in the Guadalupe Mountain National Park is ideal for addressing issues
related to large-scale stratal architectures of carbonate platforms.
An airborne lidar survey will be carried out with a helicopter-mounted unit shooting at a
low or oblique angle, allowing effective capture of cliff faces and flatter surfaces. This method
was used successfully to collect lidar data from the Franklin Mountains in the fall of 2006.
Airborne data collected in this way from the Guadalupe Mountains will allow us to work in
digital 3D structure and stratigraphy at the platform scale, rather than at the flow-unit to local
platform-margin scale associated with most of our models constructed using ground-based lidar.
We will take bids over a range of coverage areas of varying size during the winter and will
evaluate feasibility on the basis of cost and data density. Funding will come from Kerans’ start-
up funds, RCRL, and possible additional company input.
I-10 Ft. Stockton Embayment Ramp to Basin Profile
The RCRL is currently working on a variety of slope-to-basin deposits associated with different
platform morphologies, such as steep margins of the Capitan (Playton) and moderate slopes of
the prograding shelf of Last Chance Canyon (Ryan Phelps and Sam Scott), Victorio Peak, and
Bone Spring Formation in Victorio and Shumard Canyons.
In 2007 we would like to start investigating a low-angle slope-to-basin profile formed
along the eastern flank of the Fort Stockton embayment. The uppermost Albian (Cretaceous)
succession outcropping along the I-10 corridor from Ozona to Bakersfield (Texas) shows an
almost continuous section from the ramp crest to the intrashelf basin with an undisturbed,
exhumed Cretaceous paleobathymetry. We plan to capture data on the shape of the profile using
available DEM data that, although low resolution, should be sufficient to capture the low-
gradient slope involved. We will then visit representative roadcuts and outcrops along the
profile, from the shelf to the basin, collecting samples to investigate not only the facies
architecture but also the diagenetic changes observed along the profile. One of the unique aspects
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of this profile is the superb exposures of the rudist rim and basinal equivalents, which contain
both mud-rich and grain-rich reservoir-quality facies.
Subsurface Reservoir Models and Modeling Methods
In past years the RCRL has developed a systematic method for integrating high-resolution
sequence stratigraphy, rock fabrics, core data, well log data, geostatistics, and scaleup
approximations to produce superior 3D models of petrophysical stratification common in
shallow-water platform carbonate reservoirs. These methods were demonstrated in the
construction of a model for a one-square-mile area of the South Wasson Clear Fork reservoir in
West Texas. We believe that these model construction methods can be adapted to improve 3D
petrophysical modeling of any stratified carbonate system, and we are actively seeking
opportunities to test the methods in other reservoirs, particularly Cretaceous examples. Because
of the small size of the South Wasson Clear Fork model, only moderate lateral petrophysical
trends were encountered. Therefore, in 2007 we plan to test our petrophysical model construction
methods in a larger reservoir having more significant lateral petrophysical trends and to include
seismic methods for filling the interwell volume.
Fullerton Clear Fork Reservoir Model
We have selected the Fullerton Clear Fork reservoir in West Texas because of its size (55 square
miles), existing high-resolution sequence stratigraphic and petrophysical framework, and
existing database of core data (25 wells) and quality-controlled well logs (850 wells). The BEG
has recently completed a detailed geological and petrophysical model of this reservoir. Our
approach will be to test our more advanced methods of distributing properties within the existing
stratigraphic framework by using petrophysical properties calculated from wireline logs
employing the rock-fabric method.
Lawyer Canyon Outcrop Fluid-Flow Model
The Lawyer Canyon San Andres outcrop on the Algerita Escarpment in the Guadalupe
Mountains of southeastern New Mexico is a classic field site for sequence stratigraphy, spatial
variability, and fluid-flow effects of petrophysical properties in a Permian dolomitized carbonate
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ramp. Some the earliest RCRL work on sequence stratigraphy and rock-fabric methods were
conducted on that outcrop. Many of our fundamental insights of the analysis and modeling of
spatial variability were derived from petrophysical data collected there. Some of our most
fundamental conclusions on fluid flow and scaleup were developed from 2D models of the
outcrop. More recently lidar data from the Lawyer Canyon outcrop were used to construct a 3D
geological model. In 2007, to complete our documentation of this classic outcrop, we plan to
further develop this 3D model into a gridded porosity and permeability model for 3D fluid-flow
simulation.
Capillary Pressure Modeling of Initial Water Saturation
To estimate the volume of remaining oil as a target for advanced recovery methods, the original
volume of oil and gas in a reservoir is commonly compared with the produced oil and gas.
Wireline logs are the principle source of saturation data used to make this estimate. In reservoirs
where wireline logs are inadequate, however, mercury capillary pressure saturation models are
commonly invoked to model initial water and hydrocarbon saturations. The common method is
to normalize capillary pressure data using permeability-porosity ratios. The RCRL method is to
normalize capillary pressure data on rock fabrics. In the past we have generated rock-fabric-
specific models for initial water saturation on the basis of porosity and capillary pressure
(reservoir height) but have been unable to produce a general equation that relates initial
saturation to reservoir height, porosity, and rock-fabric number. However, we now have new
capillary pressure data and thin-section descriptions, and in 2007 we plan to develop a general
rock-fabric capillary pressure model using this augmented data set.
Predictive Dolostone and Limestone Diagenetic Studies
Predicting diagenesis is a complicated task that involves (1) identifying the diagenetic process,
(2) modeling the hydrology and chemistry of the diagenetic fluid, and (3) relating the diagenetic
product to the physical and chemical character of the original sediment and depositional
environment. Historically the RCRL has not focused on diagenetic studies. In the past several
years, however, we have supported student theses investigating dolomitization processes. In
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2007 we plan to continue student support in this area and to initiate an investigation into burial
diagenesis of limestones.
Predictive Diagenetic Modeling of the Dolomitization Process
For the past several years the RCRL has supported student research on modeling dolomitization
by hypersaline reflux. Initial research focused on modeling dolomitization of a single high-
frequency cycle. Current research focuses on modeling dolomitization of the extensive San
Andres (Permian) outcrop located on the Algerita Escarpment, Guadalupe Mountains, New
Mexico. The outcrop, 1,500 ft high and more than 30 miles long, has an equivalent subsurface
section some 50 miles downdip and along depositional strike. Initial results were presented at the
last annual meeting and include limestone-dolostone mapping, enlarging the stratigraphic model,
and construction of the subsurface cross section showing distribution of anhydrite beds in the
upper part of the formation. In 2007 we plan to focus on modeling the paleohydrology using
hypersaline reflux dolomitization concepts.
Burial Dissolution of Limestone for Creating and Modifying Carbonate Pore Space
The loss of porosity during burial of limestone sediments is a well-known fact. Pore space is
modified during this process, with pore space being both destroyed by compaction and
cementation and created by mineralogical stabilization and grain crushing. The overall trend,
however, is for porosity to be reduced with burial. Some geologists have concluded that porosity
can be increased at depth by hydrothermal dissolution. In 2007 we plan to investigate the
evidence for porosity increases related to burial diagenesis of limestones and to initiate a study of
a limestone reservoir where porosity is thought to have been increased rather than lost due to
burial processes.
Database
For 17 years the RCRL has been describing, interpreting, and modeling carbonate strata and
petrophysical properties at the reservoir scale and, to a lesser extent, at the exploration scale.
During this time, a range of data have been collected, including outcrop measured sections, core
descriptions, petrophysical data, and complex 3D geological, petrophysical, and simulation
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models. We have begun compiling and making available some of this data in the form of
databases populated with tables and images. All data are referenced to a geographic area,
geologic time, and, where applicable, latitude and longitude location. A visual search engine is
also under development through a collaboration between Statoil and the RCRL to make data
extraction from the database as easy as possible. Subscribing companies can access the database
using Internet Explorer. Each company has a unique user account and password to insure access
only to sponsors.
Population of the database will continue in 2007. Data types currently loaded on the
website include lidar models, Gocad models, LAS log and measured-section files, core
descriptions, facies photos and photomicrographs, porosity and permeability data, stratigraphic
sections, and maps. Data we intend to add this year include posters and presentations from
research staff and students, field-trip guidebooks, and additional digital field studies.
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List of 2006 Sponsors
Anadarko
Aramco
BP
Chevron
ConocoPhillips
ENI
ExxonMobil
Great Western Drilling
Kinder Morgan
Marathon
Norsk Hydro
Oxy Permian
PDO
Pioneer
Shell
Statoil