Despite more than 60 years of production history, recovery of the more than 1.5 billion barrelsof oil in the Fullerton Clear Fork field, a shallow-water platform carbonate reservoir of EarlyPermian age in the Permian Basin of West Texas, remains a challenge. To develop a betterunderstanding of the distribution of the original hydrocarbon resource and to devise strategiesto recover the huge volume that still remains, we undertook a comprehensive, multidisciplinarystudy of the reservoir. Crucial elements of the study include (1) geological models of analogousoutcrops, (2) description of more than 14,000 ft of core, (3) new core data for rock-fabricanalysis, (4) analysis and correlation of more than 850 wireline log suites, (5) a 3-D seismicinversion porosity model, (6) a 35,000-acre (14,000-hectare) reservoir model, and (7) a 2,000-acre (800- hectare) flow simulation.

The study utilizes robust outcrop models as a key to proper interpretation of geological,petrophysical, and geophysical subsurface data sets. It demonstrates procedures for producingand utilizing a geologically constrained reservoir framework in reservoir modeling andsimulation. It shows the tremendous potential of iterative 3-D seismic porosity inversionmodels in defining porosity distribution. It illustrates the importance of a rock-fabric-basedapproach for defining porosity/permeability relationships. Finally, the study defines thedistribution of original and remaining oil volumes and provides insights into how theseresources may best be recovered.

INTRODUCTION

Cyclicity and Reservoir FrameworkCores and outcrops demonstrate a direct relationship between facies, cyclestacking, and porosity: high porosity is usually associated with grain-richfacies at cycle tops. This relationship forms a basis for the use of porositylogs in cycle correlation and flow-unit definition.

L 2.3 is a low-accommodation sequence in which cycles are characterizedby porous tidal-flat caps that are readily defineable and correlatable onporosity logs.

L2.2 and L2.1 comprise dominantly subtidal cycles whose tops are generallygrain-rich packstones. Note good correlation between high porosity andcycle tops and poor correlation to gamma-ray logs.

6700'

6750'

6800'

6700

6800

CGR

Low

er C

lear

For

k

L 2.3

SGR

L 2.2

GR

Neutron

Core

Density

Porosity (%)30 0

Peloid packstone

Peloid wackestone-packstoneSkeletal wackestone

Peritidal mudstone Ooid/peloid grain-dominatedpackstoneSiltstone/sandstone

Tidal flat

Tidal-flat-capped cycle

Lower Clear Fork L 2.3

CGR

Low

er C

lear

For

k

L 2.2

SGR

L 2.1

GR

Neutron

Core

Density

Porosity (%)30 0

L 2.2L 2.3

6850'

680

685

Peloid packstone

Peloid wackestone-packstoneSkeletal wackestone

Peritidal mudstone Ooid/peloid grain-dominated packstoneFusulinid wackestone-packstone

Tidal flat

Tidal-flat-capped cycle

Lower Clear Fork L 2.2

6950

Core porosity

Neutron porosity

Peloidal packstonePeloidal wackestone

Tidal-flat wackestone-packstone

Fusulinid wackestone-packstoneOncoid-fusulinid wackestone-packstone

Peloidal grain-dominated packstone

Tidal-flat cycle topSubtidal cycle top

GRPorosity (%)30 0

7000

6950

7000

Lower Clear Fork L 2.1Depth

(ft)

Stephen C. Ruppel, Rebecca H. Jones, F. Jerry Lucia,Fred P. Wang, Hongliu Zeng, Jeffrey A. Kane,

and James W. Jennings, Jr. SETTING

CA B

A B

Mineralogy and Controls of Porosity Distribution

Field Structure and Data

Type Log Seismic Architecture

Middle ramp and ramp crest subtidal, grain-rich facies L2.1 & L2.2 (Lower Clear Fork)

Inner ramp tidal flat, mud-rich facies L1 & L2 (Wichita & Lower Clear Fork)

Karst facies: L1 & L2 (Wichita)

A. Moldic ramp crest limestone grainstoneB. Peloid grain-dominated dolomite grainstone (interparticle pores)C. Peloid packstone (moldic and interparticle pores)

Polymict and monomict conglomerate and breccia locallypresent above and below L1/L2 sequence boundary.

Distal outer ramp clinoforms L1 (Abo)

Fusulinid-crinoid wackestone-packstone with interparticle pores

Proximal outer rampL1 (Abo); L2 (Lower Clear Fork)

Fusulinid wackestone-packstonewith moldic and interparticle pores

Reservoir architecture defined by 3-D seismic and outcrop dataL1: progradational, partly clinoformal; L2: largely aggradational and horizontal

Abo

Wichita

LCF

Tubb

L1

L3

West East

UCF

L2.0L2.1L2.2L2.3

A. Fenestral mudstone-packstone (fenestral pores)B. Laminated mudstone (fine- to micro-crystalline pores)C. Clay-rich organic-pond mudstone

Although mostly dolostone, the reservoir contains significant volumes of limestone whosedistribution is important for (1) defining reservoir architecture, (2) controlling fluid flow, and(3) understanding porosity development.

Sequence Stratigraphic Framework

C

GEOLOGICAL CHARACTERIZATION

Field structure is a function of Pennsylvanian block faulting. Thereis good evidence of continuing reactivation of some of faults duringand after Leonardian deposition.

-

-

-

-

0 8000 ft

UnitBoundary

C.I. 40 ft

CoreImage log

Well

Deep fault

3-DSeismic

FlowSimulation

Study

3-DInversion

Study

A

A'

Inner ramp tidal-flat facies withlocal pond facies

Outer ramp clinoformal,fusulinid-crinoid packstone-wackestone

Middle ramp peloid faciesInner ramp tidal-flat faciesOuter ramp fusulinid facies

Inner ramp tidal-flat-cappedsubtidal facies

Inner ramp tidal-flat facies

Wichita FaciesLower Clear Fork Facies

Abo Facies

Systems Tracts

L1

Abo

HFSL2.1

Low

er C

lear

For

kTu

bbW

ichi

ta

HFSL2.2

HFSL2.3

L3

HFSL3.1

Abo

Low

er C

lear

For

kTu

bbW

ichi

ta

HFSL2.0

6400

6950

7000

7050

7100

7150

7200

7250

7300

7350

GR POROSITY (%)10030 20 10 0 -10

6900

7000

7100

7200

7300

7400

7500

7600

Permeability(md)0.01

CORE

6800

7700

7000

7100

7200

7300

7400

7500

7600

GR N D

Northwest SoutheastDIP SECTION

GR P N DGR P N D

6550

6600

6650

6700

6750

6800

6850

6900

6950

7000

7050

7100

7150

7200

7250

7300

73507360.0

6400

6450

6500

6550

6600

6650

6700

6750

6800

6850

6900

6950

7000

7050

7100

7150

7200

7250

7300

7350

7400

7450

7500

SGR P N D

SGR P N D

SGR P N D

A A'

01000

Datum: Base of Sequence L3

CGR SGR PE Neu Den

Low

er C

lear

For

kW

ichi

ta

Abo

Tubb

HFS L2.1

HFS L2.2

HFS L2.3

Sequence/Cycle Tops6500

-3500

-4000

Depth(ft)

7000

Prod

uctiv

e In

terv

al

HFS L2.0

Peritidal/tidal flat Subtidal

L 3

L 2

L 1

Bureau of Economic GeologyJackson School of Geosciences

The University of Texas at AustinAustin, TX 78713-8924

Geographic Distribution of LimestoneL2.1 Lower Clear Fork L2.0 WichitaL2.2 Lower Clear Fork

Limestone abundant Dolostone L1 Wichita/Abo margin

Multidisciplinary Reservoir Characterization of a Giant Permian Carbonate Platform Reservoir: Insights for Recovering Remaining Oil in a Mature U.S. BasinMultidisciplinary Reservoir Characterization of a Giant Permian Carbonate Platform Reservoir: Insights for Recovering Remaining Oil in a Mature U.S. BasinSETTING GEOLOGICAL CHARACTERIZATION

Stratigraphy

SE

RIE

S

STA

GE

NEW MEXICO TEXAS

LO

WE

R P

ER

MIA

N

Leo

nar

dia

n

SUBSURFACE

Cle

ar F

ork

Gro

up

UpperClear Fork

WichitaGroup

San Andres

Glorieta

Yes

o

Paddock

Blinebry

Abo

Drinkard

Tubb

PLATFORM MARGIN

VictorioPeak

Cutoff

BoneSpring

San Andres

Tubb

Glorieta

LowerClear Fork

San Andres Leo 7-8

Leo 6

Leo 2

Leo 1

Leo 3

Leo 4

Leo 5

Wolf 3Wolfcamp Hueco HuecoWolfcamp

VictorioPeak

Glorieta

Abo

OUTCROP

SEQUENCE

Guad 1

PLATFORM AND MARGIN GUADALUPE MOUNTAINS/SIERRA DIABLOTexas - New Mexico

Ku

ng

uri

an

STA

GE

Geography

Fullerton Clear Fork field is one of the largest fields in the Permian Basin, covering anarea of about 35,000 acres (14,000 hectares). The field, which includes more than 1,200wells, contained between 1.5 and 2.0 billion barrels of oil at discovery.

KETCHUM MT.

DOVE CREEK

PAROCHIAL-BADE

HOWARD-GLASSCOCK

VAREL

REVILOLUCY

DIAMOND -M-

SHARON RIDGE

COLEMAN RANCH, N.

COLEMANRANCH

WESTBROOK, EAST

MIRIAM

P.H.D.

ROCKER -A-

GUINN

POST

WTG

SMYER

ROPES, E.

HARRIS

ROBERTSON, N.

RUSSELL

WASSON 72

OWNBY

PRENTICE

KINGDOM

SUNDOWN LEEPER

WARHORSE

BROWNLOVINGTON

MIDWAYDOUBLE A, SOUTHDOUBLE A

EMPIRE

BUCKEYEVACUUMCORBIN

HAL JAMAR

LEVELLAND

ANTON

ANTON-IRISH

RIDGE

HOOPLE

EDMISSON

KEYSTONE

KEYSTONE, SOUTH

EMPORER

MONAHANS, N.

DOLLARHIDEJUSTIS

FOWLER

TEAGUE

DRINKARD

OIL CENTER

METZ

PENWELL

C-BARMONAHANS

CRAWAR

SAND HILLS

MCKEE

BAYVIEW

SUN VALLEY, N.BROOKLAW

SUN VALLEY

BROWN & THORP

WENTZTIPPETT

UNION

FULLERTON

SHAFTER LAKE

DEEP ROCK

FUHRMAN SOUTH

NIX, SOUTH

BLOCK 12

MARTIN

TXL

MONUMENT BLOCK A-34

HOBBS

WEIR

SCAGGSHOUSE

BRUMLEY

GOLDSMITH

GOLDSMITH, W.

TURNER-GREGORY

EMBAR

JACKSON

CROSBY

DICKENS

KENT

SCURRY

LYNN

DAWSONGAINES

MITCHELL

GLASSCOCK

ANDREWS

MIDLAND

TOM GREENSTERLING

UPTON

ECTOR

TERRY

BORDEN

GARZA

MARTIN

HALE

LUBBOCKHOCKLEY

LAMB

CHAVES

EDDY

LOVING

REAGAN

CRANE

PECOS

WINKLER

COCHRAN

YOAKUM

WARD

IRION

LEA

HOWARD

MIDLANDBASIN

BLINEBRY

NORTHERN

EASTERN

SHELF

SHELF

DELAWAREBASIN

Fullerton Field

New MexicoTexas

CENTRALBASIN

PLATFORM

0 25 50 milesLeonardian shallow water carbonate reservoirs

RILEY, NORTH

FLANAGAN

WELTMER

WARREN

PADDOCK

ROBERDEAU, S.

BROWN & THORP,EAST

N

Mineralogy and geochemical data suggest that high-porosity trend in Wichita is the resultof early dolomitization along the outer tidal-flat margin. High-porosity trend in the LowerClear Fork is the result of early calcite stabilization along the platform-margin ramp crest.(Isotope data from this study and Kaufman [1991]).

Early Diagenesis and Structure Control Porosity Distribution

Later reflux dolomitization Early calcitecementation

andstabilization

Later reflux dolomitizationEarly seawaterdolomitization

andstabilization

L1 - L2 Wichita Platform L2 Lower Clear Fork Platform

B

L1 platformmargin

Core

Image log

Unit boundary

Low-porosity Wichitainner ramp tidal flat

High-porosity Wichitatidal-flat margin

Low-porosity Lower Clear Forkouter ramp subtidal

2.8 0/00 d18O

3.0 0/00 d13C

0.1 0/00 d18O

2.5 0/00 d13C

-3.0 0/00 d18O

4.0 0/00 d13C

2.5 0/00 d18O

2.6 0/00 d13C

NN

0

0 4 mi

6 km

High-porosity LowerClear Fork ramp crestLow-porosity Lower Clear Forkmid-ramp subtidalWichita/Abo inner/outerramp margin

1. Tidal-flat (mud-rich) limestones (L1/L2 Wichita) are low-flow baffles, whereas subtidal(grain-rich) limestones (L2 Lower Clear Fork) are high-flow zones.

2. Reservoir architecture in the poorly cyclic peritidal L1/L2 Wichita succession is best definedby limestone distribution (cycle bases).

3. Limestone is most common in the transgressive leg of the L2 sequence. This is consistentwith incomplete reflux dolomitization from an updip/upsection fluid source.

Stratigraphic Distribution of Limestone

Wic

hita

Low

er C

lear

For

kA

boTu

bbGR N D

GR N D GR N D GR N D GR N D GR N D

HFSL 2.1

L 1

HFSL 2.2

HFSL 2.3

West East

L 3

6450

6500

6550

6600

6650

6700

6750

6800

6850

6900

6950

7000

7050

7100

7150

7200

7250

7300

7350

7400

HFSL 2.0

L 2

6400

6500

6600

6700

6750

6800

6900

7000

7100

7200

7300

7350

6500

6550

6600

6650

6700

6750

6800

6850

6900

6950

7000

7050

7100

7150

7200

7250

7300

7350

7400

6450

6500

6550

6600

6650

6700

6750

6800

6850

6900

6950

7000

7050

7100

7150

7200

7250

7300

7350

7400

6450

6500

6550

6600

6650

6700

6750

6800

6850

6900

6950

7000

7050

7100

7150

7200

7250

7300

7350

7400.0

DolostoneLimestone100 30

0

ft m

0

Depositional Model

Inner ramp Rampcrest

Outer ramp

Slope –basin

Peloidwackestone-packstone Peloid/ooid

grain-dominatedpkstn-grnstn

Crinoid-brachiopodwackestone-packstone

Starve

d bas

in

Sabkha, tidal fla

t

Highly variableexposure-related facies

Buildupsand flanking

crinoid packstone

Middle ramp

Fusulinidwackestone-packstone

QAb3741c

Lagoon,

protected flat

Clinofo

rm sl

ope

(0.5-3

°), ra

re bio

herms

Bar-channel

HST

FACIES TRACTS

Outer ramp fusulinid wackestone-packstoneMiddle ramp grain-rich packstoneInner ramp amalgamated tidal flatInner ramp tidal-flat-capped wackestoneTidal-flat wackestone-siltstone

SEQUENCE STRATIGRAPHYHigh-frequencysequence

Compositesequence

L 1

HFS

Karst breccia andconglomerate

Reservoir interval

200 ft

Clinoformal, outer ramp fusulinid-crinoidwackestone-packstone

Sequence Stratigraphic Model

Abo

Wichita

LowerClearFork

TubbLandward Basinward

HFS 2.3

HFS 2.2

L 2

L 1

L 3

HFS 2.1

0

0 4 mi

6 km

0

0 4 mi

6 km

QAd4360x

BureauofEconomic

Geology