Is There a Basin-Centered Gas Accumulation

in Cotton Valley Group Sandstones,

Gulf Coast Basin, U.S.A.?

By Charles E. Bartberger, Thaddeus S. Dyman, and Steven M. Condon

U.S. Geological Survey Bulletin 2184-D

U.S. Department of the Interior

U.S. Geological Survey

Geologic Studies of Basin-Centered Gas Systems

Edited by Vito F. Nuccio and Thaddeus S. Dyman

This work funded by the U.S. Department of Energy, National 

Energy Technology Laboratory, Morgantown, W. Va., under 

contracts DE-AT26-98FT40031 and DE-AT26-98FT40032, and by the 

U.S. Geological Survey Central Region Energy Resources Team
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

Any use of trade, product, or fi rm names in this publication

is for descriptive purposes only and does not

imply endorsement by the U.S. Government

This publication is only available online at:

http://geology.cr.usgs.gov/pub/bulletins/b2184-d/

Posted online February 2002, version 1.0
III

Contents

Abstract.......................................................................................................................................................... 1

Introduction ................................................................................................................................................... 1

Data Sources........................................................................................................................................ 3

Acknowledgments........................................................................................................................................ 3

Continuous-Type Gas Accumulations ....................................................................................................... 3

Basin-Centered Gas Accumulations ................................................................................................ 3

Method of Evaluating Potential of Basin-Centered Gas in Cotton Valley Group Sandstones ......... 4

Geologic Setting of Cotton Valley Group................................................................................................... 4

Cotton Valley Group Stratigraphic Nomenclature................................................................................... 6

Cotton Valley Group Depositional Systems .............................................................................................. 9

Regional Framework ........................................................................................................................... 9

Blanket Sandstones of Northern Louisiana .................................................................................. 11

Blanket- and Massive-Sandstone Productive Trends................................................................. 13

Diagenesis of Cotton Valley Group Sandstones .................................................................................... 13

Impact of Diagenetic Mineralogy on Wireline Logs ............................................................................. 15

Source Rocks .............................................................................................................................................. 16

Burial and Thermal History ....................................................................................................................... 16

Abnormal Pressures................................................................................................................................... 17

History of Cotton Valley Group Sandstone Exploration ........................................................................ 17

Comparison of Blanket-Sandstone and Massive-Sandstone Trends ................................................ 20

Blanket-Sandstone Trend................................................................................................................. 20

Massive-Sandstone Trend ............................................................................................................... 24

Limited Data in Published Literature ..................................................................................... 24

Analysis of Drill-Stem-Test and Production-Test Data....................................................... 24

Discussion of Evidence For and Against Basin-Centered Gas ........................................................... 30

Source Rocks and Burial and Thermal History............................................................................. 30

Porosity, Permeability, and Gas-Production Rates ...................................................................... 30

Abnormal Pressures.......................................................................................................................... 30

Gas-Water Contacts.......................................................................................................................... 32

Basin-Centered Gas Potential within Bossier Shale ............................................................................ 34

Conclusions ................................................................................................................................................. 34

References Cited ........................................................................................................................................ 36

Figures

 1. Map of north-central Gulf Coast Basin showing outlines of three Cotton Valley Group 

plays identified by the U.S. Geological Survey in the 1995 National Assessment of 

United States oil and gas resources ......................................................................................... 2
IV

 2. Index map of north-central Gulf Coast Basin showing major tectonic features ............... 5

 3. Chronostratigraphic section of northern Louisiana................................................................ 7

 4. Generalized structure contours on top of Cotton Valley Group sandstone 

across northeastern Texas and northern Louisiana............................................................... 8

 5. Generalized stratigraphic nomenclature of Cotton Valley Group in 

northern Louisiana........................................................................................................................ 9

 6. North-south stratigraphic cross section of Cotton Valley Group across 

northern Louisiana based on data from 15 wells .................................................................. 10

 7. Regional paleogeographic map showing sedimentary environments of 

Cotton Valley Group during deposition of uppermost Cotton Valley sandstones ............ 12

 8–13. Map of northeastern Texas and northwestern Louisiana showing:

 8. Major fields that have produced hydrocarbons from Cotton Valley 

Group sandstones............................................................................................................ 14

 9. Fluid-pressure gradients calculated from shut-in pressures in Cotton 

Valley Group sandstone reservoirs............................................................................... 18

 10. Geographic distribution of abnormally high pressures in Cotton Valley 

Group sandstone reservoirs .......................................................................................... 19

 11. Measured values of porosity and permeability in Cotton Valley Group 

blanket sandstones ......................................................................................................... 21

 12. Initial rates of gas production from Cotton Valley Group 

blanket sandstones ......................................................................................................... 25

 13. Fields productive from Cotton Valley Group sandstones in which gaswater contacts have been identified and reported in published literature ........... 26

 14–15. Map of Caspiana field in northwestern Louisiana in the tight, Cotton Valley 

Group massive-sandstone trend showing:

 14. Initial rate of gas production from Cotton Valley sandstone reservoirs................. 28

 15. Ratio of initial production rate of water to initial production rate of gas 

from Cotton Valley Group sandstones.......................................................................... 29

 16. Schematic diagram of gas-water transition zones in high- and 

low-permeability reservoirs...................................................................................................... 33

Tables

 1. Comparison of two productive trends of Cotton Valley Group sandstones 

in eastern Texas and northern Louisiana ............................................................................... 20

 2. Data on Cotton Valley Group sandstone fields in northern Louisiana ............................... 22
Abstract

The U.S. Geological Survey (USGS), in cooperation with 

the U.S. Department of Energy, is reevaluating the resource 

potential of selected domestic basin-centered gas accumulations. Basin-centered gas accumulations are characterized by 

presence of gas in extensive low-permeability (tight) reservoirs 

in which conventional seals and trapping mechanisms are 

absent, abnormally high or low reservoir pressures exist, and 

gas-water contacts are absent.

In 1995, the USGS assessed one basin-centered gas play 

and two conventional plays within the trend of Jurassic and 

Cretaceous Cotton Valley Group fl uvial-deltaic and barrierisland/strandplain sandstones across the onshore northern Gulf 

of Mexico Basin. Detailed evaluation of geologic and production data provides new insights into these Cotton Valley plays. 

Two Cotton Valley sandstone trends are identifi ed based 

on reservoir properties and gas-production characteristics. 

Transgressive blanket sandstones across northern Louisiana 

have relatively high porosity and permeability and do not 

require fracture stimulation to produce gas at commercial 

rates. South of this trend, and extending westward into eastern 

Texas, massive sandstones of the Cotton Valley trend exhibit 

low porosity and permeability and require fracture stimulation. 

The high permeability of Cotton Valley blanket sandstones is 

not conducive to the presence of basin-centered gas, but lowpermeability massive sandstones provide the type of reservoir 

in which basin-centered gas accumulations commonly occur.

Data on source rocks, including burial and thermal history, are consistent with the interpretation of potential basincentered gas within Cotton Valley sandstones. However, pressure gradients throughout most of the blanket- and massivesandstone trends are normal or nearly normal, which is not 

characteristic of basin-centered gas accumulations. 

The presence of gas-water contacts in at least seven fi elds 

across the blanket-sandstone trend together with relatively 

high permeabilities and high gas-production rates without fracture stimulation indicate that fi elds in this trend are conventional. Within the tight massive-sandstone trend, permeability 

is suffi ciently low that gas-water transition zones are vertically 

extensive and gas-water contacts either have not been encountered or are poorly defi ned. With increasing depth through 

these transition zones, gas saturation decreases and water saturation increases until eventually gas saturations become suffi ciently low that, in terms of ultimate cumulative production, 

wells are noncommercial. Such progressive increase in water 

saturation with depth suggests that poorly defi ned gas-water 

contacts probably are present below the depth at which wells 

become noncommercial. The interpreted presence of gas-water 

contacts within the tight, Cotton Valley massive-sandstone 

trend suggests that gas accumulations in this trend, too, are 

conventional, and that a basin-centered gas accumulation does 

not exist within Cotton Valley sandstones in the northern Gulf 

Basin.

Introduction

The U.S. Geological Survey is reevaluating the potential 

for occurrence of continuous-type basin-centered gas accumulations in selected basins in the United States since completion 

of the USGS 1995 National Petroleum Assessment. This effort, 

which is partly funded by the U.S. Department of Energy, 

might result in identifi cation of new continuous-type gas plays 

and petroleum systems or reevaluation of existing plays.

As part of the 1995 National Assessment of United States 

Oil and Gas Resources by the USGS, Schenk and Viger (1996) 

identifi ed one continuous-type basin-centered gas play and two 

conventional gas plays (fi g. 1) within the Cotton Valley Group 

sandstone trend in eastern Texas and northern Louisiana. The 

purpose of this report is to reevaluate the 1995 USGS play 

defi nitions and parameters for establishing those plays through 

more extensive evaluation of data on reservoir properties, reservoir pressures, gas and water recoveries, gas-production rates, 

and gas-water contacts in Cotton Valley sandstones. Data favorable and unfavorable for the presence of continuous-type basincentered gas accumulations are summarized. No attempt is 

Is There a Basin-Centered Gas Accumulation 

in Cotton Valley Group Sandstones, 

Gulf Coast Basin, U.S.A.?

By Charles E. Bartberger,1 Thaddeus S. Dyman,2 and Steven M. Condon2

1

 Geologic consultant, Denver, Colo.

2

 U.S. Geological Survey, Denver, Colo.

1
Figure 1. Map of north-central Gulf Coast Basin from Schenk and Viger (1996) showing outlines of three Cotton Valley Group plays identifi ed by U.S. Ge

1995 National Assessment of United States oil and gas resources. Shown are the Cotton Valley Blanket Sandstones gas play (4923) identifi ed as a contiCotton Valley Salt Basins gas play (4922) and Cotton Valley Sabine Uplift gas play (4924) identifi ed as conventional gas plays.

0 50 

Mile

96°W 94°W 92°W 90°W 8

34°N

32°N30°N

28°N

OKLAHOMA

TEXAS

ARKANSAS

LOUISIANA

MISSISSIPPI

Gulf of Mexico

4922

4924

4923
made, however, to identify new plays and petroleum systems or 

to assess gas resources for potential plays.

From a regional perspective, two productive trends of 

Cotton Valley sandstones are recognized based on sandstonereservoir properties, gas-production rates, and necessity of 

hydraulic-fracturing treatments to achieve commercial production. Across northernmost Louisiana, so-called Cotton Valley 

blanket sandstones have suffi ciently high porosity and permeability that commercial rates of gas production can be obtained 

without artifi cial well stimulation. South of this area, in northern Louisiana, and extending westward across the Sabine 

uplift into northeastern Texas, sandstones in the Cotton 

Valley massive-sandstone trend have poorer reservoir properties and require hydraulic-fracture treatments to achieve 

commercial rates of gas production. Because basin-centered, 

continuous gas accumulations characteristically occur within 

low-permeability reservoirs, the tight, Cotton Valley massivesandstone trend across northern Louisiana and northeastern 

Texas is an ideal setting in which to look for potential basincentered gas accumulations. 

Data Sources

Interpretations and conclusions presented in this report 

are based on data from published literature and limited conversations with industry personnel, together with geologic and 

engineering data accessible in a publicly available CD-ROM 

database from IHS Energy Group (PI/Dwights Plus, a trademark of Petroleum Information/Dwights, d.b.a. IHS Energy 

Group). PI/Dwights Plus data evaluated for this report are 

current through February 2000. Primary data from PI/Dwights 

Plus pertinent to this study are results of drill-stem and production tests in Cotton Valley sandstones reported for individual 

wells. Because well-completion records depend on information provided by operators, well data in PI/Dwights Plus might 

be incomplete. 

Acknowledgments

This work is funded by the U.S. Department of 

Energy, National Energy Technology Laboratory, Morgantown, W. Va. (contract nos. DE-AT26-98FT40031 and DEAT26-98FT40032), and by the U.S. Geological Survey Central 

Energy Team. Laura Biewick of the USGS provided instruction and assistance in using ArcView software to evaluate 

Cotton Valley well and test data. Gregory Zerrahn and 

Joseph Lott, geologists with Palmer Petroleum, Shreveport, 

La., assisted in obtaining reports, maps, and literature. We 

thank Al Brake, BP Amoco, and Al Taylor, Nomad Geosciences, for providing invaluable information on characteristics 

of Cotton Valley tight-gas accumulations. We acknowledge 

helpful reviews of this manuscript by Chuck Spencer, Curt 

Huffman, and Katharine Varnes of the USGS.

Continuous-Type Gas Accumulations

It is important to identify continuous-type gas accumulations because resource assessment for such gas accumulations 

is conducted using different methodology than that used for 

conventional fi elds. Continuous-type gas accumulations generally occur within an extensive volume of reservoir rock with 

spatial dimensions equal to or exceeding those of conventional 

hydrocarbon plays. The defi nition of continuous gas accumulations used here is based on geology rather than on government 

regulations defi ning low-permeability (tight) gas accumulations. Common geologic and production characteristics of continuous gas accumulations include their occurrence downdip 

from water-saturated rocks, lack of conventional traps or seals, 

reservoir rocks with low matrix permeability, presence of 

abnormal pressures, large in-place volumes of gas, and low 

recovery factors (Schmoker, 1996).

Continuous gas plays were treated as a separate category 

in the U.S. Geological Survey 1995 National Petroleum 

Assessment and were assessed using a specialized methodology (Schmoker, 1996). These continuous plays are diverse 

geologically and fall into several categories including coal-bed 

gas, biogenic gas, fractured-shale gas, and basin-centered gas 

accumulations. This report focuses on the potential for basincentered gas within Cotton Valley sandstones.

Basin-Centered Gas Accumulations

From studies of hydrocarbon-productive basins in the 

Rocky Mountain region, Law and Dickinson (1985) and Spencer (1987) identifi ed characteristics of basin-centered gas 

accumulations that distinguish them from conventional ones. 

Basin-centered gas accumulations:

 1. Are geographically large, spanning tens to hundreds of 

square miles in aerial extent, typically occupying the 

central, deeper parts of sedimentary basins.

 2. Occur in reservoirs with low permeability—generally 

less than 0.1 millidarcy (mD)—such that gas cannot 

migrate by buoyancy. 

 3. Lack downdip gas-water contacts because gas is not 

held in place by buoyancy of water. Consequently, 

water production is low or absent. If water is produced, 

it is not associated with a distinct gas-water contact.

 4. Commonly occur in abnormally pressured reservoirs 

(generally overpressured, but occasionally underpressured).

 5. Contain primarily thermogenic gas, and where overpressure is encountered, the overpressuring mechanism 

is thermal generation of gas.

 6. Occur structurally downdip from water-bearing reservoirs that are normally pressured or occasionally 

underpressured.

 7. Lack traditional seals and trapping mechanisms.

 8. Have gas-prone source rocks proximal to the lowIs There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 3
permeability reservoirs such that migration distances 

are short.

 9. Occur in settings such that the tops of such gas accumulations occur within a narrow range of thermal 

maturity, usually between a vitrinite refl ectance (Ro) of 

0.75 and 0.9 percent.

What causes a basin-centered, continuous gas accumulation to form? The most common scenario involves lowpermeability reservoirs in which overpressure develops in 

response to thermal generation of gas. Gas-prone source 

rocks generally must be associated with, or proximal to, lowpermeability reservoirs, and this sequence of source and reservoir rock must be buried to a depth suffi cient for the source 

rocks to generate gas. Overpressure develops because thermal 

generation of gas occurs at a rate that exceeds the rate at which 

gas is lost updip by migration through the low-permeability 

reservoir. As overpressure develops, any free water in pores of 

the tight reservoir is forced out updip into higher permeability, 

normally pressured, water-bearing strata. Only bound, irreducible water remains in the tight-gas reservoir. Permeability is 

suffi ciently low within the tight reservoir that gas does not 

migrate through it by buoyancy as it does through conventional 

reservoirs with higher permeabilities (Gies, 1984; Spencer, 

1987; Law and Spencer, 1993). Instead, gas migrates slowly 

through the tight-gas reservoir with movement caused by the 

pressure differential between the region of high-pressure gas 

generation and the normally pressured, higher permeability, 

water-bearing rocks updip where gas does migrate upward 

rapidly by buoyancy. Thus, because of its inherent low permeability, a basin-centered gas reservoir itself retards the upward 

migration of gas, in effect forming its own leaky seal, and 

maintaining overpressured conditions.

This scenario probably describes an ideal, end-member 

situation. In some cases, for example, basin-centered gas accumulations have subnormal reservoir pressures resulting from 

signifi cant tectonic uplift of strata in the basin. For a basin that 

is tectonically active and in an intermediate stage of uplift, it 

might be possible to fi nd a basin-centered gas accumulation 

that is normally pressured. It is also possible that particular 

gas accumulations might have only some of the characteristics 

for basin-centered gas described above and that differentiating 

between basin-centered and conventional accumulations could 

be diffi cult and subjective. It is with this understanding that the 

potential for basin-centered gas in Cotton Valley sandstones is 

evaluated. 

Method for Evaluating Potential of 

Basin-Centered Gas in Cotton 

Valley Group Sandstones

One of the main requirements for occurrence of a basincentered, continuous gas accumulation is the presence of a 

regional seal to trap gas in a large volume of rock across 

a wide geographic area. Within that large volume of rock, 

discrete gas accumulations having conventional seals and gaswater contacts are absent, and occurrence of gas often cuts 

across stratigraphic units. In classic basin-centered gas accumulations (Law and Dickinson, 1985; Spencer, 1987; Law and 

Spencer, 1993), the regional seal is provided by the low permeability of the reservoir itself. To evaluate the potential for 

the presence of a continuous gas accumulation within Cotton 

Valley Group sandstones, therefore, it is necessary to examine 

reservoir properties of Cotton Valley sandstones across the 

northern Gulf Coast Basin. Because reservoir properties of 

Cotton Valley sandstones are governed by diagenetic characteristics, which are controlled primarily by depositional environment, it is helpful to understand Cotton Valley depositional 

systems and related diagenetic patterns.

Although gas production from Cotton Valley sandstones 

seems to occur from discrete fi elds, it is necessary to determine 

if those fi elds are separate, conventional accumulations or socalled “sweet spots” within a regional, continuous gas accumulation. Thus, it is essential to understand what characterizes the 

apparent productive limits of existing Cotton Valley gas fi elds, 

including the presence or absence of gas-water contacts. For 

some fi elds in which gas-water contacts are not reported, an 

attempt was made to determine the presence or absence of gaswater contacts by examining fl uid recoveries from drill-stem or 

production tests in wells on the fl anks of those fi elds. The goal 

was to determine if certain Cotton Valley fi elds that produce 

from tight-gas sandstones are fl anked by dry holes that tested 

water only, without gas, suggesting presence of a gas-water 

contact. To analyze test data spatially, data from PI/Dwights 

Plus were imported into ArcView 3.2, running on a desktop 

computer. While viewing the map display, test results from any 

particular well could be examined.

Finally, because continuous gas accumulations often are 

characterized by overpressure associated with thermal generation of gas from source rocks in proximity to low-permeability 

reservoirs, it is important to evaluate the presence and quality 

of potential source rocks, burial and thermal history of those 

source rocks, and reservoir-pressure data.

Geologic Setting of 

Cotton Valley Group 

The Cotton Valley Group is an Upper Jurassic to Lower 

Cretaceous sequence of sandstone, shale, and limestone that 

underlies much of the northern Gulf of Mexico coastal plain 

from eastern Texas to Alabama (fi gs. 2 and 3). Cotton Valley 

strata occur only in the subsurface and form a sedimentary 

wedge that thickens southward into the Gulf Basin from a 

zero edge in southern Arkansas and eastern Texas (fi g. 2). 

The downdip limit of the Cotton Valley Group has not been 

delineated yet by drilling. The depth to top of the Cotton 

Valley ranges from about 4,000 ft below sea level near the 

4 Geologic Studies of Basin-Centered Gas Systems
Figure 2. Index map of north-central Gulf Coast Basin, modifi ed from Dutton and others (1993), showing major tectonic features. Sabine and Monroe u

features during deposition of Cotton Valley Group sediments. Cotton Valley depocenters were located across the entire northern Gulf Basin from eastemovement in East Texas and North Louisiana Salt Basins was contemporaneous with deposition of Cotton Valley Group clastic sediments. The Cotton Vsubsurface sequence of strata with approximate updip limits shown here.

34°N32°N30°N

96°W 94°W 92°W 90°W

LOUISIANA

ARKANSASLOUISIANA

TEXAS

LOUISIANA

MISSISSIPPI

MISSISSIPPI

SALT

BASIN

NORTH

LOUISIANA

SALT

BASIN

MONROE

UPLIFT

SABINE

ARCH

COMANCHEAN SHELF EDGE

EAST

TEXAS

SALT

BASIN

MEXIA-TALCO FAULT ZONE FAULT ZONE

GINGER

FAULT ZONE

MT ENTERPRISE

FAULT ARKANSAS ZONE SOUTH

FAULT

PICKENS

APPROX DOWNDIP LIMIT

OF COTTON VALLEY GROUP

SANDSTONE

0 20 40 60 80

MILES

GULF OF MEXICO

APPROX UPDIP LIMIT

OF COTTON VALLEY GROUP

(SWAIN, 1944)

(THOMAS & MANN, 1966)
updip zero edge to more than 13,000 ft below sea level along 

the southern margins of the East Texas and Louisiana Salt 

Basins (fi gs. 2 and 4). In southeastern Mississippi, the top 

of the Cotton Valley occurs at nearly 20,000 ft below sea 

level. The greatest thickness of Cotton Valley rocks penetrated 

exceeds 5,000 ft in southeastern Mississippi (Moore, 1983). 

The Cotton Valley Group and overlying Travis Peak 

(Hosston) Formation represent the fi rst major infl ux of terrigenous clastic sediments into the Gulf of Mexico Basin following its initial formation during continental rifting in Late Triassic time (Salvador, 1987; Worrall and Snelson, 1989). Earliest sedimentary deposits in East Texas and North Louisiana 

subbasins (fi gs. 2 and 3) include upper Triassic nonmarine 

red beds of the Eagle Mills Formation, the thick Middle and 

Upper Jurassic evaporite sequence known as Werner Formation (anhydrite) and Louann Salt, and the nonmarine Norphlet 

Formation. Following a major regional marine transgression 

across the Norphlet, Upper Jurassic Smackover Formation 

regressive carbonates were deposited, capped by red beds and 

evaporites of the Buckner Formation (fi g. 3). A subsequent 

minor marine transgression is recorded by the Gilmer Limestone or Cotton Valley Formation in eastern Texas, although 

equivalent facies in northern Louisiana and Mississippi are 

terrigenous clastics known as the Haynesville Formation. The 

marine Bossier Shale, lowermost formation of the Cotton 

Valley Group (fi gs. 3 and 5) was deposited conformably on 

Gilmer-Haynesville strata.

Louann Salt became mobile as a result of sediment loading and associated basinward tilting. Salt movement was initiated during Smackover carbonate deposition and became more 

extensive with infl ux of Cotton Valley clastics (McGowen and 

Harris, 1984). Many Cotton Valley and Travis Peak fi elds 

in eastern Texas, Louisiana, and Mississippi are structural or 

combination traps associated with Louann Salt structures. Salt 

structures range from small, low-relief salt pillows to large, 

piercement domes (McGowen and Harris, 1984; Kosters and 

others, 1989).

The Sabine uplift is a broad, low-relief, basement-cored 

arch separating the East Texas and North Louisiana Salt Basins 

(fi gs. 2 and 4). With vertical relief of 2,000 ft, the Sabine uplift 

has a closed area exceeding 2,500 mi2 (Kosters and others, 

1989). Isopach data across the uplift indicate that it was a positive feature during deposition of Louann Salt in the Jurassic 

but that primary uplift occurred in late, mid-Cretaceous (101 

to 98 Ma) and early Tertiary time (58 to 46 Ma) (Laubach and 

Jackson, 1990; Jackson and Laubach, 1991). As a high area for 

the past 60 m.y., the Sabine uplift has been a focal area for 

hydrocarbon migration in the northern Gulf Basin during that 

time. Numerous smaller structural highs on the uplift in the 

form of domes, anticlines, and structural noses provide traps 

for hydrocarbon accumulations, including many gas fi elds 

in Cotton Valley sandstones. Origins of these smaller structures have been attributed to salt deformation and small igneous intrusions, as summarized by Kosters and others (1989). 

Because the Louann Salt is thin across the Sabine uplift, 

Kosters and others (1989) suggest that most of the smaller 

structures across the Sabine uplift developed in association 

with igneous activity.

Cotton Valley Group 

Stratigraphic Nomenclature

Since the fi rst penetration of Cotton Valley strata in northern Louisiana in 1927, complex informal stratigraphic nomenclature developed as numerous Cotton Valley oil and gas fi elds 

were discovered across the region through the 1940’s. Nomenclature became complex because of local stratigraphic complexities within Cotton Valley strata in northern Louisiana 

and also because of regional variations in Cotton Valley 

depositional systems across the northern Gulf Basin. Terminology established by Swain (1944) was used until the complete revision of Cotton Valley stratigraphy by Thomas and 

Mann (1963) and Mann and Thomas (1964). Most subsequent 

reports, including the classic work of Collins (1980), have 

used Mann-Thomas terminology. Refi nements to that terminology have been contributed by Coleman and Coleman 

(1981) and Eversull (1985). 

Cotton Valley lithofacies and associated stratigraphic 

nomenclature in northern Louisiana are shown in fi gures 5 

and 6. The basal formation of the Cotton Valley Group is the 

Bossier Shale, a dark, calcareous, fossiliferous, marine shale. 

In eastern Texas, isolated turbidite sandstones occur within the 

Bossier Shale (Collins, 1980). Overpressured gas currently is 

being produced from these sandstones in a rapidly developing 

new play (PI Dwights Drilling Wire, Jan. 3, 2000; Exploration 

Business Journal, 2nd quarter, 2000). Completely encased in 

marine shale, these gas-charged sandstones might represent a 

continuous gas accumulation. 

The Bossier Shale grades upward into Cotton Valley sandstones with interbedded shales. These sandstones consist of 

stacked barrier-island, offshore-bar, strandplain, and fl uvialdeltaic sandstones and are referred to as the Terryville massive-sandstone complex in northern Louisiana by Coleman and 

Coleman (1981). In eastern Texas, the stratigraphically equivalent unit is called Cotton Valley Sandstone, and it consists 

of braided-stream, fan-delta, and wave-dominated-delta sandstones (Wescott, 1983; Coleman, 1985; Dutton and others, 

1993). Across the Cotton Valley hydrocarbon-productive trend 

in eastern Texas and northern Louisiana, the Terryville or 

Cotton Valley Sandstone averages about 1,000 to 1,400 ft in 

thickness (Finley, 1984; Presley and Reed, 1984). Sand deposition was interrupted in Early Cretaceous time by a regional 

transgressive event marked by deposition of the Knowles Limestone (fi gs. 5 and 6). In updip areas of eastern Texas and 

southern Arkansas, the Knowles Limestone pinches out, and 

clastic rocks of the Travis Peak, or equivalent Hosston, Formation directly overly Cotton Valley sandstones (fi gs. 3, 5, and 

6). Saucier (1985) interprets the Knowles Limestone as the 

uppermost formation of the Cotton Valley Group, but Coleman 

6 Geologic Studies of Basin-Centered Gas Systems
Figure 3. Chronostratigraphic section of northern Louisiana modifi ed from Shreveport Geological Society (1987). Subdivisions 

of Cotton Valley Group shown in fi gure 5. 

CHRONOSTRATAGRAPHIC SECTION OF NORTH LOUISIANA

SYSTEM

SERIES

STAGE GROUP FORMATION

TERTIARY

PALEOGENE

PALEOGENE

EOCENE

AGE

(Ma)

GULFIAN

UPPER CRETACEOUS

COMANCHEAN

LOWER CRETACEOUS

COAHUILAN

JURASSIC

UPPER MIDDLE LOWER UPPER

TRIASSIC

YPRESIAN

THANETIAN

DANIAN

MAASTRICHTIAN

CAMPANIAN

SANTONIAN

CONIACIAN

TURONIAN

CENOMANIAN

ALBIAN

APTIAN

BARREMIAN

HAUTERIVIAN

VALANGINIAN

BERRIASIAN

TITHONIAN

KIMMERIDGIAN

OXFORDIAN

CALLOVIAN

BATHONIAN

BAJOCIAN

AALENIAN

TOARCIAN

PLIENSBACHIAN

SINEMURIAN

HETTANGIAN

RHAETIAN

WILCOX WILCOX

MIDWAY MIDWAY

NAVARRO

TAYLOR

AUSTIN

EAGLE FORD

WOODBINE

WASHITA

TRINITY

GLEN

ROSE

FREDRICKSBURG

HIATUS

HIATUS

HIATUS

ARKADELPHIA

NACATOCH

EAGLE FORD

SARATOGA

ANNONA

OZAN

TOKIO

AUSTIN

TUSCALOOSA

PALUXY WASHITA-FREDERICKSBURG

MOORINGSPORT

FERRY LAKE ANHYDRITE

RODESSAJAMES PINE ISLAND

PETTET (SLIGO) MBR

SLIGO

HOSSTON

(TRAVIS PEAK)

HAYNESVILLE-BUCKNER

SMACKOVER

NORPHLET

LOUANN

WERNER

EAGLE MILLS

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

MILLIONS OF YEARS

COTTON VALLEY (See figure 5)

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 7
Figure 4. Generalized structure contours on top of Cotton Valley Group sandstone across northeastern Texas and northern Louisiana, modifi ed from Finle

sandstone has been designated as “tight-gas sandstone” in all counties shown on this map with exception of 15 gas fi elds in northern Louisiana (fi g. 8).

TEXAS LA

0 10 20 30 40 50

Miles

Contour Interval: 1000 feet

OKLAHOMA

ARKANSAS

FANNIN

COLLIN

LAMAR

HUNT

HOPKINS

RAINS

WOOD

ROCKWALL

DELTA

DALLAS

KAUFMAN VAN ZANDT

ELLIS

NAVARRO

HENDERSON

LIMESTONE

FREESTONE

ANDERSON

LEON

HOUSTON

MADISON

TRINITY

BRAZOS

ROBERTSON

MILAM

FALLS ANGELINA

NACODOCHES

CHEROKEE

SMITH

UPSHUR

GREGG

RUSK

RED RIVER

FRANKLIN TITUS

CAMP

MORRIS

BOWIE

CASS

MARION

HARRISON

PANOLA

SHELBY

SAN

AGUSTINE

SABINE

SABINE

VERNON RAPIDES

DE SOTO RED RIVER

NATCHITOCHES

BIENVILLE

WINN

JACKSON

GRANT

CADDO

BOSSIER

WEBSTERCLAIBORNE LINCOLNUNION

MOREH

RICH

OUACHITA 

CALDWELL

LA SALLE

CATAHO

FRA

-8000

-4000

-5000

-6000

-7000

-8000 -8000

-9000

-10,000

-5000

-10,000

-11,000

-12,000

-13,000

-6000 -7000

-8000

-10,000

-14,000

-15,000

-11,000

-12,000

-13,000

-11,000

-7000

-9000

-10,000

-6000

-5000

-4000

-13,000

-12,000

-11,000

-9000
and Coleman (1981) include the stratigraphically higher Calvin 

Sandstone, Winn Limestone, and unnamed sands and shales 

within the Cotton Valley Group (fi gs. 5 and 6). 

Cotton Valley Group 

Depositional Systems

Regional Framework

From eastern Texas to Mississippi, stacked barrier-island, 

strandplain, and fl uvial-deltaic sandstones, known as Cotton 

Valley or Terryville Sandstone, refl ect infl ux of sands from 

a number of depocenters. Evolution of Cotton Valley depocenters and associated paleogeography across northern Louisiana 

are described and illustrated by Coleman and Coleman (1981), 

who subdivided the Terryville Sandstone into four depositional 

“events” (fi g. 6) based on widespread shale breaks. Across 

south-central Mississippi, Moore (1983) shows three sequential paleogeographic reconstructions of Cotton Valley Group 

sandstone deposition. Although the setting was similar, concise 

paleogeographic reconstructions have not been published for 

the East Texas Basin; however, McGowen and Harris (1984) 

and Wescott (1985) provide data from which basic paleogeographic maps can be constructed. Figure 7 is a regional paleoFigure 5. Generalized stratigraphic nomenclature of Cotton Valley Group (patterned units) in northern 

Louisiana, modifi ed from Coleman and Coleman (1981). Schuler Formation and equivalents were assigned to 

Lower Cretaceous in mid 1980’s (Herrmann and others, 1991). Prior to that time, entire Cotton Valley Group was 

considered to be Late Jurassic in age. CRETACEOUS JURASSIC COTTON VALLEY GROUP

WINN LS

MASSIVE

SANDSTONE

COMPLEX OF CALVIN SS.

HOSSTON FORMATION

UNNAMED SANDS & SHALES

KNOWLES LIMESTONE

BLANKET

SANDSTONES

MASSIVE SANDSTONE

COMPLEX OF

TERRYVILLE SS.

HICO

SHALE

BOSSIER SHALE

HAYNESVILLE, BUCKNER, AND

SMACKOVER FORMATIONS

SCHULER FM

DOWNDIP UPDIP

(SOUTH) (NORTH)

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 9
geographic map of upper Cotton Valley depositional systems 

(equivalent to Terryville IV of Coleman and Coleman, 1981) 

across the northern Gulf Basin from eastern Texas to Mississippi based on data integrated from these various workers. 

As shown in fi gure 7, Cotton Valley fl uvial-deltaic depocenters were located in present-day northeastern Texas, 

south-central Mississippi, and along the Louisiana-Mississippi 

border. The system along the Louisiana-Mississippi border 

represents the ancestral Mississippi River and was a locus 

of major clastic infl ux. Large quantities of sand delivered 

to the marine environment by this system were transported 

westward by longshore currents producing an extensive eastwest barrier-island or strandplain complex (Thomas and 

Mann, 1966). Vertical stacking of barrier-island/strandplain 

sands through time resulted in accumulation of the Terryville 

massive-sandstone complex (fi gs. 6 and 7). The east-west 

barrier-island complex across northern Louisiana sheltered a 

lagoon to the north from open-marine waters to the south 

(Thomas and Mann, 1966). The Hico Shale accumulated in the 

lagoon while fl uvial and coastal-plain sandstones and shales of 

the Schuler Formation were deposited in continental environments north of the lagoon (fi gs. 6 and 7). Development of 

a similar, but smaller, lagoon associated with barrier islands—

formed from longshore-transported sands in south-central Mississippi—was documented by Moore (1983) (fi g. 7). In eastern 

Texas, during the earliest phase of Cotton Valley Sandstone 

deposition, small fan deltas developed along the updip margin 

of the East Texas Basin (McGowen and Harris, 1984; Wescott, 

1985; Black and Berg, 1987). The drainage system was immature with small fan deltas formed by numerous small streams. 

According to McGowen and Harris (1984), fan-delta deposition persisted through Cotton Valley time along the western 

margin of the East Texas Basin where fan-delta deposits characterize most of the Cotton Valley Sandstone interval. Along 

the northern fl ank of the East Texas Basin, in the region 

of the present-day Sabine uplift, a mature drainage system 

Figure 6 (above and facing page). North-south stratigraphic cross section of Cotton Valley Group across 

northern Louisiana based on data from 15 wells. Section is modifi ed from Coleman and Coleman (1981) to 

show details of Cotton Valley blanket sandstones as identifi ed and described by Eversull (1985) and Thomas 

and Mann (1963). Arrows indicate stratigraphic range of blanket sandstones. Line of cross section shown 

in fi gures 7 and 8. 

SOUTH

1

A

23 4 56 7 8 9

WINN LIMESTONE

CALVIN

SANDSTONE TERRYVILLE

KNOWLES LIMESTONE

10 Geologic Studies of Basin-Centered Gas Systems
developed as fan deltas prograded basinward and evolved into 

a wave-dominated delta system. Sandstones of the lower part 

of the Cotton Valley comprising this delta system are referred 

to informally as the Taylor sandstone, according to Wescott 

(1985). After Taylor sand deposition was terminated by a subregional transgressive event, delta progradation resumed with 

development of a more elongate, fl uvial-dominated system in 

the upper part of the Cotton Valley (fi g. 7), referred to as the 

Lone Oak delta by Kast (1983). 

Blanket Sandstones of Northern Louisiana

In northern Louisiana, at least 20 distinct tongues of sandstone extend landward from barrier-island deposits of the Terryville massive-sandstone complex and become thinner northward before pinching out into shales of the Hico lagoon, as 

shown in fi gure 6. Some of these sandstones have limited 

geographic extent covering only part of the lagoon, whereas 

others extend across most or all of the lagoon and interfi nger 

with continental deposits of the Schuler Formation on the 

landward side of the lagoon (Coleman and Coleman, 1981; 

Eversull, 1985). These sandstones have been interpreted as 

transgressive deposits with sand being derived from Terryville 

barrier islands and transported landward into the Hico lagoon 

during periods of relative sea-level rise and (or) diminished 

sediment supply (Coleman and Coleman, 1981; Eversull, 

1985). These transgressive sandstones have signifi cantly better 

porosity and permeability than Terryville massive sandstones 

from which they were derived and have been prolifi c producers of oil and gas from structural, stratigraphic, and combination traps discovered in the 1940’s, 1950’s, and 1960’s 

across northern Louisiana (Collins, 1980; Bebout and others, 

1992). Referred to informally as “blanket” sandstones (Eversull, 1985), they can be correlated readily across northern 

Louisiana, and, as shown in fi gure 6, they were given informal 

names by operators during drilling in the 1940’s and 1950’s 

(Sloane, 1958; Thomas and Mann, 1963; and Eversull, 1985). 

1000

500

0

Feet

10 5 0

Miles

NORTH

15

A'

10 11 12 13 14

HOSSTON FM

MASSIVE

SANDSTONES I

II

III

IV HICO SHALE

SCHULER FORMATION

(Alluvial, coastal plain,

fluvial deltaic

(Barrier Islands

offshore bars)

Cadeville

B C

D Bodcaw

Vaughn Price

McGreary

Bolinger

Davis

E

Justiss

Ardis

(Lagoon/bay)

Roseberry?

Sexton

Taylor

Tucker

BOSSIER SHALE

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 11
Figure 7. Regional paleogeographic map showing sedimentary environments of Cotton Valley Group during deposition of uppermost Cotton Valley s

IV sandstone of Coleman and Coleman, 1981). Map synthesized from data of Thomas and Mann (1966), Coleman and Coleman (1981), Moore (1983), M(1984), Wescott (1985), and Eversull (1985). Location of north-south stratigraphic cross section of Cotton Valley Group across northern Louisiana in fi gby 15 numbered wells.

0 50 25 75 100

Miles Gulf of Mexico

TX

OK AR

DETAIL AL

AREA

LOCATION MAP

NM TN

LA

MS

ANCESTRAL M

RIVER COTTO

DEPOCE

LONE OAK DELTA

COTTON VALLEY

DEPOCENTER

ARKANSAS

LOUISIANA

TEXAS LOUISIANA

LOUISIANA

MISSISSIPPI

OKLAHOMA

TEXAS

MAXIMUM SOUTHERN

EXTENT

TERRYVILLE MASSIVE O SANDSTONES F BARRIER ISLAND BARRIER ISLAN

BAY/LAGO

HICO LAGOON

A

A' 15

14

13

12

11

10 9

8

7

5

4 6

2

3

1

UPPER COTTON VALLEY GROUP PALEOGEOGRAPHY
Based on isopach map trends, Eversull (1985) identifi ed 

two groups of blanket sandstones. Geographically more extensive sandstones of the fi rst group span most of the Hico lagoon 

and often interfi nger with continental deposits of the Schuler 

Formation. These sandstones generally are 30 to 70 ft thick 

and can reach a thickness of 140 ft toward the south where 

they merge with barrier-island sandstones of the Terryville 

massive-sandstone complex. Blanket sandstones of the second 

group generally are less than 30 ft thick, have limited geographic extent, and most commonly occur in the eastern part 

of the Hico lagoon proximal to the fl uvial-deltaic source. 

These sandstones pinch out northward into shales of the 

Hico lagoon. Transgressive, blanket sandstones of both groups 

collectively have signifi cantly higher porosity and permeability than barrier-island sandstones of the Terryville massivesandstone complex to the south (Collins, 1980; Bebout and 

others, 1992).

Blanket- and Massive-Sandstone 

Productive Trends

Signifi cant differences in reservoir properties between 

transgressive, blanket sandstones to the north and massive, 

barrier-island sandstones to the south defi ne two different 

hydrocarbon-productive trends of Cotton Valley sandstones 

(fi g. 8). Blanket sandstones have higher porosity and permeability than Terryville massive sandstones to the south. Eversull (1985) reported that blanket sandstones are cleaner and 

better sorted. She attributed their superior reservoir properties 

to high-energy reworking during transgressive events. Coleman (1985), however, reported that blanket sandstones exhibit 

an increase in calcite cement and clay content northward 

toward their pinch-out edges, and that superior reservoir 

properties occur because (1) clays inhibited precipitation of 

quartz overgrowths and (2) secondary porosity was generated 

through widespread dissolution of calcite cement. Absence of 

detrital clay coatings on sand grains in high-energy barrierisland sandstones of the Terryville massive-sandstone complex to the south, however, permitted widespread precipitation of quartz cement as syntaxial overgrowths, resulting in 

nearly complete occlusion of porosity (Sloane, 1958; Coleman and Coleman, 1981). Whatever the cause of porosity differences, blanket sandstones generally have suffi cient porosity 

and permeability to fl ow gas or liquids on open-hole drillstem tests (DST’s) and to produce gas without fracture-stimulation treatment (Collins, 1980; Bebout and others, 1992). 

Terryville massive sandstones to the south and west, however, 

have such poor reservoir properties that they generally do 

not fl ow gas or liquids during DST’s, and they require 

hydraulic-fracture treatments before commercial production 

can be achieved. 

Diagenesis of 

Cotton Valley Group Sandstones

Because understanding reservoir mineralogy is critical 

to successful wireline-log analysis and design of fracturestimulation treatments in Cotton Valley Group sandstones, 

considerable attention has been devoted to understanding diagenetic patterns of Cotton Valley sandstones, especially in 

the low-permeability, Cotton Valley massive-sandstone trend. 

Focusing on those sandstones in eastern Texas, Wescott (1983) 

reported that Cotton Valley sandstones are very fi ne grained, 

well-sorted quartz arenites and subarkoses with monocrystalline quartz and feldspar being the primary framework components. Principal cements include quartz, calcite, clays, and iron 

oxides. In unraveling the complex diagenetic history of these 

sandstones, Wescott (1983) interpreted two major diagenetic 

sequences. The most common sequence is (1) formation of 

clay coatings—primarily chlorite—on framework grains, usually covering grains partially, not completely, (2) precipitation 

of syntaxial quartz overgrowths on quartz grains, (3) dissolution of unstable grains, most commonly feldspars, (4) precipitation of clays, primarily illite and chlorite with minor kaolinite, (5) precipitation of calcite cement in both relict primary 

pores and secondary pores, and (6) large-scale replacement 

of grains and cements by calcite, resulting in poikilotopic 

texture in which a few relict quartz grains are “fl oating” in 

calcite. In the other, less-common diagenetic sequence, which 

occurs primarily in cleaner, coarser grained sandstones, calcite 

cementation commenced early and progressed to yield a fabric 

with widespread replacement of grains by calcite. 

Wescott (1983) classifi ed Cotton Valley sandstones into 

three general groups on the basis of primary depositional 

texture and resulting diagenetic characteristics. In general, 

Wescott (1983) found that clean, well-sorted sands deposited 

in high-energy environments (type I) generally are nearly completely cemented by quartz and (or) calcite, have little or no 

porosity and permeability, and provide little reservoir potential. In some cases, these sandstones exhibit preservation of 

minor amounts of primary intergranular porosity from presence of authigenic chlorite coats (Hall and others, 1984). In 

sands deposited in lower energy environments where abundant 

detrital clays remained (type II), nucleation of quartz overgrowths generally was inhibited by clays. Most clay-bearing 

sandstones, however, contain signifi cantly large amounts of 

clay, and although abundant microporosity is associated with 

these clays, permeability generally is low. Highest porosities, 

according to Wescott (1983), occur in type-III sandstones, 

which developed abundant secondary porosity from dissolution of unstable grains and calcite cement. Hall and 

others (1984), however, reported that dissolution of unstable 

grains often is incomplete, secondary pores generally are 

poorly interconnected, and these sandstones, too, have poor 

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 13
Figure 8. Map of northeastern Texas and northwestern Louisiana showing major fi elds that have produced hydrocarbons from Cotton Valley Group sandsto

productive trends are recognized based on reservoir properties and resulting producing capabilities of Cotton Valley sandstone reservoirs. Fifteen fi elds excdesignation by FERC in 1980 are shown in solid dark-gray shading. Map modifi ed from Collins (1980) and White and others (1992). Location of north-south strCotton Valley Group across northern Louisiana in fi gure 6 is illustrated by 15 numbered wells.

0 

M

Cotton Valley sandston(designated tight gas bCotton Valley sandston(excluded from 1980 FECotton Valley tight, mas(low porosity & permeaCotton Valley blanket-s(good porosity & permeEast Texas & Louisiana 

Kaufman Gulf of Mexico

TX LA

OK AR

MS AL

LOCATION MAP

DETAIL

AREA

SABINE UPLIFT

NORTH

LOUSIANA

SALT BA

ARKANSAS

TEXAS LOUISIANA

EAST

TEXAS

SALT

BASIN

Woodlawn

Blocker

Oak Hill

Dirgin

Carthage

BethanyLongstreet

GreenwoodWaskom

Longwood

Dixie

Benton

Sligo

Sentell

Caspiana

Elm Grove

LakeBistineau

Plain

Dealing

Rocky

Mount

Ivan

S Sarepeta

Shongaloo

CottonValley

Haynesville

E Haynesville

Blackburn

Lisbon

W Lisbon

Homer

Minden

Leatherman

Creek

Ada

Sibley Bryceland

BearCreek

Athens

SugarCreek

Terryville

Rustin

Clay

Vernon

Tremont

Calhoun

Cadeville

Cheni

S D

CarlN Ca

S Downsville

Downsville

Choudrant

D'Arbonne

Unionville

Hico Knowes

NE Lisbon

A

A' 15

14

13

12

11 10

9

8

7

6

5

4 3

2

1

Frierson
permeability and require fracture stimulation to produce gas 

commercially.

In northern Louisiana, as interpreted by Russell and 

others (1984), the upper Cotton Valley Bodcaw Tongue of the 

Terryville Sandstone at Longwood fi eld on the eastern fl ank 

of the Sabine uplift experienced a virtually identical diagenetic 

history to that described for Cotton Valley sandstones in eastern Texas by Wescott (1983). Like Wescott (1983), Russell and 

others (1984) reported that nucleation of quartz overgrowths 

was inhibited by presence of clays, but the quantity of porefi lling clays generally is so large that permeability is low 

despite presence of high microporosity. Also, as in eastern 

Texas, the best reservoir sandstones are those that have 

low clay content and developed abundant secondary porosity 

through dissolution of unstable grains and cement. Similar 

diagenetic patterns in northern Louisiana also were reported 

for Cotton Valley sandstones at Frierson fi eld by Sonnenberg 

(1976) and for the lowermost part of the Terryville Sandstone 

(the informal Taylor sandstone) at Terryville fi eld by Trojan 

(1985). In addition to authigenic constituents reported in eastern Texas and northern Louisiana, Trojan (1985) also found 

small amounts of authigenic pyrite in Taylor sandstones at 

Terryville fi eld. Pyrite occurs as small silt-size clusters (framboids). It is volumetrically the least abundant authigenic mineral reported by Trojan (1985), but its presence is signifi cant 

because of its effect on wireline-log measurements of formation resistivity. 

Impact of Diagenetic Mineralogy 

on Wireline Logs

The complex diagenetic mineralogy of tight Cotton Valley 

sandstones prohibits use of standard calculation procedures in 

reservoir evaluation with wireline logs. The main diffi culty 

is that properties of certain diagenetic constituents result in 

abnormally low resistivity measurements, which lead to such 

high calculated water saturations that productive zones appear 

to be wet. Major factors contributing to abnormally low resistivities in tight Cotton Valley sandstones include bound water 

associated with pore-fi lling clays or clay coatings and conductive authigenic minerals such as pyrite and ankerite (Janks and 

others 1985; Turner, 1997). 

Pore-lining and pore-fi lling clays have exceptionally high 

ratios of surface area to volume. Large surface area and high 

cation-exchange capacity of clays result in formation of a 

double ionic layer on clay surfaces (Almon, 1979; Snedden, 

1984). This bound double layer can be signifi cantly more 

conductive than pore waters, resulting in abnormally low 

measured resistivities, especially with induction logs (Almon, 

1979; Wescott, 1983). Highly conductive authigenic minerals, 

such as ankerite and pyrite, in Cotton Valley sandstones also 

cause abnormally low resistivities. Trojan (1985) found that 

pyrite concentrations as low as 1 percent in Cotton Valley 

sandstones had a dramatic effect on resistivity measurements 

and hence on calculated water saturations. Standard calculation methods showed that pyrite-bearing sandstones at Terryville fi eld in northern Louisiana had water saturations in 

excess of 100 percent. Trojan (1985) showed that if these sandstones were pyrite-free, calculated water saturations would be 

closer to 50 percent. Although water saturations in productive 

Cotton Valley sandstones commonly are 25 to 30 percent, 

water-free gas production has been achieved from zones with 

calculated water saturations as high as 60 percent (Nangle and 

others, 1982; Wilson and Hensel, 1984; Dutton and others, 

1993). 

Porosity measurements from wireline logs also can be 

affected adversely from diagenetic mineral constituents in 

Cotton Valley sandstones. In a study of Taylor sandstones 

(fi g. 6) at Terryville fi eld in northern Louisiana, Ganer (1985) 

demonstrated the negative impact of authigenic carbonates on 

porosity measurements from wireline logs. Located within the 

porous, permeable blanket sandstone trend, Terryville fi eld 

was discovered in 1954 with production from the Cotton 

Valley “D” sandstone (fi g. 6), one of the blanket sandstones. 

The Taylor sandstone occurs in the lower part of the Cotton 

Valley Sandstone interval, and its productive potential at Terryville fi eld was not discovered until 1978. Unlike the stratigraphically higher blanket sandstones, the Taylor sandstone 

has relatively poor reservoir properties similar to those of 

tight Cotton Valley massive sandstones to the south. Like 

Wescott (1983), Ganer (1985) found that, although the Taylor 

sandstone is predominantly a quartz sandstone, it contains 

authigenic carbonate cement and locally can be composed of 

more than 50 percent carbonate resulting in a poikilotopic 

texture. With abundant secondary porosity from carbonate dissolution, these carbonate-rich sandstones are the best gas producers within the Taylor sandstone interval at Terryville fi eld. 

Ganer (1985) identifi ed several different carbonate minerals 

in Taylor sandstones, including calcite, ankerite, and siderite. 

Grain densities of these minerals are 2.71, 3.00, and 3.96 

g/cm3, respectively. If porosity logs based on a sandstone 

matrix (grain density of 2.65 g/cm3) are run across an interval, 

such as the Taylor sandstone, containing abundant carbonate 

constituents with higher densities, measured porosity values 

will be pessimistic. Working with 420 ft of conventional core 

from four wells at Terryville fi eld, Ganer (1985) reported sandstone intervals with abundant carbonate constituents where 

log-measured porosities were close to zero, but core-measured 

porosities exceeded 6 percent. With complex effects of diagenetic minerals on both porosity and resistivity measurements from wireline logs, Ganer (1985) showed that a single 

porosity/water saturation limit is not suitable for evaluating 

productive potential of Cotton Valley sandstones at Terryville 

fi eld. Ganer’s conclusions probably are applicable to most, or 

all, of the tight, Cotton Valley massive-sandstone trend across 

northeastern Texas and northern Louisiana. 

In comparing core-derived reservoir properties with 

wireline-log measurements for Cotton Valley sandstones from 

Carthage fi eld in eastern Texas, Wilson and Hensel (1984) 

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 15
reported that no apparent relationship exists between porosity 

and permeability. From core analyses, they noted that it is not 

uncommon to fi nd a sandstone interval with 10 percent porosity and 1 to 3 mD permeability adjacent to a zone with similar 

porosity but with permeability less than 0.05 mD. Similarly, 

Ganer (1985) reported that Taylor sandstones with 8 percent 

porosity at Terryville fi eld in northern Louisiana have permeabilities ranging from 0.01 to 13 mD. For Carthage fi eld, 

Wilson and Hensel (1984) also noted that empirically derived 

values of cementation factor (m) and saturation exponent (n), 

used in calculation of water saturation, vary signifi cantly from 

zone to zone. Wilson and Hensel (1984) derived general empirical values of m and n for Carthage fi eld area to achieve more 

accurate log-derived estimates of water saturation. Because of 

such diffi culties in determining water saturations from wireline 

logs, Presley and Reed (1984) stress that gas-pay cutoff values 

should be based on experience by operators in a given area. 

A consequence of diffi culties in accurate reservoir evaluation from conventional log analysis, of course, is that intervals 

capable of producing gas might be bypassed because of high 

calculated water saturations. For this study, the signifi cance 

of these diffi culties with wireline logs in tight Cotton Valley 

sandstones is that logs are of limited value in differentiating 

between gas-productive and wet intervals and therefore in 

identifying gas-water contacts on the fl anks of Cotton Valley 

fi elds. 

Source Rocks

Little information has been published on source rocks for 

hydrocarbons produced from Cotton Valley reservoirs in northern Louisiana and eastern Texas. In studying the overlying 

Travis Peak Formation in eastern Texas, Dutton (1987) showed 

that shales interbedded with Travis Peak sandstone reservoirs 

were deposited in fl uvial-deltaic settings where organic matter 

commonly is oxidized and not preserved. With measured 

values of total organic carbon (TOC) in Travis Peak shales 

generally less than 0.5 percent, these shales are not considered 

as potential hydrocarbon source rocks (Tissot and Welte, 

1978). Dutton (1987) suggested that the most likely sources 

for hydrocarbons in Travis Peak reservoirs in eastern Texas 

are laminated, lime mudstones of the lower member of the 

Jurassic Smackover Formation and prodelta and marine shales 

of the Bossier Shale, basal formation of the Cotton Valley 

Group (fi g. 3). Sassen and Moore (1988) demonstrated that 

Smackover carbonate mudstones are a signifi cant hydrocarbon 

source rock, charging various reservoirs in Mississippi and 

Alabama, and Wescott and Hood (1991) documented the Bossier Shale as a signifi cant source rock in eastern Texas. Presley 

and Reed (1984) suggested that gray to black shales interbedded with Cotton Valley sandstones, as well as the underlying 

Bossier Shale, probably are the source for gas in Cotton Valley 

Sandstone reservoirs. Coleman and Coleman (1981) agreed 

with this interpretation for Cotton Valley sandstone reservoirs 

in northern Louisiana, stating that “hydrocarbons were generated from neighboring source beds.”

In summary, despite limited source-rock data, it seems 

likely that adequate hydrocarbon source rocks occur in the 

Bossier Shale immediately beneath Cotton Valley sandstones 

and also in stratigraphically lower Smackover carbonate mudstones (fi g. 3).

Burial and Thermal History

In a study of diagenesis and burial history of the Travis 

Peak Formation in eastern Texas, Dutton (1987) reported that 

measured vitrinite refl ectance (Ro) values for Travis Peak 

shales generally range from 1.0 to 1.2 percent. This indicates 

that these rocks have passed through the oil window (Ro = 0.6 

to 1.0 percent) and are approaching the level of onset of drygas generation (Ro = 1.2 percent) (Dow, 1978). A maximum 

Ro of 1.8 percent was measured in the deepest sample from 

a downdip well in Nacogdoches County, Texas. Despite thermal maturity levels reached by Travis Peak shales, the small 

amount, and gas-prone nature, of organic matter in these shales 

precludes generation of oil, although minor amounts of gas 

might have been generated (Dutton, 1987). 

In the absence of actual measurements of Ro, values 

of Ro can be estimated by plotting burial depth of a given 

source-rock interval versus time in conjunction with an 

estimated paleogeothermal gradient (Lopatin, 1971; Waples, 

1980). Dutton (1987) presented burial-history curves for tops 

of the Travis Peak Formation, Cotton Valley Group, Bossier 

Shale, and Smackover Formation for seven wells on the crest 

and western fl ank of the Sabine uplift. The burial-history 

curves show total overburden thickness through time and use 

present-day compacted thicknesses of stratigraphic units. Sediment compaction through time was considered insignifi cant 

because of absence of thick shale units in the stratigraphic 

section. Loss of sedimentary section associated with late, midCretaceous and mid-Eocene erosional events was accounted 

for in the burial-history curves. 

Dutton (1987) provided justifi cation for using the average 

present-day geothermal gradient of 2.1°F/100 ft for the paleogeothermal gradient for the fi ve northernmost wells. Paleogeothermal gradients in the two southern wells probably were 

elevated temporarily because of proximity to the area of initial 

continental rifting. Based on the crustal extension model of 

Royden and others (1980), Dutton (1987) estimated values 

for elevated paleogeothermal gradients for these two wells for 

80 m.y. following the onset of rifting before reverting to the 

present-day gradient for the past 100 m.y.

Using estimated paleogeothermal gradients in conjunction with burial-history curves, Dutton (1987) found that calculated values of Ro for Travis Peak shales agree well with 

measured values. Because of this agreement, Dutton (1987) 

used the same method to calculate Ro values for tops of the 

Cotton Valley Group, Bossier Shale, and Smackover Forma16 Geologic Studies of Basin-Centered Gas Systems
tion in eastern Texas. Estimated Ro values for the Bossier Shale 

and Smackover in seven wells range from 1.8 to 3.1 percent 

and 2.2 to 4.0 percent, respectively, suggesting that these rocks 

have reached a stage of thermal maturity in which dry gas was 

generated. Assuming that high-quality, gas-prone source rocks 

occur within these two formations, it is likely that one or both 

of these units generated gas found in overlying Cotton Valley 

and Travis Peak reservoirs. 

No such regional source-rock and thermal-maturity analysis is known for Travis Peak and Cotton Valley intervals in 

northern Louisiana. Scardina (1981) presented burial-history 

data for the Cotton Valley Group, but included no information 

on geothermal gradients and thermal history of rock units. 

Present-day reservoir temperatures in tight Cotton Valley sandstones of eastern Texas and the tight, massive Terryville Sandstone in northern Louisiana both are in the 250°F to 270°F 

range (Finley, 1986; White and Garrett, 1992). It is likely 

that Bossier and Smackover source rocks in northern Louisiana experienced relatively similar thermal history to their 

stratigraphic counterparts in eastern Texas and, therefore, are 

sources for Cotton Valley gas in northern Louisiana. Herrmann 

and others (1991) presented a burial-history plot for Ruston 

fi eld in the Cotton Valley blanket-sandstone trend in northern 

Louisiana. They suggested that Smackover gas was derived 

locally from Smackover lime mudstones and Cotton Valley gas 

from Cotton Valley and Bossier shales. Their burial-history 

plot shows the onset of generation of gas from Smackover 

and Bossier source rocks at Ruston fi eld occurred about 80 

Ma and 45 Ma, respectively. As noted above in this report, 

the Sabine uplift has been a positive feature for the past 60 

m.y. (Kosters and others, 1989; Jackson and Laubach, 1991). 

Therefore, it would have been a focal area for gas migrating 

from Smackover, Bossier, and upper Cotton Valley source 

rocks in eastern Texas and northern Louisiana.

Abnormal Pressures

Pore pressure or reservoir pressure commonly is reported 

as a fl uid-pressure gradient (FPG) in pounds per square inch/

foot (psi/ft). Normal FPG is 0.43 psi/ft in freshwater reservoirs 

and 0.50 psi/ft in reservoirs with very saline waters (Spencer, 

1987). Abnormally high pore pressures as high as 0.86 psi/ft 

have been encountered in Cotton Valley reservoirs in northeastern Louisiana (fi g. 9). Multiple FPG values for a particular 

gas fi eld in fi gure 9 refer to gradients calculated for different, 

stacked blanket-sandstone reservoirs penetrated in that fi eld. 

Across northern Louisiana, as shown in fi gure 9, the highest 

FPG’s of 0.84 and 0.86 psi/ft occur in the southeast, and 

gradients generally decrease to nearly normal values of 0.43 

to 0.50 psi/ft in the northwest. This pattern exhibits general 

agreement with reservoir-pressure data for northern Louisiana 

summarized by Coleman and Coleman (1981) (fi g. 10). The 

dashed line in fi gure 10 shows a modifi cation of Coleman 

and Coleman’s (1981) pressure boundary to include the 0.63 

psi/ft gradient in Hico-Knowles fi eld and 0.67 psi/ft gradient 

in Tremont fi eld (fi g. 9). Most signifi cant for this study, 

the boundary between overpressured and normally pressured 

Cotton Valley sandstones (fi g. 10) shows no relationship to 

the two different productive Cotton Valley sandstone trends 

defi ned by differences in reservoir properties (fi g. 8). Additionally, most Cotton Valley sandstone reservoirs, especially in the 

tight, massive-sandstone trend across northwestern Louisiana 

and eastern Texas are normally pressured, as shown in fi gure 9.

History of Cotton Valley Group 

Sandstone Exploration

Beginning in 1937 and continuing through the early 

1960’s, commercial gas production was established from 

porous and permeable Cotton Valley Group blanket-sandstone 

reservoirs across northern Louisiana. Blanket sandstones 

fl owed gas at commercial rates without artifi cial stimulation. 

Initial discoveries were in anticlinal traps associated with salt 

structures. Subsequent discoveries came from more complex 

and subtle traps, including (1) combination traps with blanket 

sandstones pinching out across anticlines or structural noses, 

and (2) stratigraphic traps with blanket sandstones pinching 

out on regional dip (Pate, 1963; Coleman and Coleman, 1981). 

By the early 1960’s, the high-porosity blanket-sandstone play 

matured, and exploratory drilling waned. Low-porosity, lowpermeability, Cotton Valley massive sandstones to the south in 

Louisiana and to the west on the Sabine uplift in northwestern 

Louisiana and eastern Texas fl owed gas at rates less than 1,000 

MCFD (thousand cubic feet of gas per day) and were not commercial with gas selling at $0.18/MCF in the 1960’s (Collins, 

1980). 

In the 1970’s, gas production from low-permeability, 

Cotton Valley massive sandstones became commercial as a 

result of technical advances in hydraulic-fracturing techniques 

together with signifi cantly higher gas prices. At Bethany fi eld 

on the Sabine uplift in eastern Texas in 1972, Texaco successfully increased the rate of production from tight Cotton 

Valley sandstones from 500 MCFD to a sustained rate of 2,500 

MCFD and 30 BCPD (barrels of condensate per day) through 

hydraulic fracturing (Jennings and Sprawls, 1977). In conjunction with development of improved stimulation technology, 

price deregulation through the Natural Gas Policy Act (NGPA) 

of 1978 spawned a dramatic increase in drilling for gas in 

low-permeability Cotton Valley sandstones (Bruce and others, 

1992). In 1980, the Federal Energy Regulatory Commission 

(FERC) offi cially classifi ed low-permeability Cotton Valley 

sandstones as “tight gas sands,” qualifying them for additional 

price incentives. Production from tight Cotton Valley sandstones surged. At Carthage fi eld in eastern Texas, for example, 

production from Cotton Valley sandstones increased from 2.2 

BCFG (billion cubic feet of gas) in 1976 to 70.9 BCFG 

in 1980 (Meehan and Pennington, 1982). The large area 

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 17
CALHOUN

0.860.47

Cotton Valley Group sandstone fieldFluid-pressure gradient (psi/ft) fordifferent Cotton Valley sandstones

LEGEND

ARKANSAS

LOUISIANA

LOUISIANA

TEXAS

Dallas

Kaufman Gulf of Mexico

TX

LA

OK AR

DETAIL MS AL

AREA

LOCATION MAP

0 50 25

Miles

FLUID-PRESSURE GRADIENTS (PSI/FT)

COTTON VALLEY GROUP SANDSTONES

BENTON

0.470.44

S SAREPETA0.500.490.49

COTTON VALLEY0.550.510.490.43

HAYNESVILLE

0.43

ELM GROVE

0.53

BETHANY EAST

0.51

CARTHAGE

0.55

OAK HILL

0.32

SUGAR CREEK

0.450.34

HICO KNOWLES

0.630.470.42 RUSTON 0.47

CHENIERE

0.84

S DREW

0.530.45

TREMONT0.670.46

CALHOUN

0.860.47

Blanket-sands

trend

Figure 9. Map of northeastern Texas and northwestern Louisiana showing fl uid-pressure gradients calculated from shut-in pressures in Cotton Valley GroMultiple pressure-gradient values for a particular gas fi eld refer to gradients calculated for different, stacked blanket-sandstone reservoirs penetrated in tdata for Louisiana fi elds shown in table 2.
ARKANSAS

LOUISIANA

LOUISIANA

TEXAS

Dallas

Kaufman Gulf of Mexico

TX

LA

OK AR

DETAIL MS AL

AREA

LOCATION MAP

0 50 25

Miles

DISTRIBUTION OF RESERVOIR PRESSURES

COTTON VALLEY GROUP SANDSTONES

NORMALLY

OVERPRESSURED

Blanket sandsto

trend

PRESSURED

Figure 10. Map of northeastern Texas and northwestern Louisiana modifi ed from Coleman and Coleman (1981) showing geographic distribution of abnorm

Cotton Valley Group sandstone reservoirs. Dashed line shows modifi cation of Coleman and Coleman’s (1981) pressure boundary to include the 0.63 psi/ft fl uHico-Knowles fi eld and 0.67 psi/ft gradient in Tremont fi eld as shown in fi gure 9 and documented in table 2. Comparison of this map with map in fi gure 8 shooverpressure and normal pressure cuts across two productive trends of Cotton Valley sandstones.
across northern Louisiana and northeastern Texas within which 

Cotton Valley sandstones have been designated tight-gas sandstones by FERC includes all the counties identifi ed by name 

on fi gure 4 (Dutton and others, 1993).

Comparison of Blanket-Sandstone 

and Massive-Sandstone Trends

Two productive Cotton Valley sandstone trends are identifi ed based on reservoir properties (fi g. 8). As described above, 

Cotton Valley sandstone reservoir properties are a function 

of diagenetic characteristics, which are controlled primarily 

by variations in depositional environment. Reservoir properties, in turn, govern gas-production characteristics, including 

both initial rate of gas production and necessity of hydraulicfracture treatments to achieve commercial production rates. 

Table 1 summarizes these and other key parameters distinguishing blanket- and massive-sandstone Cotton Valley reservoir trends. Data presented in table 1 were derived from a 

variety of sources as indicated in the table headnote, with 

much of the information coming from a series of reports by 

the Shreveport Geological Society on oil and gas fi elds in 

northern Louisiana (Shreveport Geological Society Reference 

Reports, 1946, 1947, 1951, 1953, 1958, 1963, 1980, 1987). 

Detailed information obtained from those reports on more than 

20 Cotton Valley oil and gas fi elds in northern Louisiana, 

including data on porosity, permeability, initial production 

rates, gas-water contacts, and FPG’s, is presented in table 2.

Most of the signifi cant fi elds across northern Louisiana 

and northeastern Texas from which Cotton Valley sandstones 

produce gas are shown in fi gure 8. The area shown in fi gure 

8 is part of the larger region shown in fi gure 4 within which 

Cotton Valley sandstones were designated as tight-gas sandstones by FERC in 1980. As shown in fi gure 8, however, 

15 Cotton Valley fi elds were excluded from FERC’s tight-gas 

sandstone designation. All but one of these fi elds are located 

within the porous and permeable Cotton Valley blanketsandstone trend.

Blanket-Sandstone Trend

Transgressive, Cotton Valley blanket sandstones have 

porosities ranging from 10 to 19 percent and permeabilities 

from 1 to 280 mD (tables 1 and 2). Porosity and permeability 

data are not readily available for all productive blanket sandstones in Cotton Valley fi elds. However, suffi cient data are 

available from several blanket-sandstone reservoirs within a 

dozen fi elds across northern Louisiana to observe the widespread distribution of relatively high quality reservoir sandstones across the Cotton Valley blanket-sandstone trend (fi g. 

11). Data shown in fi gure 11 are derived primarily from fi eld 

reports by the Shreveport Geological Society and from White 

and others (1992). Multiple values of porosity and permeability for a given fi eld in fi gure 11 represent measured values 

for separate, stacked blanket-sandstone reservoirs within that 

fi eld. Average porosity and permeability for Cotton Valley 

blanket sandstones, calculated from data in fi gure 11, are 15 

percent and 110 mD, respectively. 

The relatively high porosity and permeability of blanket 

sandstones is refl ected in (1) the ability of these sandstones 

to fl ow gas and (or) liquids on open-hole DST’s, and (2) 

high initial fl ow rates of gas from these sandstones in production tests without hydraulic-fracture stimulation treatments, as 

shown in fi gure 12. Multiple values of initial fl ow rates for 

a given fi eld shown in fi gure 12 indicate rates from different 

stacked blanket sandstones that produce in that fi eld. Across 

Table 1. Comparison of two productive trends of Cotton Valley Group sandstones in eastern Texas and northern Louisiana. 

[Data from Shreveport Geological Society (1946, 1947, 1951, 1953, 1958, 1963, 1980, 1987); Collins (1980); Nangle and others (1982); Finley (1984, 1986); 

Bebout and others (1992); and Dutton and others (1993). TSTM, too small to measure] 

Parameter Blanket sandstone Massive sandstone 

Porosity (percent) 10 to 19 (average = 15) 6 to 10 

Permeability (mD) 1.0 to 280 (average = 110) 0.042 (E. Texas) 0.015 (N. Louisiana) 

Open-hole DST Wells flow gas and (or) liquids Wells generally do not flow gas or liquids 

Stimulation treatment No treatment necessary for commercial production Massive-hydraulic fracturing required to achieve 

commercial production 

Initial flow rates (MCFD) 500 to 25,000 (average 5,000) Pre-stimulation: TSTM to 300 

 Post-stimulation: 500 to 2,500 

Sw in productive zones < 0.40 Can be as high as 0.60 

Gas/water contacts Short, well-defined transition zones and gas-water 

contacts 

Long transition zones with poorly defined gas-water

contacts 

Formation damage Possible Commonly severe 

20 Geologic Studies of Basin-Centered Gas Systems
ARKANSAS

LOUISIANA

LOUISIANA

TEXAS

0 50 25

Miles

Cotton Valley Groupsandstone fieldPermeability (mD)

TREMONT14 34 Porosity

(percent)

LEGEND

POROSITY AND PERMEABILITY

COTTON VALLEY GROUP BLANKET SANDST

BENTON

1814

135

85

S SAREPETA

171312

265

7550

COTTON VALLEY

15

18

1616

280150121

34

LISBON

1714

150

40

LEATHERMAN

CREEK

12 1

TERRYVILLE

10 125

191818

NE LISBON

17 196 HICO KNOWLES

181715

CHOUDRANT

0.19 250

RUSTON

1715

CALHOUN 150 100

80

S DREW

1210

20

8

TREMONT

14 34

Blanket-sandstone trend

Figure 11. Map of northeastern Texas and northwestern Louisiana showing measured values of porosity and permeability in Cotton Valley Group blanket sa

and permeability data documented in table 2. Multiple values of porosity and permeability for a given fi eld represent measured values for separate, stacked reservoirs in that fi eld.
Table 2. Data on Cotton Valley Group sandstone fields in northern Louisiana. 

[See end of table for explanation of abbreviations] 

Field FERC Trend Trap Disc CV disc date: ss Depth CV perfs IP (CV) GOR Por Perm (mD) BHT BHP FPG Sw GWC 

 “tight” date (ft) (MCFD) (BOPD) (BCPD) (BWPD) (%) Avg Min Max (°F) (psi) (psi/ft)

Ada-Sibley Yes M Comb (FA, FC) 1936 1954: CV 9,900 Athens B Struct (FA) 1941 1948: Vaughn 8,500-8,544 10,500 254 41,338:1 

 or 

les No B 

1949: "B" 8,464-8,494 12,000 156 76,923:1 1950:Bodcaw 8,148-8,186 694 2 347,000:1 1951: "D" 8,145-8,170 3,370 208 16,201:1 

Bayou Middlefork Yes B Struct (A) 1953: Bodcaw 7,764 191 210 00,909:1Bear Creek-Bryceland Yes M Struct (A) 1937 1966 CV 10,700 Beekman No Comb (N, FC) 1942 1942: Cv 3,700-3,711 1,500 35 28 42,800:1 Benton Yes B Struct (A) 1944 1944: "D" 8,001-8,040 3,280 164 20,000:1 18 136 190 3,765 0.47 0.17 GWC -7,818 

1945: Bodcaw 8,137-8,148 1,306 127 10,286:1 14 85 190 3,725 0.44 OWC -7,876

Blackburn Yes B Comb (N, FC) 1953 1953: Bodcaw 8,717 1,301 54 24,092:1 E. Blackburn Yes B 1959

Cadeville Yes B 1955 9,700 Calhoun No B Struct (FA) 1948 1948: "D" 9,500 814 22 37,000:1 17 4,000 0.47  Comb (FA, FC) 1957: Cadeville 9,121-9,124 4,779 1,148 4,162:1 15 2,132 8,201 0.86 0.05 Carlton Yes B Struct (A) 1953 1953: BodcawN. Carlton No B Comb (A,FC) 1964: Purdy 8,950 

1965: CV ? 9,470

Cartwright Yes B 1960Caspiana Yes M Comb (N, FC) 1975: Cotton Valley 8,500 Cheniere No B Comb (N, FC) 1962 1962: Cadeville 9,682-9,697 4,401 528 8,335:1 8,188 0.84 

1963: CV "A" 9,603-9,609 1,230 8 153,750:1 

Choudrant Yes B Struct (A) 1946 1946: "D" 9,097--9129 4,732 211 21,000:1 19 250 Separate GWCs in 2 

Clay Yes M Struct (A) 1952: CV 9,700 Cotton Valley No B Struct (A) 1922 1937: Bodcaw 8,170 TD (OH) 5,323 455 11,700:1 16 121 775 231 4,000 0.49 0.15 GWC @ -8,420  1937: Davis 8,521-8,551 (OH) 4,800 400 12,000:1 15 280 4,368 0.51 0.10 

1938: "D" 8,502-8,532 1,020 1,200 00,850:1 18 150 3,926 0.43

 1949: Justiss 

C" 

9,050 16 34 4,700 0.55 0.22 

"Tayl

D'Arbonne Yes B 1947 1947: Bodcaw 8,157 4,100 88 46,590:1

Dixie Yes B 1929Downsville Yes B 1948S. Downsville No B Struct (A) 1961 1961: Vaughn 8,900 S. Drew Yes B Strat (FC) 1972 1972: "D" 9,061-9,069 2,560 85,000:1 12 20 200 4,850 0.53 0.40 3 GWCs in "D" ss  1976: Vaughn 9,525-9,531 873 15 58,200:1 10 8 200 4,250 0.45 0.40 

Elm Grove Yes M Struct (FA) 1973 Cotton Valley 7,768 8 1 247 4,154 0.53 0.45

Greenwood-Waskom No B 1924Haynesville Yes B Struct (A) 1921 1944: Taylor 8,835-8,920 373 01068:1 3,870 0.43 

1945: Camp 7,980-8,004 264 00500:1 

E. Haynesville Yes B 1945 1949: Tucker 8,588-8,600 2,898 276 10,500:1 Hico-Know

Hico No B Struct (FA) 1946 1946: Vaughn 8,525-8,556 8,240 121 68,100:1 17 3,686 0.42 Multiple GWCs 

1946: Bodcaw 8,287-8,345 892 41 21,649:1 18 4,061 0.47 1949: Feazel-McFearin 8,914-8,929 2,880 308 9,350:1 15 5,616 0.63

Knowles No B Struct (A) 1945 1945: Vaughn 8,700-8,750 5,212 139 37,500:1 3,500 0.40 

1946: Bodcaw 8,630-8,670 8,516 158 53,900:1 1948: McCrary 8,912-8,924 6,762 761 8,886:1 

 1953: Feasel-McFearin 8,996-9,008 7,000 275 25,450:1 
Field Name of field producing from Cotton Valley Group (CV) sandstone 

FERC “tight” Did FERC designate the field “tight-gas sand” for Cotton Valley Group?Trend B, Blanket-sandstone trend  M, Massive-sandstone trend Trap Trapping mechanism for field  Struct, structural trap  Strat, stratigraphic trap  Comb, combination structural & stratigraphic trap  A, anticline  FA, faulted anticline  FC, facies change (sandstone pinchout)  N, structural nose Disc date Discovery date of field CV disc date: ss Date of CV sandstone discovery and specific CV ss that was productive Depth CV perfs Depth in feet of CV perforations in discovery well for specific ss 

IP (CV) IP for specific CV ss GOR Gas:oil ratio Por Porosity (decimal) Perm Permeability (mD) [nonstressed] BHT Bottom hole temp (°F) BHP Bottom hole pressure (psi) FPG Fluid-pressure gradient (psi/ft) Sw Water saturation (decimal) GWC Information about gas-water contact Drive Drive mechanism  SG, solution gas  PD, pressure depletion  GC, Gas-cap expansion  WD, water drive SGS ref report Shreveport Geological Society Referen

Table 2. Data on Cotton Valley Group sandstone fields in northern Louisiana—Continued. 

Field FERC Trend Trap Disc CV disc date: ss Depth CV perfs IP (CV) GOR Por Perm (mD) BHT BHP FPG Sw GWC 

 “tight” date (ft) (MCFD) (BOPD) (BCPD) (BWPD) (%) Avg Min Max (°F) (psi) (psi/ft)

Homer Yes M 1919 Ivan Yes B 1952

Lake Bistineau Yes M 1916Leatherman Creek Yes M Struct (FA) 1975 1975: Cotton Valley 10,400-10,800 12 1 0.30 Lisbon No B Struct (FA) 1936 1939: Vaughn 8,444-8,464 5,000 61 82,000:1 17 150 0.35 

1940: Burgess-Simmons 8,766-8,806 1,993 160 12,458:1 14 40 

N. Lisbon No B Comb (N, FC) 1941 1942: Burgess-Simmons 8,502-8,525 510 17 30,000:1 

1943: Bodcaw 7,790-7,816 19,000 17 196 

Longwood Yes M Strat (FC) 1927 1948: Bodcaw 8,350 Minden Yes M 1957

Plain Dealing Yes M 1946Rocky Mount Yes B 1959Ruston No B Comb (A,FC) 1943 1948: "D" 8,796-8,806 6,500 56 24,000:1 18 100 210 4,100 0.47 0.23 GWC in Vaughn ss 

1949: Bodcaw 8,707-8,730 4,263 195 21,860:1 19 150 1949: Vaughn 8,809-8,838 7,995 390 20,501:1 1949: "D" 8,674-8,706 8,250 1949: Bodcaw 8,760-8,810 15,500 1951: Feazel (Davis) 9,468-9,476 1,062 50 21,240:1 18 80 

S. Sarepta Yes B Comb (FA,FC) 1949 1949: Bodcaw 8,710 2,160 173 12,485:1 17 265 4300 0.49 0.14  1949: Savis 9,000 13 75 4,500 0.50 0.15 

1949: Ardis 9,150 12 50 4,525 0.49 0.14 

Sentell No B Comb (N, FC) 1951 1951: Bodcaw 8,320 25,500 455 56,043:1 16 50 

Shongaloo Yes B 1921

Sligo No M 1922 Sugar Creek Yes B Struct (FA) 1930 1957: Bodcaw 8,724-8,730 5,000 210 23,810:1 3,972 0.45 

1957: Vaughn 8,780-8,795 2,850 48.5 58,763:1 2,955 0.34

1958: "D" 7,917-7,925 21,000 896 23,437:1 1962: "D" 7,686-7,693 3,200 112 28,571:1 1962: McFearin 8,003-8,008 2,800 168 17,500:1

1979: Price 9,462-9,474 520 

Terryville No B Comb (N, FC) 1954 1954: "D" 9,203-9,227 3,739 277 13,514:1 10 125 GWC in "D" ss 

1957: "C" 9,169-9,182 1,030 38 29 27,105:1 

1959: "C" 9,049-9,053 133 00,934:1 

1962: McGrary 9,354-9,362 4,000 300 13,333:1 

Tremont Yes B Comb (N, FC) 1944 1944: Bodcaw 9,060-9,080 2,235 97 23,000:1 4,200 0.46 

1971: Davis 9,633-9,706 1,145 144 7,951:1 14 34 217 6,519 0.67 0.15 

Unionville Yes B Strat (FC) 1950 1950: Vaughn 8,550 

1950: Davis 8,700 

Vernon Yes M Strat (FC) 1967: Cadeville 10,900 
the blanket-sandstone trend, as shown in fi gure 12, initial 

production rates range from 500 MCFD to 25,000 MCFD and 

average 5,000 MCFD. 

Gas-water contacts have been reported from seven fi elds 

across the blanket-sandstone trend as shown in fi gure 13. In 

Hico-Knowles, South Drew, and Choudrant fi elds, separate 

gas-water contacts for individual blanket-sandstone reservoirs 

have been identifi ed (table 2). No gas-water contacts were 

encountered in Cheniere fi eld as of 1963 or in Tremont fi eld 

as of 1980 (table 2). In all other Cotton Valley fi elds described 

in Reference Reports by the Shreveport Geological Society 

(1946, 1947, 1951, 1953, 1956, 1963, 1987), no mention of 

fl uid contacts was made. 

Massive-Sandstone Trend

Cotton Valley sandstones in the massive-sandstone trend 

(fi g. 8 and table 1) have signifi cantly poorer reservoir properties than those in the blanket-sandstone trend. Massive Cotton 

Valley sandstones have suffi ciently low permeability that they 

generally do not fl ow gas or liquids during open-hole DST’s, 

and they require fracture-stimulation treatment to obtain commercial rates of gas production (Collins, 1980). Commercial 

gas production from these sandstones was not achieved 

until technological advances in hydraulic fracturing occurred 

together with higher gas prices from deregulation in the 

1970’s. Consequently, development of Cotton Valley fi elds 

in the tight, Cotton Valley massive-sandstone trend did not 

occur until the late 1970’s and 1980’s. Cotton Valley development drilling in Elm Grove and Caspiana fi elds in northern 

Louisiana continues at the time this report is being written 

(Al Taylor, Nomad Geosciences, oral commun., April 2000). 

A consequence of such recent development of fi elds in the 

tight, Cotton Valley massive-sandstone trend is less published 

information on characteristics of these fi elds than on older 

fi elds in the blanket-sandstone trend.

Limited Data in Published Literature

Summary information presented by Dutton and others 

(1993) for the tight, Cotton Valley massive-sandstone trend 

across northeastern Texas and northern Louisiana indicates 

porosities in the 6- to 10-percent range. Based on measurements from cores in 11 wells in Carthage fi eld, one of the 

largest Cotton Valley fi elds in northeastern Texas, Wilson and 

Hensel (1984) reported porosities ranging from 5.8 to 8.1 

percent, with an average of 6.6 percent. Associated permeabilities range from 0.02 to 0.33 mD, with an average of 

0.067 mD. From core data for 126 wells in Harrison and Rusk 

counties in northeastern Texas, Finley (1984) reported an average permeability of 0.042 mD for Cotton Valley sandstones. 

In northern Louisiana, average permeability was reported as 

0.015 mD based on data from Cotton Valley cores in 302 

wells. However, there are stratigraphic intervals within the 

tight, Cotton Valley massive-sandstone trend with signifi cantly 

higher permeabilities. Locally, permeabilities approaching 100 

mD have been reported (Wilson and Hensel, 1984). 

Signifi cantly lower porosity and permeability of tight, 

Cotton Valley massive sandstones relative to blanket sandstones is refl ected in poorer production characteristics. The 

average fl ow rate prior to fracture-stimulation treatment is 

50 MCFD (Dutton and others, 1993). Post-stimulation rates 

generally are in the 500 to 2,500 MCFD range, although 

rates as high as 10,000 MCFD and 11,700 MCFD have been 

reported from Bethany fi eld (Jennings and Sprawls, 1977) and 

Carthage fi eld (Meehan and Pennington, 1982), respectively. 

There are few published data on presence of gas-water 

contacts or production of water without gas on the fl anks 

of Cotton Valley fi elds in the tight, massive-sandstone trend. 

Summary data presented by Nangle and others (1982) 

described gas-water contacts as poorly defi ned with long transition zones in contrast to short, well-defi ned transition zones 

with sharp gas-water contacts in the blanket-sandstone trend. 

Dutton and others (1993) also suggested the presence of gaswater contacts with long transition zones by indicating that 

calculated water saturations should be less than 40 percent to 

achieve successful gas completions from Cotton Valley sandstone intervals 200 ft above the free-water level. 

In northeastern Texas, where most of the drilling for 

tight Cotton Valley sandstones has occurred, the best reservoir 

potential is reported to be in wave-dominated deltaic sandstones of the Taylor sandstone in the lower part of the Cotton 

Valley interval (Wescott, 1983, 1985). In Oak Hill fi eld, production logs show that Taylor sandstones contribute more than 

80 percent of the gas production and that sandstones in the 

middle and upper Cotton Valley section contribute most of 

the water production, although they produce signifi cant gas 

as well (Tindall and others, 1981). Presley and Reed (1984) 

and Dutton and others (1993) both report the presence of 

water-bearing sandstones in the upper Cotton Valley interval. 

To avoid production of water from these sandstones, fracturestimulation treatments in stratigraphically adjacent gas-bearing 

sandstones in the upper Cotton Valley must be signifi cantly 

smaller than those in the Taylor sandstone. At Bethany fi eld, 

several wells reportedly were plugged because of production 

of salt water from Cotton Valley sandstones (Jennings and 

Sprawls, 1997).

Analysis of Drill-Stem-Test 

and Production-Test Data

As mentioned above, general statements in published 

reports suggest the presence of gas-water contacts in fi elds 

that produce gas from tight Cotton Valley sandstones across 

northeastern Texas and northern Louisiana. Unlike data for the 

Cotton Valley blanket-sandstone trend, however, no documentation was found identifying specifi c gas-water contacts in Cotton 

Valley sandstones in any of the tight-gas-sandstone fi elds in 

Texas or Louisiana. In the absence of such published data, and 

24 Geologic Studies of Basin-Centered Gas Systems
ARKANSAS

LOUISIANA

LOUISIANA

TEXAS

Dallas

Kaufman Gulf of Mexico

TX

LA

OK AR

DETAIL MS AL

AREA

LOCATION MAP

0 50 25

Miles

Cotton Valley sandstone fieldInitial rates of gas production (MCFD) from differentCotton Valley sandstones without fracture stimulation

BENTON

3,2801,306

LEGEND

INITIAL RATES OF GAS PRODUCTION

COTTON VALLEY GROUP BLANKET SANDSTON

S SAREPETA

2,160

BENTON

3,2801,306

SENTELL

25,500

COTTON

VALLEY

5,3234,9001,020

BLACKBURN

1,301

E HAYNESVILLE

2,898

LISBON

5,0001,993

ATHENS

12,00010,500

3,370

694

SUGAR

CREEK

21,000

5,0003,2002,8502,800

520

TERRYVILLE

4,0003,7391,030

TREMONT

2,2351,145

CALHOUN

4,779

814

CHENIERE

4,4011,230

NE LISBON

19,000

510

HICO KNOWLES

8,5167,0006,7625,2122,880

RUSTON

15,500

8,2507,9956,5004,2631,062

CHOUDRANT

4,732

S DREW

2,650

873

Blanket-sandstone

trend

Figure 12. Map of northeastern Texas and northwestern Louisiana showing initial rates of gas production from Cotton Valley Group blanket sandstones. Mu

fl ow rates for a given fi eld represent rates from different stacked blanket-sandstone reservoirs that produce in that fi eld. All rates are from blanket sandstofracture-stimulation treatment for commercial production. 
ARKANSAS

LOUISIANA

LOUISIANA

TEXAS

Dallas

Kaufman Gulf of Mexico

TX

LA

OK AR

DETAIL MS AL

AREA

LOCATION MAP

0 50 25

Miles

KNOWN FIELDS WITH GAS-WATER CONTACT

 IN COTTON VALLEY GROUP SANDSTONES

BENTON

COTTON

VALLEY HICO

KNOWLES

TERRYVILLE

RUSTON

CHOUDRANT

S DREW

Blanket-sands

trend

Figure 13. Map of northeastern Texas and northwestern Louisiana showing fi elds productive from Cotton Valley Group sandstones in which gas-water con

identifi ed and reported in published literature. Presence of gas-water contacts in these fi elds suggests that they are conventional gas accumulations. Detacontacts, including sources of information, are shown in table 2.
considering the diffi culties of using wireline logs to evaluate 

water saturations in tight Cotton Valley sandstones, an attempt 

was made to document the presence or absence of gas-water 

contacts through analysis of data from DST’s and production 

tests. The goal was to determine if Cotton Valley fi elds that 

produce from tight-gas sandstones are fl anked by dry holes that 

tested water without gas, suggesting presence of a gas-water 

contact. A data set of wells penetrating the Cotton Valley Group 

across most of northeastern Texas and northern Louisiana was 

extracted from a database (PI/Dwights Plus, a trademark of 

Petroleum Information/Dwights, d.b.a. IHS Energy Group) for 

analysis of DST and production-test data using ArcView software. Because tight Cotton Valley sandstones generally do not 

fl ow fl uids on open-hole DST’s, it was anticipated that the 

most useful data would be derived from production tests made 

through perforations in casing following fracture-stimulation 

treatments. Well data were sorted and displayed in map view 

using ArcView software such that wells that produce from 

Cotton Valley sandstones could be distinguished from dry holes 

with tests. While viewing the map display, test results from any 

particular well could be examined. 

Reconnaissance analysis of data from Carthage, Bethany, 

Oak Hill, Waskom, and Woodlawn fi elds in northeastern Texas 

and from Bear Creek–Bryceland, Elm Grove, and Caspiana 

fi elds in northern Louisiana revealed few dry holes penetrating 

Cotton Valley strata on the fl anks of these Cotton Valley fi elds. 

No fl anking dry holes were found that tested only water. The 

few Cotton Valley dry holes present generally did not report 

tests, suggesting that no tests were performed in those wells 

and that, most likely, the wells were plugged based on evaluation of wireline logs. 

Test results from Cotton Valley sandstones in Oak Hill 

fi eld in Texas and Elm Grove–Caspiana fi elds in Louisiana 

were evaluated more rigorously, revealing several general patterns. Initial rates of gas production generally are higher in 

crestal wells than in fl ank wells in these fi elds, as shown 

for Caspiana fi eld in fi gure 14. At both Oak Hill and Elm 

Grove–Caspiana fi elds, initial rates of gas production from 

Cotton Valley sandstones range from 1,000 to more than 4,000 

MCFD in central parts of the fi elds and generally are less than 

1,000 MCFD in structurally lower wells on edges of the fi elds. 

Many fl ank wells exhibit initial rates of less than 500 MCFD, 

as shown in fi gure 14. This trend exhibits more variability at 

Oak Hill fi eld, where a larger number of low-rate wells occur 

in the center of the fi eld. Such low-rate wells in the central 

part of the fi eld could be attributed to a number of factors, 

including reservoir variability, formation damage during drilling, and poor fracture-stimulation treatments. All these wells 

must be fracture stimulated, and signifi cant variation in success of such stimulation treatments is not uncommon. Also, 

initial rates on the western fl ank of Oak Hill fi eld are high 

and show an abrupt change to dry holes rather than a gradual 

decline toward the fl ank of the fi eld. One well there fl owed 

gas with an initial rate exceeding 4,000 MCFD and is fl anked 

to the west by four Cotton Valley dry holes. In three of 

these dry holes, Cotton Valley sandstones apparently were 

not tested, and a test in the fourth well must have resulted 

in noncommercial production with only “one unit of gas” 

reported. 

Initial rates of water production in BWPD (barrels of 

water per day) also were mapped at Oak Hill and Elm Grove–

Caspiana fi elds and show no obvious patterns across these 

fi elds. No attempt was made to contour water production data 

for several reasons. Not only is variability in initial rate of 

water production high and seemingly random, but also, data 

are incomplete. Whereas the IHS Energy database reports initial rate of gas production for most all wells in these fi elds, 

initial rate of water production is not reported for a signifi cant 

percentage of wells. In wells at Oak Hill or Elm Grove–

Caspiana fi elds, for which a value is entered in the appropriate 

position of the database for water production, a null value is 

never reported. Some volume of water production seems to 

occur along with gas in all these wells. Hence, it does not seem 

appropriate to interpret absence of water-production data for a 

given well as meaning zero production of water. Absence of 

data on initial water production is more prevalent for Oak Hill 

fi eld, and that factor alone makes it diffi cult to analyze water 

production from that fi eld. Data on initial water production 

at Elm Grove–Caspiana fi elds are more complete. Although 

initial rates of water production were considerably higher at 

Caspiana fi eld, data were more complete for that fi eld, and patterns of initial water production at Caspiana fi eld were evaluated by plotting barrels of water produced per MMCFG (bbl 

water/MMCFG). As shown in fi gure 15, wells in the central 

part of Caspiana fi eld commonly exhibit production of 100 or 

fewer bbl water/MMCFG. Progressing outward toward fl anks 

of the fi eld, rates of initial water production increase to 300 

bbl water/MMCFG and eventually to more than 600 bbl water/

MMCFG. The highest initial rate of water production occurs 

in a well on the western fl ank of the fi eld where production 

of 1,477 bbl water/MMCFG is reported (fi g. 15). That same 

well had an initial rate of gas production of only 325 MMCFD, 

as shown in fi gure 14. Nevertheless, no wells that tested water 

only without gas from Cotton Valley sandstones were identifi ed on the fl anks of Caspiana fi eld to suggest the presence of 

a gas-water contact for the fi eld. Twenty-one Cotton Valley dry 

holes were identifi ed surrounding Elm Grove–Caspiana fi elds. 

Of these, 19 wells reported no tests in the Cotton Valley sandstone interval, presumably indicating that no Cotton Valley 

tests were run and that Cotton Valley completions were made 

on the basis of wireline-log evaluation. Production tests after 

fracture-stimulation were run in two other wells. One reported 

“one unit of gas and one unit of oil,” presumably indicating 

noncommercial rates. The other well reported only “one unit of 

water,” suggesting that the Cotton Valley sandstone might be 

below a gas-water contact at that location. On the southern and 

western fl anks of Oak Hill fi eld, six Cotton Valley dry holes 

without tests were identifi ed, again suggesting abandonment 

of Cotton Valley potential based on wireline-log evaluation. 

Production tests were run in Cotton Valley sandstones in two 

wells on the western fl ank of Oak Hill fi eld. One reported “one 

unit of gas,” the other “one unit of gas and one unit of water.” 

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 27
R 13 W R 12 W

T 15 NT 14 N

583

250

1081

666

200 1587

980 2100 264

1350

3100 730

1250 548

938 1736 905 400 700

605

800 1 561

1512

1464

1800

1908

900 325

1450

1304

1200

1439

1250

1410

900

1300

2618

2723

2110

2232

1 unit gas 1 unit gas

1850

1170 1020

2108

860 1454

2000

2061

3230

2014 950

2500 1250

980

4850 2883

1591

1776

1800

1150

1750 1832

1687 1725

2376

2667 3050

1500

1500

956 185 1200

2006

2006

927

925

200 762

1700

1117

1035

1592

2256

1400

No Cotton Valley tests No Cotton Valley tests

2450 482

2500

2900

2100

2041

2022

500

150

785

583

250

1081

666

200 1587

980 2100 264

1350

3100 730

1250 548

938 1736 905 400 700

605

800 1 561

1512

1464

1800

1908

900 325

1450

1304

1200

1439

1250

1410

900

1300

2618

2723

2110

2232

1 unit gas

1850

1170 1020

2108

860 1454

2000

2061

3230

2014

950

2500 1250

980

4850 2883

1591

1776

1800

1150

1750 1832

1687 1725

2376

2667 3050

1500

1500

956 185 1200

2006

2006

927

925

200 762

1700

1117

1035

1592

2256

1400

TD Cotton Valley Gp.

No Cotton Valley Gp. tests

2450 482

2500

2900

2100

2041

2022

500

150

785

2000

1000

2000

4000 2000

1000

2000

1000

2000

1000

3000

1000

2000

1000

3000

1000

1000

1000

1000

2000

2000

3000

Figure 14. Map of Caspiana fi eld in northwestern Louisiana in the tight, Cotton Valley Group massive-sandstone trend showing initial rate of gas productioValley sandstone reservoirs. Data from PI/Dwights Plus, a trademark of Petroleum Information/Dwights, d.b.a. IHS Energy Group. Contour interval is 1,000 Mdecrease in initial rates of gas production from center to fl anks of fi eld. 
Figure 15. Map of Caspiana fi eld in northwestern Louisiana in the tight, Cotton Valley Group massive-sandstone trend showing ratio of initial production rat

production rate of gas (MMCFGD) from Cotton Valley Group sandstones. Data from PI/Dwights Plus, a trademark of Petroleum Information/Dwights, d.b.a. IHinterval is 100 BWPD/MMCFGD. Mapped data show progressive increase in ratio of initial production rates of water to gas from crest to fl anks of fi eld. This ssandstones, gas saturation is decreasing and water saturation is increasing from crest to fl anks of fi eld and indicates presence of vertically extensive gas-w

R 13 W R 12 W

T 15 N

T 14 N

E

600

500 400

300 300

400

500

600

700

800

500400

600 500

600

1000

500 400

300 200

100

100

200

200

600400

100

200

200 300

300200

100

400

400

300

300

200

100

100 200 300 400

500

600 500

400300 200 500

200

300

?

?

?

?

? ?

367

177 205 83

25

?

?

363 240 244 270 144 187

?

609

290

278

285

695 100

?

? ? ?

160

105 75 74

293 205

229

214

73 255

199

223 ?

33

38

95

207

377

398

178,000

694

344

1477 200

241

238

334

368

443

36 units wtr

1 unit gas

18 71

73

?

?

424

303 172

270 114

470

?

114

162 217

138 286

236 571 483

72

188

155

350

260

201

334

385

627

549

378

800

432

549

267
On the southern fl ank of the fi eld, production tests were run 

in Cotton Valley sandstones in two Cotton Valley dry holes, 

but no results were reported. Evaluation of test data from Oak 

Hill and Elm Grove–Caspiana fi elds, therefore, provides no 

defi nitive information regarding presence or absence of gaswater contacts in these Cotton Valley fi elds. 

Discussion of Evidence For 

and Against Basin-Centered Gas

Source Rocks and Burial and Thermal History

Source rocks responsible for generating gas in basincentered gas accumulations commonly are in stratigraphic 

proximity to low-permeability reservoirs that they are charging 

with gas. As described above, there are few published data on 

source rocks responsible for generating gas found in Cotton 

Valley sandstone reservoirs in both the blanket- and massivesandstone trends. However, the marine Bossier Shale, stratigraphically directly beneath Cotton Valley sandstones, and 

Smackover laminated lime mudstones, lying below the Bossier 

Shale, are considered to be source rocks capable of generating 

gas for Cotton Valley sandstone reservoirs. Gray to black 

marine shales interbedded with Cotton Valley sandstones also 

are considered to be potential source rocks. Also, as summarized above, burial- and thermal-history data for the northern 

Gulf Coast Basin suggest that burial depths of Bossier and 

Smackover source rocks, in conjunction with the regional geothermal gradient, have been suffi cient to generate dry gas. Time 

of generation of much of the gas postdates development of both 

the Sabine uplift and structures in the East Texas and Louisiana 

Salt Basins. Hence, available data on presence of source rocks, 

burial and thermal history of source rocks, and timing of gas 

generation for Cotton Valley reservoirs would be consistent 

with interpretation of a potential continuous gas accumulation 

in massive sandstones of the Cotton Valley Group.

Porosity, Permeability, 

and Gas-Production Rates

Basin-centered gas accumulations commonly involve 

large volumes of gas-saturated rock in which gas cuts across 

stratigraphic units. Such gas accumulations require a regional 

seal to trap gas, and that seal characteristically is provided by 

inherent low permeability of reservoir rocks themselves. Thus, 

continuous gas reservoirs characteristically have low permeability, and when reservoirs are sandstones, they commonly are 

referred to as tight-gas sandstones. 

As described above, Cotton Valley sandstone reservoirs 

across the northern Gulf of Mexico Basin can be divided into 

two groups based on reservoir properties and associated rates 

of gas production. Sandstones in the Cotton Valley blanketsandstone trend across northernmost Louisiana have porosities 

in the 10 to 19 percent range and permeabilities from 1 to 280 

mD (table 1). These sandstones generally fl ow gas and (or) 

liquids during open-hole DST’s. Gas-productive sandstones 

fl ow at initial rates ranging from 500 to 25,000 MCFD without 

fracture-stimulation treatment. Consequently, these sandstones 

are not tight-gas reservoirs, and many fi elds producing from 

Cotton Valley sandstones in the blanket-sandstone trend were 

excluded from tight-gas status by FERC in 1980 (fi g. 8). 

Therefore, in the absence of some other regional top seal that 

could allow development of basin-wide overpressure, sandstones in this trend would not be expected to host a basincentered gas accumulation. 

South of the blanket-sandstone trend in northern Louisiana lies the Cotton Valley massive-sandstone trend that extends 

westward across the Sabine uplift into northeastern Texas, as 

shown in fi gure 8. Cotton Valley massive sandstones generally 

have porosities in the 6 to 10 percent range with permeabilities 

commonly less than 0.1 mD. Most of these sandstones, therefore, would be defi ned as tight-gas sandstones, and most fi elds 

producing gas from these sandstones were designated as tightgas-sandstone fi elds by FERC in 1980. Tight, Cotton Valley 

massive sandstones generally do not fl ow gas and (or) liquids 

on open-hole DST’s, and they require hydraulic-fracture treatment to produce gas at commercial rates. As shown in table 

1, prestimulation initial-production rates generally range from 

too small to measure (TSTM) to 300 MCFD. Post-stimulation 

rates commonly are 500 to 2,500 MCFD. Although higher permeability intervals occur locally within the massive-sandstone 

trend, as noted by Wilson and Hensel (1984), the characteristic 

low permeability of sandstones throughout this trend suggests 

that they might have potential to provide their own seal for gas 

in a continuous gas accumulation.

Abnormal Pressures

In a study of abnormally high pressures in basin-centered 

gas accumulations in Rocky Mountain basins, Spencer (1987) 

considered reservoirs to be signifi cantly overpressured if 

FPG’s exceed 0.50 psi/ft where waters are fresh to moderately 

saline, and 0.55 psi/ft where waters are very saline. With 

formation-water salinity of Cotton Valley sandstone reservoirs 

on the order of 170,000 ppm TDS (Dutton and others, 1993), 

salinity is considered high, and reservoirs should be considered 

to be overpressured if their FPG’s exceed 0.55 psi/ft.

Based on Spencer’s (1987) cutoff value of 0.55 psi/ft, 

abnormally high reservoir pressures have been encountered in 

Cotton Valley sandstones in an area of northeastern Louisiana, 

shown in fi gure 10, where calculated pressure gradients of 0.63 

to 0.86 psi/ft occur. The boundary between areas of overpressure and normal pressure cuts across the permeable, blanketand tight, massive-sandstone trends such that overpressures 

occur within both reservoir trends. (fi gs. 8 and 10). Although 

overpressures associated with generation of gas might be antic30 Geologic Studies of Basin-Centered Gas Systems
ipated in tight Cotton Valley sandstones, such overpressures 

would not be expected to develop in high-permeability blanket 

sandstones without a subregional top seal stratigraphically 

above the sandstones. As shown in fi gure 9 and table 2, some 

of the separate, stacked blanket sandstones within Hico, Tremont, and Calhoun fi elds are overpressured, whereas others are 

normally pressured. Examination of discovery dates of gas 

in individual sandstones shows that, in all cases for these 

three fi elds, normally pressured sandstone reservoirs were discovered prior to overpressured ones. Thus, pressure differences among individual blanket-sandstone reservoirs indicate 

presence of separate, compartmentalized reservoirs rather than 

pressure depletion from production of gas from different sandstones that are in pressure communication. Additionally, normally pressured Cotton Valley sandstones were encountered at 

South Drew fi eld, whereas, at Cheniere fi eld immediately to 

the west, Cotton Valley sandstones were signifi cantly overpressured with an FPG of 0.86 psi/ft. Thus, for gas fi elds in 

the blanket-sandstone trend where data are abundant, reservoir 

pressures exhibit signifi cant variation from normal to abnormally high among separate sandstone reservoirs within individual gas fi elds and also between adjacent fi elds. Such compartmentalization of overpressured reservoirs in proximity to 

normally pressured ones, rather than development of overpressure on a regional scale, is more indicative of conventional gas 

fi elds than basin-centered gas accumulations. 

Within the western half of the blanket-sandstone trend 

and spanning the vast majority of the tight, massive-sandstone 

trend across northwestern Louisiana and northeastern Texas, 

FPG’s range from 0.32 to 0.55 psi/ft and, therefore, would be 

considered normal, according to the methodology of Spencer 

(1987). However, two episodes of erosion have occurred in 

northeastern Texas, one in late mid-Cretaceous time and the 

second in early mid-Tertiary time (Dutton, 1987; Laubach and 

Jackson, 1990; Jackson and Laubach, 1991). During late midCretaceous time, maximum erosion occurred on the crest of 

the Sabine uplift where approximately 1,800 ft of sedimentary 

section were removed. Tertiary erosion resulted in removal of 

about 1,500 ft of section across much of northeastern Texas. 

Burial-history data for the Ruston fi eld area in northern Louisiana on the boundary between overpressured and normally 

pressured regions, show about 1,500 and 500 ft of uplift and 

loss of section, respectively, in two erosional periods (Herrmann and others, 1991). It is possible, therefore, that, with 

deeper burial, reservoir pressures in much or all of the massive-sandstone trend could have been higher and that pressure 

reduction has occurred as a result of uplift and erosion. However, some of the gas found in Cotton Valley sandstone reservoirs could have been derived from Bossier Shale source 

rocks. Migration of most of that gas into Cotton Valley sandstones probably commenced between 57 and 45 Ma (Dutton, 

1987; Hermann and others, 1991). Therefore, if basin-wide 

overpressure in Cotton Valley sandstones were to have developed in response to thermal generation of gas from Bossier 

Shale source rocks, its development would have postdated both 

the Cretaceous and Tertiary erosional events.

The sharp boundary between overpressured and normally 

pressured areas of Cotton Valley sandstones (fi g. 10) and presence of overpressure in both permeable, blanket-sandstone 

and tight, massive-sandstone trends, suggest that abnormally 

high pressures encountered in Cotton Valley sandstones in 

northeastern Louisiana are not caused by thermal generation 

and migration of gas. Coleman and Coleman (1981) attributed 

development of overpressures in Cotton Valley sandstones 

across the region shown in fi gure 10 to a late stage of diagenesis in which extreme pressure, presumably overburden pressure, and temperature caused dissolution of silica at contact 

points of quartz-sand grains and precipitation of silica in adjacent pores. With pore waters apparently unable to escape, 

porosity reduction associated with this late-stage chemical 

compaction reportedly resulted in development of overpressure 

in Cotton Valley sandstones across the area shown in fi gure 

10. According to Coleman and Coleman (1981), a signifi cant 

factor in preventing fl uid loss from Cotton Valley sandstones 

during this late diagenetic episode was presence of a tight top 

seal provided by the Knowles Limestone and upper Cotton 

Valley–lower Hosston shales. 

If late-stage chemical compaction and cementation in 

conjunction with a top seal of tight limestone and shale are 

responsible for development of overpressure, it is not clear 

why the geographic distribution of overpressure exhibits the 

pattern shown in fi gure 10. Perhaps an alternative mechanism 

for generating the distribution of overpressures within Cotton 

Valley sandstones shown in fi gure 10 could be one reported 

by Parker (1972) as the cause for overpressures in Jurassic 

Smackover sandstone and carbonate reservoirs to the east in 

Mississippi. Parker (1972) noted that much of the Smackover 

gas is sour and has a relatively high content of CO2 and 

(or) N2. He suggested that migration of gases derived from 

Late Cretaceous emplacement of the Jackson (igneous) dome 

(fi g. 2) might be responsible for “infl ation” of pressures in 

well-sealed Smackover reservoirs. Specifi cally, Jones (1977) 

suggested that H2S and CO2 present in Smackover gas 

in Mississippi were derived from Smackover anhydrite and 

limestone/dolomite, respectively, which had been subjected 

to magmatic intrusion. The mapped pattern of overpressured 

Cotton Valley sandstones (fi g. 10) extends east-southeastward 

into Mississippi directly toward the location of Jackson dome 

(fi g. 2) (Studlick and others, 1990). Evidence supporting such 

a mechanism of overpressure development in Cotton Valley 

sandstones of northeastern Louisiana would be documentation 

of elevated levels of CO2 and (or) N2 in overpressured Cotton 

Valley sandstone reservoirs.

In summary, within most of the tight, Cotton Valley 

massive-sandstone trend across northwestern Louisiana and 

northeastern Texas, Cotton Valley reservoirs are slightly, but 

not signifi cantly, overpressured. Based on the methodology and 

terminology of Spencer (1987), these reservoirs would be characterized as normally pressured. Basin-centered, continuous 

gas accumulations commonly are signifi cantly overpressured. 

Although pressure data for the tight, Cotton Valley massivesandstone trend are not defi nitive, they tend to suggest that a 

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 31
basin-centered gas accumulation characterized by abnormally 

high pressures from geologically recent to present-day thermal 

generation of gas does not occur within Cotton Valley sandstone 

reservoirs.

Gas-Water Contacts

Perhaps the most defi nitive criterion for establishing the 

presence of a continuous gas accumulation is absence of gaswater contacts. Gas-water contacts are distinctive features of 

conventional gas accumulations. Presence of a gas-water contact indicates a change from gas-saturated to water-saturated 

porosity within a particular reservoir unit. This implies that a 

well drilled into that reservoir structurally below the gas-water 

contact should encounter only water, thereby demonstrating 

the absence of a continuous gas accumulation in that immediate area.

Within the blanket-sandstone trend across northernmost 

Louisiana, gas-water contacts have been reported in seven 

fi elds, as shown in fi gure 13. Because of relatively high 

porosity and permeability in blanket sandstones, gas-water 

contacts are sharp and often are reported as depth below 

sea level to the nearest foot. Separate gas-water contacts for 

individual, stacked blanket sandstones have been identifi ed 

in Hico-Knowles, South Drew, and Choudrant fi elds (table 

2). The seven fi elds in which gas-water contacts have been 

described are distributed across the blanket-sandstone trend 

(fi gure 13). Because of the relatively uniform distribution 

of high-permeability Cotton Valley sandstone reservoirs with 

conventional shale seals in fi elds across the blanket-sandstone 

trend, it is likely that all Cotton Valley fi elds in this trend have 

well-defi ned gas-water contacts similar to those documented in 

the seven fi elds shown in fi gure 13. The Cotton Valley blanketsandstone trend was defi ned as a continuous gas accumulation 

in the 1995 National Assessment of United States Oil and Gas 

Resources by the USGS (Schenk and Viger, 1996). However, 

the presence of abundant gas-water contacts across this area 

suggests that the blanket-sandstone trend should be redefi ned 

as a conventional gas play.

Evaluating the presence or absence of gas-water contacts 

in the tight, Cotton Valley massive-sandstone trend is more 

diffi cult. No reference to specifi c gas-water contacts for Cotton 

Valley massive sandstones in any Cotton Valley gas fi eld has 

been found in the published literature. Nangle and others 

(1982) and Dutton and others (1993), however, make general 

statements indicating that gas-water contacts are present in 

Cotton Valley fi elds across the tight, Cotton Valley massivesandstone trend. 

Although Taylor sandstones in the lower part of the 

Cotton Valley section produce gas in all signifi cant Cotton 

Valley fi elds in the tight, massive-sandstone trend, waterbearing sandstones have been reported along with gas-charged 

sandstones in the middle and upper Cotton Valley interval in 

some fi elds. The seal for gas in wave-dominated deltaic Taylor 

sandstones at Waskom fi eld reportedly is provided by marsh 

and lagoonal shales (CER Corporation and S.A. Holditch & 

Associates, 1991). This seal would be considered conventional 

rather than one provided by the low permeability of the reservoir sandstones. Along with Taylor sandstones, most of the 

upper Cotton Valley sandstone interval produces gas at some 

fi elds, such as Carthage fi eld, according to Al Brake (BP, 

oral commun., 2000). At other fi elds, such as Woodlawn and 

Blocker, however, gas is produced only from lower Cotton 

Valley Taylor sandstones and from a few sandstones in the 

uppermost Cotton Valley section. Intervening middle and 

upper Cotton Valley sandstones are reportedly water-bearing. 

The presence of individual gas-bearing and water-bearing 

sandstone intervals, separated by conventional shale seals, suggests the presence of gas-water contacts and is more indicative 

of conventional gas accumulations than of continuous gas 

accumulations. 

The complex diagenetic mineralogy of tight Cotton Valley 

sandstones probably precludes use of wireline logs to identify 

gas-water contacts. As reported above, complex diagenetic 

mineralogy of tight Cotton Valley sandstones dramatically 

affects values of resistivity and porosity measured by wireline 

logs and, hence, the determination of water saturation by standard calculation techniques. Because of vertical and lateral 

diagenetic variations, accurate determination of water saturation is diffi cult without accompanying lithologic data from 

cores or cuttings to calibrate wireline logs. Examination of 

production-test data from wells fl anking many Cotton Valley 

gas fi elds in the tight-gas-sandstone trend reveals no dry holes 

that tested water without gas. Therefore, even if wireline 

logs provided accurate estimates of water saturations in tight 

Cotton Valley sandstones, few wells apparently exist in which 

logs could be used to identify gas-water contacts. 

Reconnaissance evaluation of DST and production-test 

data from Cotton Valley sandstones in a number of fi elds in 

the tight-gas-sandstone trend revealed few dry holes penetrating Cotton Valley sandstones on fl anks of those fi elds. No 

dry holes were found that tested water without gas, thereby 

implying existence of a gas-water contact for a particular fi eld. 

Likewise, detailed examination of test data from all wells 

within and fl anking Oak Hill and Elm Grove–Caspiana fi elds 

in the tight-gas-sandstone trend revealed no fl ank dry holes 

that tested water without gas.

Initial rates of gas production from wells on the fl anks 

of Cotton Valley fi elds in the tight-gas, massive-sandstone 

trend, however, generally are lower than from crestal wells, as 

illustrated for Caspiana fi eld in fi gure 14. Also, as shown for 

Caspiana fi eld in fi gure 15, the ratio of initial rate of water production to initial rate of gas production in terms of bbl water/

MMCFG is signifi cantly higher in fl ank wells. Initial rates of 

gas production from crestal wells commonly range from 1,000 

to more than 4,000 MCFD and the ratio of initial rate of water 

to gas generally is less than 200 bbl water/MMCFG and often 

below 100 bbl water/MMCFG (fi gs. 14 and 15). Initial rates 

of gas production from fl ank wells generally are less than 

1,000 MCFD, and water production initially is signifi cantly 

higher, usually in the 300 to 600 bbl water/MMCFG range, 

32 Geologic Studies of Basin-Centered Gas Systems
but sometimes exceeding 1,000 bbl water/MMCFG (fi gs. 14 

and 15). These data suggest a decrease in gas saturation and 

an accompanying increase in water saturation in Cotton Valley 

sandstones from crestal wells to fl ank wells and that a commercial limit to gas production has been reached, although 

gas-water contacts have not been encountered.

Corroborating these suggestions from fi gures 14 and 15 

and data reported by Nangle and others (1982) is the experience 

of Al Taylor (Nomad Geosciences, oral commun., 2000) who 

reports the presence of vertically extensive gas-water transition 

zones in Cotton Valley sandstone fi elds in the massive-sandstone 

trend. In moving structurally lower from the crest of one of 

these tight-gas Cotton Valley fi elds through the long gas-water 

transition zone toward the presumed gas-water contact, gas saturation of sandstone reservoirs continually decreases while water 

saturation simultaneously increases (fi g. 16). Wells that are low 

in the transition zone on the edges of Cotton Valley fi elds in the 

tight-gas-sandstone trend exhibit low initial rates of gas production and high initial rates of water production, as shown by some 

fl ank wells at Caspiana fi eld in fi gures 14 and 15. Hyperbolic 

decline rates of gas production in conjunction with lower gas 

saturations of reservoir sandstones in these transition-zone wells 

result in such low cumulative production of gas that these wells 

are marginally commercial to noncommercial and, in effect, are 

dry holes (Al Taylor, Nomad Geosciences, oral commun., 2000). 

Hence, commercial limits of gas production are reached before 

gas-water contacts can be encountered by development drilling. 

This probably could be documented by mapping cumulative gas 

production or estimated ultimate gas recovery from wells in 

these Cotton Valley fi elds. 

Knowing gas saturations of Cotton Valley reservoir sandstones from log calculations and capillary properties of those 

sandstones from core analyses at Caspiana fi eld in northwestern Louisiana, Al Taylor (Nomad Geosciences, oral commun., 

2000) estimated gas-column heights required to produce those 

gas saturations. From column-height data, he determined the 

position of gas-water contacts below sea level. Estimates made 

in this fashion for the structural level of the gas-water contact 

at Caspiana fi eld using data from a number of wells cluster 

within a zone about 75 ft thick, suggesting the presence of 

a single gas-water contact for the fi eld. A Cotton Valley well 

situated structurally below this estimated gas-water contact 

reportedly tested water without gas from Cotton Valley sandstones. Because of the vertically extensive gas-water transition 

zones present in fi elds producing gas from tight Cotton Valley 

sandstones in the massive-sandstone trend, Al Taylor (Nomad 

Geosciences, oral commun., 2000) suggests that structural or 

stratigraphic traps with less than 150 ft of vertical closure will 

not have suffi cient gas saturation to produce gas at commercial 

rates.

Figure 16. Schematic diagram of gas-water transition zones in high- and low-permeability reservoirs. Modifi ed from Levorsen (1967).

HIGH PERMEABILITY

(Cotton Valley blanket sandstones)

LOW PERMEABILITY

(Cotton Valley massive sandstones)

CROSS SECTION

OF STRUCTURE

FLUID SATURATION

0 100 50

% Sw

0 100 50

% Sw

TRANSITION ZONE

GAS-WATER CONTACT

WATER

HEIGHTHEIGHT

WATER WATER

GAS

(AND WATER)

GAS GAS

SCHEMATIC DIAGRAM OF TRANSITION ZONES IN

HIGH- AND LOW-PERMEABILITY SANSTONE RESERVOIRS

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 33
In summary, Cotton Valley blanket sandstones across 

northernmost Louisiana have suffi ciently high porosity and 

permeability that gas accumulations exhibit short transition 

zones and have sharp gas-water contacts. Gas fi elds in this 

trend have clearly defi ned productive limits, beyond which 

wells produce water only. However, low-permeability Cotton 

Valley sandstones in the tight-gas massive-sandstone trend 

across northern Louisiana, the Sabine uplift, and East Texas 

Basin display long gas-water transition zones with poorly 

defi ned gas-water contacts. Productive limits of fi elds in this 

trend are diffi cult to defi ne based on data from production tests 

or wireline logs. In conjunction with long gas-water transition 

zones, structural dips are gentle on the fl anks of these gas 

accumulations. As development drilling progresses down the 

fl ank of one of these fi elds through the long gas-water transition zone, gas saturations in the sandstone reservoir decrease 

and water saturations increase. Eventually gas saturations 

become suffi ciently low that, in terms of ultimate cumulative 

gas production, wells become marginally commercial to noncommercial at a structural position still within the transition 

zone above the gas-water contact. Consequently, development 

wells on the fl anks of these gas accumulations generally have 

not encountered gas-water contacts. If drilling and completion 

costs hypothetically were reduced to zero, causing even the 

smallest amount of gas recovery to be commercial, development drilling could progress down the full length of transition 

zones, and gas-water contacts probably would be encountered. 

The progressive increase in water saturation with depth within 

these tight-gas Cotton Valley fi elds, therefore, suggests that 

poorly defi ned gas-water contacts are present below the depth 

at which wells become noncommercial. The presence of gaswater contacts in both Cotton Valley blanket- and massivesandstone trends suggests that gas accumulations in these 

trends are conventional and that a basin-centered gas accumulation does not exist within Cotton Valley sandstones in the 

northern Gulf of Mexico Basin. 

Basin-Centered Gas Potential 

within Bossier Shale

A basin-centered, continuous-gas accumulation might 

have been discovered recently in sandstones within the Bossier 

Shale, the lower formation of the Cotton Valley Group. In a 

currently developing play on the western fl ank of the East 

Texas Basin, gas is being produced from turbidite sandstones 

within the Bossier Shale. These turbidite sandstones probably 

are downdip time-equivalent deposits of deltaic sandstones in 

the lower portion of the Cotton Valley and reportedly were 

deposited seaward of the underlying Haynesville Formation 

carbonate platform edge in a slope or lowstand-fan setting. 

Accommodation space was provided by salt withdrawal such 

that updip and lateral traps currently are formed by pinch out 

of sandstone into shale. Two stacked, stratigraphically separate 

Bossier turbidite-fan systems reportedly occur at depths of 

13,000 to 14,000 ft. Two fi elds, Dew and Mimms Creek, with 

combined estimated recoverable reserves of more than one 

TCFG, currently are being developed by Anadarko Petroleum, 

one of the main operators. As of January 2000 (PI-Dwights 

Drilling Wire, Jan 3, 2000; Jan 12, 2000), Anadarko had drilled 

more than 100 wells with only one dry hole in this Bossier sandstone play. Gas-charged sandstones reportedly are overpressured, and no water has been encountered in the system (Exploration Business Journal, 2nd quarter, 2000). Within the upper 

turbidite-fan interval, porosity ranges from 6 to 15 percent and 

permeability from 0.01 to 1.0 mD. Initial production rates from 

wells average 3 to 4 MMCFGD after fracture stimulation and 

decline exponentially with estimated per-well recoveries of 1 to 

5 BCFG. In the lower sandstone interval, porosity ranges from 

9 to 20 percent, permeability from 1 to 10 mD, pressures are 

higher, and initial production rates of as much as 30 MMCFGD 

have been obtained. This play does not seem to involve the 

classic type of basin-centered gas accumulation with the trap 

produced by inherent low permeability of reservoir sandstones. 

Instead, the trap seems to be provided by marine shales that 

completely encase these turbidite sandstones, but the sandstone 

reservoirs are overpressured, seem to lack water and gas-water 

contacts, and are gas-charged over an extensive area, as demonstrated by only one dry hole in more than 100 wells drilled. 

Conclusions

 1. The Cotton Valley Group represents the fi rst major 

infl ux of clastic sediment into the Gulf of Mexico 

Basin. Major depocenters were located in south-central 

Mississippi, along the Louisiana-Mississippi border, 

and in northeastern Texas. Sands supplied by the ancestral Mississippi River drainage along the LouisianaMississippi border were swept westward by longshore 

currents, creating an east-west barrier-island or strandplain system across northern Louisiana that isolated 

a lagoon to the north. More than 1,000 ft of 

stacked barrier-island sands accumulated as the Terryville massive-sandstone complex. Periodic transgressive events reworked barrier-island sands, transporting 

them northward into the lagoon. These transgressive 

sandstones pinch out into lagoonal shales, can be correlated across northern Louisiana, and are referred to 

informally as blanket sandstones.

 2. Two major Cotton Valley sandstone-reservoir trends 

are identifi ed based on reservoir properties and associated characteristics of gas production. Transgressive, 

blanket sandstones across northernmost Louisiana have 

porosities ranging from 10 to 19 percent and permeabilities from 1 to 280 mD. These sandstones fl ow 

gas and (or) liquids during open-hole DST’s and do 

not require fracture-stimulation treatment to produce 

gas at commercial rates. Fields producing from these 

34 Geologic Studies of Basin-Centered Gas Systems
sandstone reservoirs were developed during the 1940’s 

through 1960’s. Cotton Valley massive sandstones to 

the south, and extending westward across the Sabine 

uplift into eastern Texas, exhibit porosities from 6 to 10 

percent and permeabilities generally less than 0.1 mD. 

Designated as tight-gas sandstones by FERC, these 

reservoirs commonly do not fl ow gas or liquids during 

DST’s, and they require fracture-stimulation treatments 

to achieve commercial rates of production. Gas production from these sandstones in eastern Texas and 

northern Louisiana was not established until the mid 

1970’s when advances in hydraulic-fracture techniques 

occurred in conjunction with a signifi cant increase in 

gas prices as a result of price deregulation. 

 3. Porosity and permeability of Cotton Valley sandstones 

are controlled by diagenetic properties, which in turn 

are governed by depositional environment. Although 

diagenetic patterns and mineralogy are complex, highenergy, clean sandstones generally are cemented by 

authigenic quartz and (or) calcite and have poor reservoir properties. In lower energy sandstones, clay 

coatings on quartz grains inhibited development of 

quartz overgrowths, resulting in preservation of primary porosity. High clay content, however, generally 

imparts poor permeability to these sandstones. The best 

reservoir sandstones are those which have experienced 

development of signifi cant secondary porosity from 

dissolution of calcite cement and unstable framework 

grains. 

 4. The complex diagenetic mineralogy of tight Cotton 

Valley sandstones precludes use of standard calculation 

methods in reservoir evaluation with wireline logs. 

Bound water associated with pore-fi lling clays or clay 

coatings and conductive minerals such as pyrite result 

in abnormally low resistivity measurements leading to 

such high calculated water saturations that productive 

zones often appear wet. Also resulting in erroneous 

reservoir evaluations are pessimistic measurements of 

porosity with wireline logs caused by the presence 

of high-density carbonate minerals such as ankerite 

and siderite. Therefore, without lithologic data from 

cores or drill cuttings to calibrate wireline logs, such 

logs are of limited value in differentiating between 

gas-productive and wet intervals and therefore are of 

limited value in identifying gas-water contacts on the 

fl anks of Cotton Valley fi elds. 

 5. Abnormally high reservoir pressures with fl uidpressure gradients exceeding 0.55 psi/ft occur in 

Cotton Valley sandstones in northeastern Louisiana. 

The boundary between the overpressured area on the 

east and normally pressured region to the west cuts 

across the permeable, blanket- and tight, massive-sandstone trends such that overpressures occur within both 

reservoir trends. Within the blanket-sandstone trend, 

where pressure data are more abundant, some Cotton 

Valley fi elds are overpressured whereas adjacent fi elds 

are normally pressured. Also, within certain fi elds, 

some of the stacked blanket sandstones are overpressured whereas others are normally pressured. Such 

compartmentalization of overpressured reservoirs in 

proximity to normally pressured ones, rather than 

development of overpressure on a regional scale, suggests that these blanket-sandstone fi elds are conventional gas accumulations and not part of a basin-centered gas accumulation. Also, the occurrence of normally pressured reservoirs across the majority of the 

tight, Cotton Valley massive-sandstone trend is not 

indicative of presence of a basin-centered, continuous 

gas accumulation. Geographic distribution of overpressures in Cotton Valley sandstones suggests that overpressuring was caused by “infl ation” of existing pressures in tightly sealed reservoirs by gases derived from 

emplacement of the nearby Jackson (igneous) dome.

 6. Gas found in Cotton Valley sandstone reservoirs is 

believed to be derived from (1) interbedded Cotton 

Valley marine shales, (2) underlying marine shales of 

the Bossier Shale, and (or) (3) stratigraphically lower, 

Jurassic Smackover laminated, lime mudstones. These 

source rocks are believed to have been buried to suffi cient depths relative to the regional geothermal gradient to have generated dry gas during the past 60 m.y. 

Timing of gas generation and migration is favorable 

because it postdates development of the Sabine uplift, 

smaller structures on and fl anking the uplift, and salt 

structures in the East Texas and Northern Louisiana 

Salt Basins. Stratigraphic proximity of source rocks 

to Cotton Valley sandstone reservoirs and appropriate 

thermal maturity and time of generation and migration 

would be consistent with interpretation of a potential 

basin-centered gas accumulation.

 7. Presence of a gas-water contact is perhaps the most 

defi nitive criterion suggesting that a gas accumulation 

is conventional rather than a “sweetspot” within a 

basin-centered, continuous gas accumulation. Within 

the Cotton Valley blanket-sandstone trend across northernmost Louisiana, short gas-water transition zones 

and well-defi ned gas-water contacts have been reported 

in seven gas fi elds. Relatively high porosity and permeability of blanket sandstones and associated high gasproduction rates achieved without fracture stimulation 

throughout the trend suggest that all gas fi elds within 

the blanket-sandstone trend probably have well-defi ned 

gas-water contacts; therefore, these gas accumulations 

are conventional.

 8. Within the tight, massive-sandstone trend, porosity and 

permeability are suffi ciently low that gas-water transition zones are long and gas-water contacts poorly 

defi ned. Productive limits of these tight-gas-sandstone 

Cotton Valley fi elds are not defi ned by wells that 

encounter a gas-water contact or test water without 

gas from a zone below a gas-water contact, as in the 

blanket-sandstone trend. With increasing depth through 

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 35
vertically extensive gas-water transition zones, gas saturation in reservoir sandstones decreases and water 

saturation increases. Eventually gas saturations become 

suffi ciently low that, in terms of cumulative gas production, wells become marginally commercial to noncommercial at a structural position still within the transition zone above the gas-water contact. Therefore, 

development wells on the fl anks of gas accumulations 

in the tight, Cotton Valley massive-sandstone trend 

rarely encounter gas-water contacts. If even the smallest amount of gas recovery were commercial, development drilling probably would progress down the 

full length of transition zones, and gas-water contacts 

would be encountered in these gas accumulations. The 

presence of gas-water contacts in gas accumulations 

within the tight, Cotton Valley massive-sandstone trend 

suggests that accumulations in this trend, too, are conventional and that a basin-centered gas accumulation 

does not exist within Cotton Valley sandstones in the 

northern Gulf of Mexico Basin.

 9. A basin-centered, continuous gas accumulation might 

occur in turbidite sandstones within the Bossier Shale, 

the lower formation of the Cotton Valley Group. In a 

currently developing play on the western fl ank of East 

Texas Basin, gas production with estimated recoverable 

reserves exceeding one TCFG is being obtained from 

sandstone reservoirs, interpreted as slope or lowstandfan deposits, that are completely encased in marine 

shales. Reservoirs are signifi cantly overpressured and 

no water has been encountered in the system. More 

than 100 successful wells and only one dry hole have 

been drilled.

References Cited

Almon, W.R., 1979, A geologic appreciation of shaly sands: Society 

of Professional Well Log Analysts, Twentieth Annual Logging 

Symposium, p. WW 1–WW14.

Bebout, D.G., White, W.A., Garrett, C.M., Jr., and Henz, T.F., 1992, Atlas 

of major central and eastern Gulf Coast gas reservoirs: University 

of Texas at Austin, Bureau of Economic Geology, 88 p.

Black, C.E., and Berg, R.R., 1987, Fan-delta reservoirs in the lower 

Cotton Valley Group (Jurassic), Kildare fi eld, northeast Texas: Gulf 

Coast Association of Geological Societies Transactions, v. 37, 

p. 35–42.

Bruce, P.L., Hunter, J.L., Kuhlman, R.D., and Weinheimer, D.D., 1992, 

New fracturing techniques reduce tight gas sand completion 

problems: Oil and Gas Journal, v. 90, no. 41, p. 72–76. 

CER Corporation, and S.A. Holditch & Associates, eds., 1991, Staged 

fi eld experiment no. 3: Application of advanced technologies in 

tight-gas sandstones—Travis Peak and Cotton Valley Formations, 

Waskom fi eld, Harrison County, Texas: Gas Research Institute 

Report 91/0048, 253 p.

Coleman, J.L., Jr., and Coleman, C.J., 1981, Stratigraphic, 

sedimentologic and diagenetic framework for the Jurassic Cotton 

Valley Terryville massive sandstone complex, northern Louisiana: 

Gulf Coast Association of Geological Societies Transactions, v. 31, 

p. 71–79.

Coleman, J.L., Jr., 1985, Diagenesis of Cotton Valley Sandstone 

(Upper Jurassic), east Texas: Implications for tight-gas formation 

pay recognition: Discussion: American Association of Petroleum 

Geologists Bulletin, v. 69, no. 5, p. 813–815.

Collins, S.E., 1980, Jurassic Cotton Valley and Smackover reservoir 

trends, east Texas, north Louisiana, and south Arkansas: American 

Association of Petroleum Geologists Bulletin, v. 64, no. 7, 

p. 1004–1013.

Dow, W.G., 1978, Petroleum source beds on continental slopes and 

rises: American Association of Petroleum Geologists Bulletin, v. 62, 

no. 9, p. 1584–1606.

Dutton, S.P., 1987, Diagenesis and burial history of the Lower 

Cretaceous Travis Peak Formation, east Texas: University of Texas, 

Bureau of Economic Geology, Report of Investigations No. 164, 58 p.

Dutton, S.P., Clift, S.J., Hamilton, D.S., Hamlin, H.S., Hentz, T.F., 

Howard, W.E., Akhter, M.S., and Laubach, S.E, 1993, Major lowpermeability sandstone gas reservoirs in the continental United 

States: University of Texas, Bureau of Economic Geology, Report of 

Investigations No. 211, 221 p.

Eversull, L.G., 1985, Depositional systems and distribution of Cotton 

Valley blanket sandstones in northern Louisiana: Gulf Coast 

Association of Geological Societies Transactions, v. 35, p. 49–57.

Finley, R.J., 1984, Geology and engineering characteristics of selected 

low-permeability gas sandstones: A national survey: University of 

Texas, Bureau of Economic Geology, Report of Investigations No. 

138, 220p.

Finley, R.J., 1986, An overview of selected blanket-geometry, lowpermeability gas sandstones in Texas, in Spencer, C.W., and Mast, 

R.F., eds., Geology of Tight-Gas Reservoirs: American Association 

of Petroleum Geologists Studies in Geology No. 24, p. 69–85.

Ganer, B.L., 1985, Case history of Cotton Valley sand log interpretation 

for a north Louisiana fi eld: Journal of Petroleum Technology, v. 37, 

no. 11, p. 1995 –2005.

Gies, R.M., 1984, Case history for a major Alberta deep-basin gas 

trap: The Cadomin Formation, in Masters, J.A., ed., Elmworth—

Case Study of a Deep-Basin Gas Field: American Association of 

Petroleum Geologists Memoir 39, p. 115–140.

Hall, C.D., Janks, J.S., and Ladle, G.H., 1984, Sedimentology and 

diagenesis of the Cotton Valley Sandstone in the Amoco No. 

1 Cullers well, Rusk County, Texas, in Presley, M.W., ed., The 

Jurassic of East Texas: Tyler, Texas, East Texas Geological Society, 

p. 127–140.

Herrmann, L.A., Lott, J.A., and Davenport, R.E., 1991, Ruston fi eld—

U.S.A., Gulf Coast Basin, Louisiana, in Beaumont, E.A., and Foster, 

N.H., eds., American Association of Petroleum Geologists Treatise 

of Petroleum Geology, Structural Traps V, p. 151–186.

Jackson, M.L.W., and Laubach, S.E., 1991, Structural history and origin 

of the Sabine arch, east Texas and northwest Louisiana: University 

of Texas at Austin, Bureau of Economic Geology, Geological 

36 Geologic Studies of Basin-Centered Gas Systems
Circular 91-3, 47 p.

Janks, J.S., Sanness, T., and Rasmussen, B.A., 1985, Diagenesis of 

the Cotton Valley sandstones, Catahoula Creek fi eld, southern 

Mississippi: Gulf Coast Association of Geological Societies 

Transactions, v. 35, p. 415–423.

Jennings, A.R., and Sprawls, B.T., 1977, Successful stimulation in the 

Cotton Valley Sandstone—A low-permeability reservoir: Journal of 

Petroleum Technology, v. 29, no. 10, p. 1267–1276.

Jones, P.H., 1977, Geopressuring mechanism of Smackover gas 

reservoirs, Jackson dome area, Mississippi: Discussion: Journal of 

Petroleum Technology, v. 29, no. 5, p.584–585.

Kast, J.A., 1983, Depositional environments of Schuler Formation 

(Cotton Valley sands), Upshur County, Texas [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 67, no. 3, p. 493.

Kosters, E.C., Bebout, D.G., Seni, S.J., Garrett, C.M., Jr., Brown, L.F., 

Jr., Hamlin, H.S., Dutton, S.P., Ruppel, S.C., Finley, R.J., and Tyler, 

Noel, 1989, Atlas of major Texas gas reservoirs: University of Texas 

at Austin, Bureau of Economic Geology, 161 p.

Laubach, S.E., and M.L.W. Jackson, 1990, Origin of arches in the 

northwestern Gulf of Mexico Basin: Geology, v. 18, p. 595–598.

Law, B.E., and Dickinson, W.W., 1985, Conceptual model for origin 

of abnormally pressured gas accumulations in low-permeability 

reservoirs: American Association of Petroleum Geologists Bulletin, 

v. 69, no. 8, p. 1295–1304.

Law, B.E., and Spencer, C.W., 1993, Gas in tight reservoirs—An 

emerging major source of energy, in Howell, D.G., ed., The Future 

of Energy Gases: U.S. Geological Survey Professional Paper 1570, 

p. 233–252.

Levorsen, A.I., 1967, Geology of petroleum: San Francisco, W.H. 

Freeman and Co., 724 p.

Lopatin, N.V., 1971, Temperature and geologic time as factors of 

carbonifi cation [in Russian]: Izvestiya Akademii Nauk SSSR, Seriya 

Geologischeskaya, no 3., p. 95–106.

Mann, C.J., and Thomas, W.A., 1964, Cotton Valley Group (Jurassic) 

nomenclature, Louisiana and Arkansas: Gulf Coast Association of 

Geological Societies Transactions, v. 14, p. 143–152.

McGowen, M.K., and Harris, D.W., 1984, Cotton Valley (Upper 

Jurassic) and Hosston (Lower Cretaceous) depositional systems 

and their infl uence on salt tectonics in the East Texas Basin: 

University of Texas, Bureau of Economic Geology, Geological 

Circular 84-5, 41p.

Meehan, D.N., and Pennington, B.F., 1982, Numerical simulation 

results in the Carthage Cotton Valley fi eld: Journal of Petroleum 

Technology, v. 34, no. 1, p. 189–198.

Moore, T., 1983, Cotton Valley depositional systems of Mississippi: 

Gulf Coast Association of Geological Societies Transactions, v. 33, 

p. 163–167.

Nangle, P., Fertl, W.H., and Frost, E., Jr., 1982, What to expect when 

logging the Cotton Valley trend: World Oil, v. 195, no. 5, p. 175–195.

Parker, C.A., 1972, Geopressures in the Smackover on Mississippi, in 

Abnormal Subsurface Pressure Symposium, Baton Rouge: Society 

of Petroleum Engineers SPE 3885, p.109–114.

Pate, B.F., 1963, Signifi cant north Louisiana Cotton Valley stratigraphic 

traps: Gulf Coast Association of Geological Societies Transactions, 

v. 13, p. 177–183. 

Pate, B.P., and Goodwin, R.N., 1961, Calhoun fi eld, Jackson, Lincoln, 

Ouachita Parishes, Louisiana: Gulf Coast Association of Geological 

Societies Transactions, v. 11, p. 197–201.

Presley, M.W., and Reed, C.H., 1984, Jurassic exploration trends of 

east Texas, in Presley, M.W., ed., The Jurassic of East Texas: Tyler, 

Texas, East Texas Geological Society, p. 11–22.

Royden, L., Sclater, J.G., and Von Herzen, R.P., 1980, Continental 

margin subsidence and heat fl ow: Important parameters in 

formation of petroleum hydrocarbons: American Association of 

Petroleum Geologists Bulletin, v. 64, no. 2, p. 173–187.

Russell, B.J., Jr., Sartin, A.A., and Ledger, E.B., 1984, Depositional and 

diagenetic history of the Bodcaw Sand, Cotton Valley Group (Upper 

Jurassic), Longwood fi eld, Caddo Parish, Louisiana: Gulf Coast 

Association of Geological Societies Transactions, v. 34, p. 217–228.

Salvador, A., 1987, Late Triassic-Jurassic paleogeography and origin 

of Gulf of Mexico Basin: American Association of Petroleum 

Geologists Bulletin, v. 71, no. 4, p. 419–451.

Sassen, R., and Moore, C.H., 1988, Framework of hydrocarbon 

generation and destruction in eastern Smackover trend: American 

Association of Petroleum Geologists Bulletin, v. 72, no. 6, 

p. 649–663.

Saucier, A.E., 1985, Geologic framework of the Travis Peak (Hosston) 

Formation of east Texas and north Louisiana, in Finley, R.J., 

Dutton, S.P., Lin, Z.S., and Saucier, A.E., The Travis Peak (Hosston) 

Formation: Geologic Framework, Core Studies, and Engineering 

Field Analysis: University of Texas, Bureau of Economic Geology, 

[contract report prepared for the Gas Research Institute under 

contract no. 5082-211-0708], 233 p.

Scardina, A.D., 1981, Tectonic subsidence history of the North 

Louisiana Salt Basin: Louisiana State University, M.S. thesis, 103 p.

Schenk, C.J., and Viger, R.J., 1996, East Texas Basin and MississippiLouisiana Salt Basins provinces, Region 6—Gulf Coast, geologic 

framework, in Gautier, D.L., Dolton, G.L., Takahashi, K.I., and Varnes, 

K.L., eds., 1995 National Assessment of United States Oil and 

Gas Resources—Results, Methodology, and Supporting Data: U.S. 

Geological Survey Digital Data Series DDS-30, release 2.

Schmoker, J.W., 1996, Method for assessing continuous-type 

(unconventional) hydrocarbon accumulations, in Gautier, D.L., 

Dolton, G.L., Takahashi, K.I., and Varnes, K.L., eds., 1995 National 

Assessment of United States Oil and Gas Resources—Results, 

Methodology, and Supporting Data: U.S. Geological Survey Digital 

Data Series 30, release 2.

Shreveport Geological Society, 1946, Reference report on certain oil 

and gas fi elds of north Louisiana, south Arkansas, Mississippi, and 

Alabama: Shreveport Geological Society Reference Volume I, 333 p.

Shreveport Geological Society, 1947, Reference report on certain oil 

and gas fi elds of north Louisiana, south Arkansas, Mississippi, 

and Alabama: Shreveport Geological Society Reference Volume II, 

503 p.

Shreveport Geological Society, 1951, Reference report on certain oil 

and gas fi elds of north Louisiana, south Arkansas, Mississippi, and 

Is There a Basin-Centered Gas Accumulation in Cotton Valley Group Sandstones, Gulf Coast Basin, U.S.A.? 37
Alabama: Shreveport Geological Society Reference Volume III, no. 

1, 42 p.

Shreveport Geological Society, 1953, Reference report on certain oil 

and gas fi elds of north Louisiana, south Arkansas, Mississippi, and 

Alabama: Shreveport Geological Society Reference Volume III, no. 

2, 109 p.

Shreveport Geological Society, 1958, Reference report on certain oil 

and gas fi elds of north Louisiana, south Arkansas, Mississippi, 

and Alabama: Shreveport Geological Society Reference Volume IV, 

204 p.

Shreveport Geological Society, 1963, Report on selected north 

Louisiana and south Arkansas oil and gas fi elds and regional 

geology: Shreveport Geological Society Reference Volume V, 202 p.

Shreveport Geological Society, 1980, Report on selected oil and gas 

fi elds, north Louisiana and south Arkansas: Shreveport Geological 

Society Reference Volume VI, 160 p.

Shreveport Geological Society, 1987, Report on selected oil and gas 

fi elds, Ark-La-Tex and Mississippi: Shreveport Geological Society 

Reference Volume VII, 153 p.

Sloane, B.J., Jr., 1958, The subsurface Jurassic Bodcaw sand in 

Louisiana: Louisiana Geological Survey, Geological Bulletin No. 33, 

33 p.

Snedden, J.W., 1984, Validity of the use of the spontaneous potential 

curve shape in the interpretation of sandstone depositional 

environments: Gulf Coast Association of Geological Societies 

Transactions, v. 34, p. 255–263.

Sonnenberg, S.A., 1976, Interpretation of Cotton Valley depositional 

environment from core study, Frierson fi eld, Louisiana: Gulf Coast 

Association of Geological Societies Transactions, v. 26, p. 320–325.

Spencer, C.W., 1987, Hydrocarbon generation as a mechanism for 

overpressuring in Rocky Mountain region: American Association of 

Petroleum Geologists Bulletin, v. 71, no. 4. p. 368–388.

Studlick, J.R.J., Shew, R.D., Basye, G.L., and Ray, J.R., 1990, A 

giant carbon dioxide accumulation in the Norphlet Formation, 

Pisgah anticline, Mississippi, in Barwis, J.H., McPherson, J.C., and 

Studlick, J.R.J., eds., Sandstone Petroleum Reservoirs: New York, 

Springer-Verlag, p. 181–203.

Swain, F.M., 1944, Stratigraphy of Cotton Valley beds of northern 

Gulf Coastal Plain: Amerdican Association of Petroleum Geologists 

Bulletin, v. 28, no. 5. p. 577–614.

Thomas, W.A., and Mann, C.J., 1963, Correlation chart of the upper 

Cotton Valley sands, in Herrmann, L.A., ed., Shreveport Geological 

Society Reference Report, v. V, p. 9–17.

Thomas, W.A., and Mann, C.J., 1966, Late Jurassic depositional 

environments, Louisiana and Arkansas: American Association of 

Petroleum Geologists Bulletin, v. 50, no. 1. p. 178–182.

Tindall, W.A., Neal, J.K., and Hunter, J.C., 1981, Evolution of fracturing 

the Cotton Valley sands in Oak Hill fi eld: Journal of Petroleum 

Technology, v. 33, no. 5, p.799–807.

Tissot, B.P., and Welte, D.H., 1978, Petroleum formation and 

occurrence: New York, Springer-Verlag, 538 p.

Trojan, M., 1985, Effects of diagenesis on reservoir properties and log 

response, Upper Jurassic Taylor sandstone, Cotton Valley Group, 

Lincoln Parish, Louisiana: Gulf Coast Association of Geological 

Societies Transactions, v. 35, p. 515–523.

Turner, J.R. 1997, Recognition of low resistivity, high permeability 

reservoir beds in the Travis Peak and Cotton Valley of east Texas: 

Gulf Coast Association of Geological Societies Transactions, v. 47, 

p. 585–593.

Wapples, D.W., 1980, Time and temperature in petroleum formation: 

Application of Lopatin’s method to petroleum exploration: American 

Association of Petroleum Geologists Bulletin, v. 64, no. 6, 

p. 916–926.

Wescott, W.A., 1983, Diagenesis of Cotton Valley Sandstone (Upper 

Jurassic), east Texas: Implications for tight gas formation 

pay recognition: American Association of Petroleum Geologists 

Bulletin, v. 67, no. 6, p. 1002–1013.

Wescott, W.A., 1985, Diagenesis of Cotton Valley Sandstone (Upper 

Jurassic), east Texas: Implications for tight gas formation pay 

recognition: Reply: American Association of Petroleum Geologists 

Bulletin, v. 69, no. 5, p. 816–818.

Wescott, W.A., and Hood, W.C., 1991, Hydrocarbon generation and 

migration routes in the East Texas Basin: Gulf Coast Association of 

Geological Societies Transactions, v. 41, p. 675.

White, W.A., and Garrett, C.M., Jr., 1992, KJ-1. Hosston Formation and 

Cotton Valley Group sandstones—Sabine uplift, in Bebout, D.G., 

White, W.A., Garrett, C.M., Jr., and Hentz, T.F., eds., Atlas of Major 

Central and Eastern Gulf Coast Gas Reservoirs: University of Texas, 

Bureau of Economic Geology, p. 63–64.

White, W.A., Garrett, C.M., Jr., and Woodward, M., 1992, JS-1. Cotton 

Valley shallow-marine sandstone—ARKLA region, in Bebout, D.G., 

White, W.A., Garrett, C.M., Jr., and Hentz, T.F., eds., Atlas of Major 

Central and Eastern Gulf Coast Gas Reservoirs: University of Texas, 

Bureau of Economic Geology, p. 72–74.

Wilson, D.A., and Hensel, W.M., 1984, The Cotton Valley Sandstone of 

east Texas: A log-core study, in Presley, M.W., ed., The Jurassic of 

East Texas: Tyler, Texas, East Texas Geological Society, p. 141–152.

Worrall, D.M., and Snelson, S., 1989, Evolution of the northern Gulf of 

Mexico, with emphasis on Cenozoic growth faulting and the role 

of salt, in Bally, A.W., and Palmer, A.R., eds., The Geology of North 

America; An Overview: Geological Society of America, The Geology 

of North America Series, v. A, p. 97–138.

Manuscript approved for publication October 26, 2001

Published in the Central Region, Denver, Colorado

Editing, layout, photocomposition—Richard W. Scott, Jr.

Cover design, graphics consultation—Carol A. Quesenberry

Graphics by the authors

38 Geologic Studies of Basin-Centered Gas Systems