U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2015–3050

August 2015

ISSN 2327-6916 (print) ISSN 2327-6932 (online)

http://dx.doi.org/10.3133/fs20153050

National and Global Petroleum Assessment

Assessment of Undiscovered Oil and Gas Resources in Sandstone 

Reservoirs of the Cotton Valley Group, U.S. Gulf Coast, 2015

Using a geology-based assessment 

methodology, the U.S. Geological Survey 

estimated undiscovered mean volumes 

of 14 million barrels of conventional oil, 

430 billion cubic feet of conventional gas, 

34,028 billion cubic feet of continuous gas, 

and a mean total of 391 million barrels of 

natural gas liquids in sandstone reservoirs 

of the Upper Jurassic–Lower Cretaceous 

Cotton Valley Group in onshore lands and 

State waters of the U.S. Gulf Coast region.

and north Louisiana; production data from 

separate volumes of rock were assigned to each 

to estimate their respective resources. Table 1 

lists key input data used to predict volumes of 

undiscovered petroleum in the four AUs.

The Cotton Valley Updip Oil AU is present between the updip limit of the Cotton Valley 

Group and a regional system of faults. No 

production has been reported to date, so migration pathways and trapping mechanisms remain 

uncertain. Potential conventional accumulations 

would be expected in paralic or fluvial-deltaic 

sandstone of the Schuler Formation.

The Cotton Valley Peripheral Fault System 

Oil and Gas AU forms an envelope around the 

peripheral fault system. The downdip boundary 

of the AU corresponds to the outer margins of 

the East Texas Basin and the North Louisiana 

and Mississippi Salt Basins, and it approximates 

the updip limit of thick Middle Jurassic salt in 

areas between the basins. Reservoirs are predominantly of paralic and fluvial-deltaic facies.

The Cotton Valley Downdip Oil and Gas 

AU includes the aforementioned salt basins and 

intervening areas not included in other AUs. 

The southern boundary of the AU corresponds 

to the approximate downdip limit of sandstone. Reservoirs are fluvial-deltaic and marine 

Figure 1. Map of the U.S. portion of the Gulf of Mexico Basin with the four assessment units (AUs) 

in the Cotton Valley Group.

Introduction

The U.S. Geological Survey (USGS) 

assessed undiscovered oil and gas resources 

in sandstone reservoirs of the Upper Jurassic–

Lower Cretaceous (Tithonian–Berriasian) Cotton 

Valley Group, which is present in the subsurface 

in an arcuate belt from south Texas to the Florida 

Panhandle. The USGS conducts geology-based 

assessments of undiscovered petroleum by 

evaluating components of a total petroleum system (TPS), including source and reservoir rocks, 

seals and traps, and the geohistory of petroleum 

products. Strata in each assessment unit (AU) 

share similar stratigraphic, structural, and 

petroleum-charge histories. The USGS defined 

four AUs for the Cotton Valley Group in the 

Upper Jurassic–Cretaceous–Tertiary Composite 

TPS for the onshore lands and State waters of the 

U.S. Gulf Coast region (fig. 1).

Geologic Model for Assessment

Potential reservoirs in the Cotton Valley 

Group include fluvial-deltaic and shallowmarine “blanket” sandstones of moderate to high 

porosity and permeability and their “massive” 

downdip counterparts with lower porosity and 

permeability (Eoff and others, in press). The 

Upper Jurassic Smackover, Haynesville, and 

Bossier Formations were likely sources of oil 

and gas. Seals are intraformational mudstone or 

thin limestone, and the Knowles Limestone is 

a regional seal. Traps are stratigraphic, structural, or in combination, but low-permeability 

reservoirs can retain petroleum in the absence of 

well-defined closures.

Assessment Units

Three AUs were assessed for conventional oil and gas accumulations, and one AU 

was assessed as a continuous gas accumulation 

(fig. 1). Two of the AUs overlap in east Texas 

sandstones, including the “blanket” tongues 

of sandstone. Oil and gas accumulations are 

associated with low-amplitude salt-related 

structures along basin margins.

The Cotton Valley Tight Sandstone Gas 

AU is mapped accordant with the distribution 

of low-porosity, low-permeability “massive” 

units of the Terryville Sandstone. It extends 

from the southwest corner of the East Texas 

Basin across the Sabine uplift area and northern Louisiana into southern Mississippi.

Resource Summary

The USGS assessed undiscovered oil 

and gas resources for three conventional AUs 

and one continuous AU defined for sandstone 

reservoirs of the Cotton Valley Group, resulting in estimated mean volumes of 14 million 

barrels of oil (MMBO) and 34,458 billion 

cubic feet of gas (BCFG) (table 2). These 

estimates include mean oil resources from the 

Cotton Valley Updip Oil AU (1 MMBO), the 

Cotton Valley Peripheral Fault System Oil and 

Gas AU (2 MMBO), and the Cotton Valley 

Downdip Oil and Gas AU (11 MMBO). Mean 

conventional and continuous gas resources are 

430 BCFG and 34,028 BCFG, respectively, 

with the latter estimate for the Cotton Valley 

Tight Sandstone Gas AU.

Source: U.S. National Park Service

25°

30°

35°

–100° –95° –90° –85°

0 100 200 MILES

0 100 200 KILOMETERS

GULF OF MEXICO

MEXICO

UNITED 

STATES

OKLAHOMA

TEXAS

KANSAS MISSOURI KENTUCKY

ARKANSAS

ALABAMA

TENNESSEE

MISSISSIPPI

GEORGIA

LOUISIANA FLORIDA

Cotton Valley Updip Oil AU

Cotton Valley Peripheral Fault System 

 Oil and Gas AU

EXPLANATION

Cotton Valley Tight Sandstone Gas AU

Area of overlapping AUs

Cotton Valley Downdip Oil and Gas AU

Study area

TX

OK

GA

AR

AL

FL

LA

MS

TN

KS MO KY
Reference Cited

Eoff, J.D., Dubiel, R.F., Pearson, O.N., and 

Whidden, K.J., in press, Geologic framework for the assessment of undiscovered 

oil and gas resources in sandstone 

reservoirs of the Upper Jurassic–Lower 

Cretaceous Cotton Valley Group, U.S. Gulf 

of Mexico region: Gulf Coast Association 

of Geological Societies Transactions, v. 65.

—Jennifer D. Eoff and others

Table 2. Assessment results for three conventional assessment units and one continuous assessment unit in the Cotton Valley Group.

[TPS, total petroleum system; AU, assessment unit; MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. For 

gas accumulations, all liquids are included as NGL (natural gas liquids). Results shown are fully risked estimates. F95 represents a 95 percent chance of at least the amount 

tabulated; other fractiles are defined similarly. Fractiles are additive under the assumption of perfect positive correlation. Gray shading indicates not applicable]

Total petroleum system (TPS) 

and 

assessment units (AUs)

AU

probability

Accumulation 

type

Total undiscovered resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Upper Jurassic–Cretaceous–Tertiary Composite TPS

Cotton Valley Updip Oil AU 0.2 Oil 0 0 8 1 0 0 4 1 0 0 0 0

Gas 0 0 0 0 0 0 0 0

Cotton Valley Peripheral Fault System 

Oil and Gas AU

0.9 Oil 0 2 5 2 0 1 3 1 0 0 0 0

Gas 0 0 0 0 0 0 0 0

Cotton Valley Downdip Oil and Gas AU 1.0 Oil 3 10 24 11 2 6 16 7 0 0 1 0

Gas 162 380 821 421 2 4 10 5

Total conventional resources 3 12 37 14 164 387 844 430 2 4 11 5

Upper Jurassic–Cretaceous–Tertiary Composite TPS

Cotton Valley Tight Sandstone Gas AU 1.0 Gas 13,128 30,152 67,775 34,028 126 328 837 386

Total unconventional resources 13,128 30,152 67,775 34,028 126 328 837 386

Total undiscovered resources 3 12 37 14 13,292 30,539 68,619 34,458 128 332 848 391

Cotton Valley Group Assessment Team

Jennifer D. Eoff, Laura R.H. Biewick, Michael E. Brownfield, Lauri Burke, Ronald R. 

Charpentier, Russell F. Dubiel, Stephanie B. Gaswirth, Nicholas J. Gianoutsos, Scott A. Kinney, 

Timothy R. Klett, Heidi M. Leathers, Tracey J. Mercier, Stanley T. Paxton, Ofori N. Pearson, 

Janet K. Pitman, Christopher J. Schenk, Marilyn E. Tennyson, and Katherine J. Whidden 

For Additional Information

Assessment results also are available at the USGS Energy Resources Program Web site 

(http://energy.usgs.gov).

Table 1. Key assessment input data for three conventional assessment units and one continuous assessment unit in the Cotton Valley Group.

[AU, assessment unit; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil; BCFG, billion cubic feet of gas; %, percent. The average EUR input 

is the minimum, median, maximum, and calculated mean. Gray shading indicates not applicable]

Assessment input data—Conventional AUs

Cotton Valley Updip Oil AU Minimum Median Maximum Calculated mean

Number of oil fields 1 7 15 7.23

Number of gas fields 0 0 0 0.00

Sizes of oil fields (MMBO) 0.5 0.7 10 0.92

Sizes of gas fields (BCFG)

AU probability 0.20

Cotton Valley Peripheral Fault System Oil and Gas AU Minimum Median Maximum Calculated mean

Number of oil fields 1 3 11 3.28

Number of gas fields 0 0 0 0.00

Sizes of oil fields (MMBO) 0.5 0.7 3 0.78

Sizes of gas fields (BCFG)

AU probability 0.90

Cotton Valley Downdip Oil and Gas AU Minimum Median Maximum Calculated mean

Number of oil fields 0 5 20 5.52

Number of gas fields 1 25 100 27.55

Sizes of oil fields (MMBO) 0.5 1.5 20 2.07

Sizes of gas fields (BCFG) 3 10 200 15.37

AU probability 1.00

Assessment input data—Continuous AU

Cotton Valley Tight Sandstone Gas AU Minimum Median Maximum Calculated mean

Potential production area of AU (acres) 2,000,000 3,000,000 12,869,000 5,956,333

Average drainage area of wells (acres) 40 120 180 113

Percentage of total AU area that is untested (%) 85 90 95 90.0

Success ratio (%) 50 70 80 66.7

Average EUR (BCFG) 0.8 1 1.2 1.007

AU probability 1.0