U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2015–3078

December 2015

Introduction

The U.S. Geological Survey (USGS) completed a 

geology-based assessment of continuous (unconventional) 

oil and gas resources of the Mississippian Barnett Shale 

within the Bend Arch–Fort Worth Basin Province of northcentral Texas (fig. 1). The Barnett Shale was last assessed in 

this region by the USGS in 2003, and that assessment was 

based solely on vertical drilling development (Pollastro and 

others, 2004). Since 2003, horizontal drilling has taken precedence, with more than 16,000 horizontal wells and 4,700 

vertical wells drilled into the Barnett Shale since exploitation of the formation began. More than 15 trillion cubic feet 

of gas (TCFG) and 59 million barrels of oil (MMBO) have 

been produced from the Barnett Shale since the 2003 assessment (IHS Energy Group, 2015). 

Geologic Summary

The Barnett Shale was deposited during the Late Mississippian within a narrow, restricted seaway during the initial 

formation of the Bend Arch–Fort Worth Basin. The shale is 

mainly composed of siliceous and calcareous mudstone, with 

a total organic carbon content ranging from 2 to 6 weight 

percent (Bruner and Smosna, 2011). The formation is thickest 

(greater than 1,000 feet) in the structurally deepest part of the 

basin, southwest of the Muenster arch (fig. 1; Pollastro and 

others, 2007). The Barnett Shale is divided into upper and 

lower units where the Forestburg limestone is present; however, the Barnett Shale is considered undifferentiated beyond 

the lateral extent of this unit. The underlying Viola-Simpson 

Group and overlying Marble Falls Formation may serve as 

fracture barriers where present, but they do not preclude drilling outside their extents (Pollastro and others, 2007). 

The Barnett Shale serves as the primary source rock and as 

a reservoir in the Bend Arch–Fort Worth Basin. Hydrocarbons 

generated from the Barnett have also migrated into overlying 

conventional reservoirs, forming the Barnett-Paleozoic Total 

Petroleum System (TPS). Production from the Barnett Shale is 

contingent on thermal maturity, which has been primarily based 

on vitrinite reflectance studies and on formation parameters 

such as porosity and thickness (Browning and others, 2013; 

Fu and others, 2015). For this assessment, thermal maturity 

is based on the hydrogen index (HI); where, based on recent 

USGS research, HI less than 100 represents primary and secondary gas 

generation (with secondary gas predominant at HI less than 50), and HI 

greater than 100 represents primarily oil generation.

Assessment Units

The three Barnett Shale assessment units (AUs) that were defined 

for the Barnett-Paleozoic TPS are as follows: (1) Barnett Continuous Gas 

AU, (2) Barnett Mixed Continuous Gas and Oil AU, and (3) Western 

Barnett Continuous Oil AU (fig. 1). The Barnett Continuous Gas AU is 

bounded by the eastern extent of the Barnett Shale and contained within 

the area where HI is less than 100. In the Barnett Continuous Gas AU, 

the geologic “sweet spot” is defined by HI less than 50. The Barnett 

Mixed Continuous Gas and Oil AU is adjacent to the Barnett Continuous 

Gas AU, where HI is equal to 100 delineates the boundary between the 

Barnett Mixed Continuous Gas and Oil AU and the Barnett Continuous 

Gas AU. The HI values within the Barnett Mixed Continuous Gas and 

Oil AU are therefore greater than 100. The northeastern extent of the 

Barnett Mixed Continuous Gas and Oil AU is limited to the extent of the 

Barnett Shale, and the AU covers an area where the formation thickness exceeds 100 feet in this region of the Bend Arch–Fort Worth Basin. 

The 100 foot isopach contour delineates the western edge of the Barnett 

Mixed Continuous Gas and Oil AU. The Western Barnett Continuous Oil AU is adjacent to both the Barnett Continuous Gas and Barnett 

Mixed Continuous Gas and Oil AUs, where formation thickness is less 

than 100 feet in the northern area of the AU (limit of the Barnett Mixed 

Figure 1. Map of the Bend Arch–Fort Worth Basin Province (blue outline) 

and three Barnett Shale assessment units.

Using a geology-based assessment methodology, the U.S. 

Geological Survey estimated mean volumes of 53 trillion 

cubic feet of shale gas, 172 million barrels of shale oil, and 

176 million barrels of natural gas liquids in the Barnett 

Shale of the Bend Arch–Fort Worth Basin Province of Texas.

National and Global Petroleum Assessment

Assessment of Undiscovered Shale Gas and Shale Oil Resources 

in the Mississippian Barnett Shale, Bend Arch–Fort Worth Basin 

Province, North-Central Texas

Bend Arch-Fort Worth Basin Province

OKLAHOMA

TEXAS

Barnett

Continuous

Gas AU

−102° −101° −100° −99° −98° −97° −96°

35°

34°

33°

32°

31°

30°

KS MO

AR

LA

NM

CO

OK

TX

GULF OF

MEXICO

Area of 

study

Barnett Mixed Continuous 

Gas and Oil AU

Bend Arch-Fort Worth Basin

Barnett Continuous Gas AU

Barnett Mixed Continuous Gas 

 and Oil AU

Western Barnett Continuous Oil AU

EXPLANATION

State boundary

County boundary

Source: National Park Service

Western Barnett 

Continuous Oil AU

(not quantitatively

assessed)

0 100 KILOMETERS 50

0 50 100 MILES

Muenster

 arch

MEXICO

MEXICO
ISSN 2327-6916 (print) ISSN 2327-6932 (online) http://dx.doi.org/10.3133/fs20153078

Continuous Gas and Oil AU) and where HI is greater 

than 100 (limit of the Barnett Continuous Gas AU). 

The western boundary of the Western Barnett Continuous Oil AU is defined by the western extent of the Barnett Shale. No sweet spots were defined for the Barnett 

Mixed Continuous Gas and Oil and Western Barnett 

Continuous Oil AUs, and the latter was not quantitatively assessed because of minimal drilling within the 

AU. Key input data used to assess the continuous AUs 

are listed in table 1.

Resource Summary

The USGS assessed technically recoverable continuous (unconventional) resources for two AUs defined 

in the Barnett Shale, resulting in total estimated means of 

53 trillion cubic feet of natural gas (TCFG), 172 million 

barrels of oil (MMBO), and 176 million barrels of natural 

gas liquids (MMBNGL; table 2). These total estimated 

means include mean estimated natural gas resources of 

48.3 TCFG within the Barnett Continuous Gas AU (with 

a mean of 61 MMBNGL) and of 3.3 TCFG within the 

Barnett Mixed Continuous Gas and Oil AU. In addition, 

means of 172 MMBO, 1.4 TCFG, and 115 million barrels of natural gas liquids were estimated for the Barnett 

Mixed Continuous Gas and Oil AU (table 2). 

References Cited

Browning, J., Tinker, S.W., Ikonnikova, S., Gulen, G., Potter, E., 

Fu, Q., Horvath, S., Patzek, T., Male, F., Fisher, W., Roberts, 

F., and Medlock K., III, 2013, Barnett Shale model-1—Study 

develops decline analysis, geologic parameters for reserves, 

production forecast: Oil & Gas Journal, v. 111, no. 8, p. 63–71.

Bruner, K.R., and Smosna, R., 2011, A comparative study of the 

Mississippian Barnett Shale, Fort Worth Basin, and Devonian 

Marcellus Shale, Appalachian Basin: Technical Report DOE/

NETL–2011/1478, National Energy Technology Laboratory 

(NETL) for the U.S. Department of Energy, 106 p.

Fu, Q., Horvath, S.C., Potter, E.C., Roberts, F., Tinker, S.W., 

Ikonnikova, S., Fisher, W.L., and Yan, J., 2015, Log-derived 

thickness and porosity of the Barnett Shale, Fort Worth Basin, 

Texas—Implications for assessment of gas shale resources: 

AAPG Bulletin, v. 99, no. 1, p. 119–141.

IHS Energy Group, 2015, Petroleum information database: Available from IHS Energy, 15 Inverness Way East, Englewood, 

Colo., 80112.

Pollastro, R.M., Hill, R.J., Ahlbrandt, T.A., Charpentier, R.R., 

Cook, T.A., Klett, T.R., Henry, M.E., and Schenk, C.J., 2004,

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

Barnett-Paleozoic TPS

Barnett Continuous Gas AU 1.0 Gas 36,929 47,666 61,978 48,313 34 60 92 61

Barnett Mixed Continuous Gas and Oil AU 1.0 Oil 107 166 254 172 873 1,358 2,080 1,401 22 40 68 42

1.0 Gas 1,916 3,132 5,099 3,271 40 69 118 73

Western Barnett Continuous Oil AU Not quantitatively assessed

Total undiscovered unconventional resources 107 166 254 172 39,718 52,156 69,157 52,985 96 169 278 176

Table 2. Assessment results for continuous oil and gas resources in Barnett Shale of the Bend Arch-Fort Worth Basin Province.

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

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

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

Assessment input data–Continuous AU

Barnett Continuous Gas

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 6,000,000 6,419,000 7,000,000 6,473,000

Average drainage area of wells (acres) 60 100 140 100

Percentage of total AU area that is untested (%) 65 73 80 73

Percentage of untested AU area in sweet spots (%) 15 30 40 28

Success ratio (%) in sweet spots 85 90 92 89

Average EUR (BCFG) in sweet spots 1.0 2.0 3.0 2.034

Success ratio (%) in non-sweet spots 60 75 85 73

Average EUR (BCFG) in non-sweet spots 0.5 0.9 2.0 0.956

AU probability 1.0

Assessment input data–Continuous AU

Barnett Mixed Continuous Gas and Oil

Minimum Mode Maximum Calculated

mean

Potential production area of AU (acres) 1,700,000 2,057,000 2,300,000 2,019,000

Average drainage area of wells (acres) 60 100 140 100

Percentage of total AU area that is untested (%) 75 85 92 84

Percentage of untested wells that are oil wells (%) 40 65 75 60

Success ratio of oil wells (%) 30 45 65 47

Average EUR of oil wells (MMBO) 0.02 0.035 0.05 0.036

Success ratio of gas wells (%) 30 45 65 47

Average EUR of gas wells (BCFG) 0.5 1.0 1.5 1.017

AU probability 1.0

Table 1. Key assessment input data for two continuous assessment units in Barnett 

Shale of the Bend Arch–Fort Worth Basin Province.

[EUR, estimated ultimate recovery per well; MMBO, million barrels of oil; BCFG, billion cubic feet 

of gas; AU, assessment unit; %, percent. The average EUR input is the minimum, median, maximum, 

and calculated mean]

 Assessment of undiscovered oil and gas resources of the Bend 

Arch–Fort Worth Basin Province of north-central Texas and 

southwestern Oklahoma, 2003: U.S. Geological Survey Fact 

Sheet 2004–3022, 2 p.

Pollastro, R.M., Jarvie, D.M., Hill, R.J., and Adams, C.W., 2007, 

Geologic framework of the Mississippian Barnett Shale, Barnett-Paleozoic total petroleum system, Bend Arch–Fort Worth 

Basin, Texas: AAPG Bulletin, v. 91, no. 4, p. 405–436.

Barnett Shale Assessment Team

Kristen R. Marra (Task Leader; kmarra@usgs.gov), Ronald R. 

Charpentier, Christopher J. Schenk, Michael D. Lewan, Heidi 

M. Leathers-Miller, Timothy R. Klett, Stephanie B. Gaswirth, 

Phuong A. Le, Tracey J. Mercier, Janet K. Pitman, and Marilyn E. 

Tennyson.

For Additional Information

Supporting geologic studies of the Barnett Shale and the methodology used in this assessment are in progress. Assessment information can be accessed at the USGS Energy Resources program 

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