U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016–3092

November 2016 Printed on recycled paper

National and Global Petroleum Assessment

Assessment of Undiscovered Continuous Oil Resources in 

the Wolfcamp Shale of the Midland Basin, Permian Basin 

Province, Texas, 2016

Using a geology-based assessment methodology, the U.S. Geological Survey assessed technically recoverable mean resources 

of 20 billion barrels of oil and 16 trillion cubic feet of gas in the Wolfcamp shale in the Midland Basin part of the Permian Basin 

Province, Texas.

Introduction

In 2016, the U.S. Geological 

Survey (USGS) completed a geologybased assessment of undiscovered, technically recoverable continuous petroleum 

resources in the Pennsylvanian–Permian 

Wolfcamp shale (informal name) in the 

Midland Basin of the Permian Basin 

Province of west Texas (fig. 1). This is 

the first USGS evaluation of continuous resources in the Wolfcamp shale in 

the Midland Basin. Since the 1980s, the 

Wolfcamp shale in the Midland Basin has 

been part of the “Wolfberry” play that 

encompasses Mississippian, Pennsylvanian, 

and Lower Permian reservoirs (Hamlin and 

Baumgardner, 2012). This play has traditionally been developed using vertical wells 

that are completed and stimulated in multiple productive stratigraphic intervals that 

include the Wolfcamp shale and overlying 

Spraberry Formation. The Wolfcamp 

shale is being drilled for continuous oil 

using horizontal wells that are hydraulically fractured. More than 3,000 horizontal 

wells have been drilled and completed in 

the Midland Basin Wolfcamp section (IHS 

MarkitTM, 2016).

Figure 1. Map showing the Midland Basin, 

Permian Basin Province, Texas, and the extent 

of the six assessment units (AU). The Midland 

Basin Wolfcamp A Continuous Oil AU and 

Midland Basin Wolfcamp B Upper Continuous 

Oil AU have the same extent.

–104° –103° –102° –101° –100° –99°

34°

33°

32°

31°

30°

TEXAS

NEW 

MEXICO

Abilene

Lubbock

San 

Angelo

Hobbs

Midland

Central Bas ni Platform

Eastern

Shelf

Val Verde Basin

Source: U.S. Department of the Interior National Park Service

EXPLANATION

Midland Basin Wolfcamp B Lower Continuous Oil AU

County boundary

Permian Basin Province (part)

Midland Basin Northern Wolfcamp Continuous Oil AU

Midland Basin Wolfcamp D Continuous Oil AU

Midland Basin Wolfcamp C Continuous Oil AU

Midland Basin Wolfcamp B Upper Continuous Oil AU

Horseshoe atoll 

Midland Basin Wolfcamp A Continuous Oil AU

0 25 50 MILES

0 25 50 KILOMETERS

NEW

MEXICO

OKLAHOMA

TEXAS

MEXICO GULF OF

MEXICO

Area

of study
Geologic Summary

The Permian Basin Province of west 

Texas and southeastern New Mexico 

contains two subbasins, the Delaware 

Basin to the west and the Midland Basin to 

the east, separated by the uplifted Central 

Basin platform. During the Pennsylvanian–

Permian, the Wolfcamp was deposited as 

shallow-water carbonates on the Central 

Basin platform and Eastern shelf (fig. 1) 

and interbedded, finer-grained, organic-rich 

siliciclastic mud with organic-poor, clayrich mud and fine-grained carbonates in 

the deeper part of the Midland Basin. The 

Wolfcamp shale throughout this region is 

mature for oil generation based on thermal 

maturation data (Pawlewicz and others, 

2005). The petroleum industry has divided 

the Wolfcamp shale into four stratigraphic 

units based on petrophysical log signatures 

and landing zones for horizontal wells. 

The uppermost unit is the Wolfcamp A, 

followed by the underlying Wolfcamp B, 

C, and D units, respectively. The eastern 

margin of Wolfcamp shale deposition prograded westward through time, as indicated 

by the larger depositional areas delineated 

in the Wolfcamp C and D assessment units 

(AUs) when compared to the Wolfcamp A 

and B assessment units.

Definition of Assessment Units

Six continuous assessment units were 

defined and quantitatively assessed in the 

Wolfcamp shale in the Midland Basin of 

the Permian Basin Province: (1) Midland 

Basin Wolfcamp A Continuous Oil AU, 

(2) Midland Basin Wolfcamp B Upper 

Continuous Oil AU, (3) Midland Basin 

Wolfcamp B Lower Continuous Oil 

AU, (4) Midland Basin Wolfcamp C 

Continuous Oil AU, (5) Midland 

Basin Wolfcamp D Continuous Oil 

AU, and (6) Midland Basin Northern 

Wolfcamp Continuous Oil AU (fig. 1). 

The six assessment units are within the 

Permian Basin Paleozoic Composite 

Total Petroleum System (TPS) (Schenk 

and others, 2007). The Midland Basin 

Wolfcamp A Continuous Oil AU and 

Wolfcamp B Upper Continuous Oil AU 

were constrained by the Central Basin 

platform to the west, the southern edge 

of the Horseshoe atoll and an area of 

thick Wolfcamp strata to the north, the 

Eastern Shelf margin to the east, and 

the Val Verde Basin Canyon Sandstone 

AU (Schenk and others, 2016) to the 

south. The Midland Basin Wolfcamp B 

Lower Continuous Oil AU is restricted 

to the southern Midland Basin where the 

thickness of the Wolfcamp B exceeds 

500 feet and allows for placement of two 

lateral wells in the Wolfcamp B unit. The 

Midland Basin Wolfcamp C Continuous 

Oil AU is bounded by the Central Basin 

platform on the west, the southern edge 

of the Horseshoe atoll and an area of thick 

Wolfcamp strata to the north, the estimated 

extent of the Wolfcamp C depositional 

boundary using shelf edges mapped by 

Hentz and others (2016) to the east, and 

the Val Verde Basin Canyon Sandstone 

AU (Schenk and others, 2016) to the 

south. The Midland Basin Wolfcamp 

D Continuous Oil AU is defined by the 

Central Basin platform to the west, the 

southern edge of the Horseshoe atoll to 

the north, the mapped extent of Upper 

Pennsylvanian shale to the northeast and 

east, and the Val Verde Basin Canyon 

Sandstone AU (Schenk and others, 2016) 

to the south. The Midland Basin Northern 

Wolfcamp AU is defined by the Midland 

Basin shelf margin to the north and east 

and the southern edge of the Horseshoe 

atoll and the northern boundary of an area 

of thick Wolfcamp strata that was included 

in the AUs to the south. Assessment input 

data for the six AUs are summarized in 

table 1.

Table 1. Key assessment input data for six continuous assessment units in the Wolfcamp shale in the Midland Basin of the Permian Basin 

Province, Texas.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil. The average EUR input is the minimum, median, and 

calculated mean. Shading indicates not applicable]

Assessment input data Midland Basin Wolfcamp A Continuous Oil AU Midland Basin Wolfcamp B Upper Continuous Oil AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 3,000,000 3,495,500 5,814,000 4,103,000 3,000,000 3,523,000 5,814,000 4,112,333

Average drainage area of wells (acres) 60 80 160 100 60 80 160 100

Percentage of area untested in AU 83 85 91 86.3 83 85 91 86.3

Success ratios (%) 92 95 99 95.3 92 95 99 95.3

Average EUR (MMBO) 0.12 0.16 0.3 0.167 0.12 0.16 0.3 0.167

AU probability 1.0 1.0

Assessment input data Midland Basin Wolfcamp B Lower Continuous Oil AU Midland Basin Wolfcamp C Continuous Oil AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 700,000 742,000 2,012,000 1,151,333 1,000,000 2,373,000 6,703,000 3,358,667

Average drainage area of wells (acres) 60 80 160 100 60 80 160 100

Percentage of area untested in AU 68 70 89 75.7 47 77 92 72

Success ratios (%) 92 95 99 95.3 50 70 90 70

Average EUR (MMBO) 0.12 0.16 0.3 0.167 0.03 0.08 0.15 0.083

AU probability 1.0 1.0

Assessment input data Midland Basin Wolfcamp D Continuous Oil AU Midland Basin Northern Wolfcamp Continuous Oil AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 2,000,000 4,885,000 8,915,000 5,266,667 1,000 1,633,000 3,266,000 1,633,333

Average drainage area of wells (acres) 60 80 160 100 60 80 160 100

Percentage of area untested in AU 73 89 94 85.3 97 99 100 98.7

Success ratios (%) 75 85 95 85 10 50 90 50

Average EUR (MMBO) 0.06 0.12 0.25 0.126 0.02 0.06 0.14 0.064

AU probability 1.0 1.0
View from County Road 221 (formerly the Bankhead Highway) in the Sweetwater vicinity of Nolan County, Texas, west of Abilene. Photograph 

used with permission from the Texas Historical Commission.

Total petroleum system

and assessment unit (AU)

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

Permian Basin Paleozoic Composite Total Petroleum System

Midland Basin Wolfcamp A

Continuous Oil AU

1.0 Oil 3,754 5,633 8,483 5,815 2,540 4,453 7,457 4,652 223 436 806 465

Midland Basin Wolfcamp B

Upper Continuous Oil AU

1.0 Oil 3,769 5,644 8,505 5,829 2,557 4,454 7,482 4,663 224 437 811 466

Midland Basin Wolfcamp B

Lower Continuous Oil AU

1.0 Oil 794 1,342 2,351 1,430 554 1,056 2,023 1,144 49 104 215 114

Midland Basin Wolfcamp C

Continuous Oil AU

1.0 Oil 577 1,306 2,728 1,433 417 1,018 2,299 1,146 38 100 241 115

Midland Basin Wolfcamp D 

Continuous Oil AU

1.0 Oil 2,420 4,658 8,262 4,920 1,733 3,657 7,096 3,936 156 357 753 394

Midland Basin Northern 

Wolfcamp Continuous Oil AU

1.0 Oil 116 458 1,139 521 86 357 953 417 8 35 100 42

Total undiscovered

continuous resources

11,430 19,041 31,468 19,948 7,887 14,995 27,310 15,958 698 1,469 2,926 1,596

Table 2. Assessment results for six continuous assessment units in the Wolfcamp shale in the Midland Basin of the Permian Basin Province, Texas.

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For gas 

accumulations, all liquids are included under the natural gas liquids (NGL) category. 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. Shading indicates not applicable]
Pumpjack in rural Texas. Photograph from the Carol M. Highsmith Archive, Library 

of Congress, Prints and Photographs Division.

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered, 

technically recoverable continuous oil and gas resources 

for six AUs defined in the Midland Basin Wolfcamp shale 

of the Permian Basin Province (table 2). Assessed mean 

resources are 19,948 million barrels of oil (MMBO), 

or 20 billion barrels of oil, with an F95–F5 range from 

11,430 to 31,468 MMBO; 15,958 billion cubic feet 

of associated gas (BCFG), or 16 trillion cubic feet of 

associated gas, with an F95–F5 range from 7,887 to 

27,310 BCFG; and 1,596 million barrels of natural gas 

liquids (MMBNGL) with an F95–F5 range from 698 to 

2,926 MMBNGL.

References Cited

Hamlin, H.S., and Baumgardner, R.W., 2012, Wolfberry 

(Wolfcampian-Leonardian) deep-water depositional 

systems in the Midland Basin—Stratigraphy, lithofacies, reservoirs, and source rocks: Bureau of Economic 

Geology, The University of Texas at Austin, Report of 

Investigations No. 277, 61 p.

Hentz, T.F., Ambrose, W.A., and Hamlin, H.S., 2016, 

Upper Pennsylvanian and Lower Permian shelf-tobasin facies architecture and trends, Eastern Shelf of 

the southern Midland Basin, west Texas, in American 

Association of Petroleum Geologists Southwest Section Annual Convention, Abilene, Tex., April 9–12, 

2016, Proceedings: American Association of Petroleum 

Geologists Southwest Section, 3 p.

IHS MarkitTM, 2016, US Well History and Production 

Database: Englewood, CO, IHS Markit, accessed 

August 2016 at http://www.ihsenergy.com. [Available 

from IHS Markit, 15 Inverness Way East, Englewood, 

CO 80112.]

Pawlewicz, Mark, Barker, C.E., and McDonald, S., 2005, 

Vitrinite reflectance data for the Permian Basin, west 

Texas and southeast New Mexico: U.S. Geological 

Survey Open-File Report 2005–1171, 25 p.

Schenk, C.J., Pollastro, R.M., Cook, T.A., Pawlewicz, 

M.J., Klett, T.R., Charpentier, R.R., and Cook, H.E., 

2007, Assessment of undiscovered oil and gas resources 

of the Permian Basin Province of west Texas and 

southeast New Mexico: U.S. Geological Survey Fact 

Sheet 2007–3115, 4 p.

Schenk, C.J., Tennyson, M.E., Klett, T.R., Mercier, T.J., 

Brownfield, M.E., Gaswirth, S.B., Hawkins, S.J., 

Leathers-Miller, H.M., Marra, K.R., Finn, T.M., and 

Pitman, J.K., 2016, Assessment of tight-gas resources in 

Canyon sandstones of the Val Verde Basin, Texas, 2016: 

U.S. Geological Survey Fact Sheet 2016–3039, 2 p.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20163092

Wolfcamp Shale Assessment Team

Stephanie B. Gaswirth, Kristen R. Marra, Paul G. Lillis, Tracey J. 

Mercier, Heidi M. Leathers-Miller, Christopher J. Schenk, Timothy R. 

Klett, Phuong A. Le, Marilyn E. Tennyson, Sarah J. Hawkins, Michael E. 

Brownfield, Janet K. Pitman, and Thomas M. Finn

For More Information

Assessment results are available at the USGS Energy Resources 

Program Web site at http://energy.usgs.gov.