National and Global Petroleum Assessment

Assessment of Undiscovered Oil and Gas Resources in the Spraberry 

Formation of the Midland Basin, Permian Basin Province, Texas, 2017

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3029

May 2017 Printed on recycled paper

Using a geology-based assessment methodology, the U.S. Geological Survey estimated mean resources of 4.2 billion barrels of oil 

and 3.1 trillion cubic feet of gas in the Spraberry Formation of the Midland Basin, Permian Basin Province, Texas.

Introduction

The U.S. Geological Survey (USGS) completed a geologybased assessment of undiscovered, technically recoverable continuous and conventional oil and gas resources in the Spraberry 

Formation within the Midland Basin of the Permian Basin Province 

in west Texas. Historically, the Spraberry Formation has been 

exploited primarily through vertical drilling, and continual increase 

in drilling depths and perforations within both the Spraberry 

Formation and the underlying Wolfcamp shale has resulted in the 

development of the informal Wolfberry play across the Spraberry 

(trend area) field (Hamlin and Baumgardner, 2012; Railroad Commission of Texas, 2014). The Spraberry was last assessed in 2007 

based on historical production from vertical wells (Schenk and 

others, 2007). Since 2007, multiple intervals within the Spraberry 

have been targeted with horizontal drilling.

Geologic Summary

The Lower Permian (Leonardian) Spraberry Formation 

primarily consists of interbedded sandstone, siltstone, carbonate, 

and organic-rich shale, which were deposited in a deepwater 

marine environment in the Midland Basin. The Midland Basin is 

the eastern subbasin of the greater Permian Basin and is rimmed 

by carbonate platforms such as the Central Basin platform, Eastern shelf, and Northern shelf (fig. 1). The Spraberry Formation is 

informally divided into the upper, middle, and lower Spraberry 

intervals (Hamlin and Baumgardner, 2012). In the southern part of 

the basin, production from continuous reservoirs is extensive across 

the greater Spraberry (trend area) field. In the northern section of 

the basin, conventional Spraberry production occurs where multiple 

intervals of the Spraberry Formation and the underlying Dean 

Formation are productive from discrete fields.

Total Petroleum System and Assessment Units

Two continuous and one conventional assessment units (AUs) 

were defined and quantitatively assessed for the Spraberry Formation 

in the Midland Basin: (1) Middle Spraberry Continuous Oil Trend 

AU, (2) Lower Spraberry Continuous Oil Trend AU, and (3) Northern Spraberry Conventional Oil AU (fig. 1). All three assessment 

units are within the Permian Basin Paleozoic Composite Total Petroleum System (Schenk and others, 2007; Gaswirth and others, 2016). 

The two continuous AUs are identical in extent and are bounded to 

the west by the Central Basin platform, to the east by the Eastern 

shelf basin margin, to the north by the approximate southern edge of 

the Horseshoe atoll and to the south by the Val Verde Basin (Schenk 

Figure 1. Map showing key geologic features and the boundaries of 

the continuous and conventional assessment units (AUs) defined for 

the Spraberry Formation in the Midland Basin, Permian Basin Province, 

Texas. The two continuous AUs are identical in extent.

and others, 2016). The Middle Spraberry Continuous Oil Trend AU 

covers the interval of the informal middle Spraberry. The Lower 

Spraberry Continuous Oil Trend AU consists of strata of the informal 

lower Spraberry interval and includes the industry-termed (informal) 

lower Spraberry shale and Jo Mill siltstone. The Northern Spraberry 

Conventional Oil AU encompasses the entire Spraberry Formation 

across the Horseshoe atoll and into the northern part of the basin 

where conventional Spraberry fields exist. The conventional AU is 

bounded by the shelf margins of the Midland Basin to the north and 

east and includes the extent of Spraberry drilling to the west. Key 

input data used to assess the Spraberry Formation are listed in table 1. 

–103° –102° –101° –100°

33°

32°

31°

TEXAS

NE

W MEXICO

Odessa

Midland

Abilene

Lubbock

Hobbs

San Angelo

Big Spring

Eastern Shelf

VAL VERDE BASIN

Northern Shelf

CENTRAL BASIN

PLATFORM

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

EXPLANATION

Permian Basin Province boundary (part)

County lines

Lower Spraberry Continuous Oil Trend AU

Horseshoe atoll

Northern Spraberry Conventional Oil AU

Middle Spraberry Continuous Oil Trend AU 

0 40 80 MILES

0 40 80 KILOMETERS

TEXAS

NEW

MEXICO

Map

area

GULF

OF

MEXICO
Undiscovered Resources Summary

The USGS assessed undiscovered, technically recoverable continuous and conventional mean oil and gas resources for three AUs defined 

in the Spraberry Formation (table 2). Total estimated mean resources are 4,245 million barrels of oil (MMBO), or 4.2 billion barrels of oil, with 

an F95–F5 range from 1,873 to 7,635 MMBO; 3,112 billion cubic feet of gas (BCFG), or 3.1 trillion cubic feet of gas, with an F95–F5 range 

from 1,080 to 6,200 BCFG; and 311 million barrels of natural gas liquids (MMBNGL) with an F95–F5 range from 100 to 652 MMBNGL. 

The majority of these resource estimates are within the two continuous AUs. Mean resources of 5 MMBO with an F95–F5 range from 3 to 

10 MMBO and 3 BCFG with an F95–F5 range from 1 to 5 BCFG are attributed to the Northern Conventional Spraberry Oil AU.

Table 1. Key assessment input data for the three assessment units in the Spraberry Formation, Texas.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil. EUR, well drainage area, and success ratios are defined partly 

using U.S. shale-oil analogs. The average EUR input is the minimum, median, maximum, and calculated mean. Shading indicates not applicable]

Assessment input data Middle Spraberry Continuous Oil Trend AU Lower Spraberry Continuous Oil Trend AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 2,315,000 4,200,000 6,215,000 4,243,333 2,315,000 4,200,000 6,215,000 4,243,333

Average drainage area of wells (acres) 80 160 240 160 60 80 240 127

Success ratios (%) 80 90 95 88.3 80 90 95 88.3

Average EUR (MMBO) 0.08 0.12 0.3 0.130 0.1 0.17 0.3 0.176

AU probability 1.0 1.0

Assessment input data Northern Spraberry Conventional Oil AU

Minimum Median Maximum Calculated mean

Number of undiscovered fields 1 4 10 4.19

Sizes of undiscovered fields (MMBO) 0.5 1 10 1.27

AU probability 1.0

Table 2. Assessment results for three assessment units in the Spraberry Formation, Texas.

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

estimates. For gas accumulations, all liquids are included in the 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]

Total petroleum system 

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

Permian Basin Paleozoic Composite Total Petroleum System

Middle Spraberry Continuous Oil Trend AU 1.0 Oil 632 1,352 2,593 1,447 366 959 2,100 1,061 34 93 222 106

Lower Spraberry Continuous Oil Trend AU 1.0 Oil 1,238 2,593 5,032 2,793 713 1,841 4,095 2,048 66 180 429 205

Total undiscovered continuous resources 1,870 3,945 7,625 4,240 1,079 2,800 6,195 3,109 100 273 651 311

Northern Spraberry Conventional Oil AU 1.0 Oil 3 5 10 5 1 2 5 3 0 0 1 0

Total undiscovered conventional resources 3 5 10 5 1 2 5 3 0 0 1 0

Total undiscovered resources 1,873 3,950 7,635 4,245 1,080 2,802 6,200 3,112 100 273 652 311

References Cited

Gaswirth, S.B., Marra, K.R., Lillis, P.G., Mercier, T.J., Leathers-Miller, 

H.M., Schenk, C.J., Klett, T.R., Le, P.A., Tennyson, M.E., Hawkins, 

S.J., Brownfield, M.E., Pitman, J.K., and Finn, T.M., 2016, Assessment 

of undiscovered continuous oil resources in the Wolfcamp shale of the 

Midland Basin, Permian Basin Province, Texas, 2016: U.S. Geological 

Survey Fact Sheet 2016–3092, 4 p.

Hamlin, H.S., and Baumgardner, R.W., 2012, Wolfberry (WolfcampianLeonardian) deep-water depositional systems in the Midland Basin—

Stratigraphy, lithofacies, reservoirs, and source rocks: University of 

Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 277, 61 p.

Railroad Commission of Texas, 2014, Final order amending field rules for 

the Spraberry (trend area) field, various counties, Texas: Railroad Commission of Texas, Hearings Division, Consolidated Oil 

 and Gas Docket Nos. 7C-0291169 and 7C-0291171, 9 p., 

accessed March 1, 2017, at http://www.rrc.state.tx.us/

media/25459/7c-91169-1171afr-ord.pdf.

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.

Spraberry Formation Assessment Team

Kristen R. Marra, Stephanie B. Gaswirth, Christopher J. Schenk, Heidi M. Leathers-Miller, Timothy R. Klett, Tracey J. Mercier, 

Phuong A. Le, Marilyn E. Tennyson, Thomas M. Finn, Sarah J. Hawkins, and Michael E. Brownfield

For More Information

Assessment and methodology information can be accessed at the USGS Energy Resources Program website at https://energy.usgs.gov.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20173029