U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2014–3033

April 2014

Assessment of Potential Unconventional Lacustrine Shale-Oil and 

Shale-Gas Resources, Phitsanulok Basin, Thailand, 2014

Introduction

The U.S. Geological Survey (USGS) assesses the potential for 

technically recoverable unconventional shale-oil, shale-gas, tightoil, tight-gas, and coal-bed gas accumulations in priority geologic 

provinces worldwide. This report summarizes the geologic model 

and assessment of potential shale-oil and shale-gas resources of 

the Phitsanulok Basin, one of the largest of the Cenozoic extensional basins within onshore Thailand (fig. 1). The Phitsanulok 

Basin contains the Miocene Chum Saeng Formation petroleum 

system described in detail by Pinyo (2011). Geologic data depicted 

in a series of maps by Pinyo (2011) permit a unique opportunity 

to define assessment units and to assess potential unconventional 

shale-oil and shale-gas resources within a well-defined lacustrine 

petroleum system.

Geologic Definition of Assessment Units

Assessment units (AUs) within unconventional accumulations 

are defined by the USGS using a set of geologic screening criteria 

based on well-known U.S. accumulations. The most viable shalegas and shale-oil accumulations in the United States exhibit total 

organic carbon (TOC) values greater than 2 weight percent, contain 

predominantly Type I or Type II kerogen, are overpressured, 

reflect tens of meters of organic-rich shale source rock, and occur 

at depths necessary to retain adequate reservoir pressure. Thermal 

maturity values (as measured by vitrinite reflectance, Ro

) between 

0.55 to 1.1 percent Ro characterize potential shale-oil reservoirs, 

and Ro

 values greater than about 1.1 percent characterize potential 

shale-gas reservoirs. These geologic criteria, when applied to the 

data mapped by Pinyo (2011), allowed definition of the Phitsanulok Basin Shale Oil AU and the Phitsanulok Basin Shale Gas 

AU within the Synrift Lacustrine Total Petroleum System of the 

Miocene Chum Saeng Formation.

Geologic Model for Assessment

The geologic model used in assessment of the Miocene Chum 

Saeng Formation of the Phitsanulok Basin assumes oil and gas 

were generated within organic-rich (greater than 2 weight percent 

TOC), thick (greater than 15 meters), thermally mature (more than 

0.55 percent Ro

), overpressured (greater than 0.45 pounds per square 

inch per foot, psi/ft) lacustrine shales. The geologic model further 

assumes that recoverable oil and gas remain in the matrix of the 

source rock, even with known migration of oil from source rocks 

of the Chum Saeng Formation into several updip conventional oil 

fields, including Sirikit Field (Flint and others, 1988). Although 

recoverable shale oil has not been reported from the source rock, 

recoverable shale gas was tested from Chum Saeng source rock 

(Pinyo, 2011). Geologic and production analogs for lacustrine 

shale-oil and shale-gas reservoirs are quite limited from the United 

States, but recent drilling and production data from thermally 

mature lacustrine shales within the Eocene Green River Formation in the Uinta Basin, Utah, were used as partial geologic and 

estimated ultimate recovery (EUR) analogs. Other U.S. analog data 

were used to model drainage areas of wells and well success ratios. 

Key assessment input data are summarized in table 1. Uncertainty 

with respect to quantities of recoverable oil and gas in the Chum 

Saeng source rock led to modeled geologic probabilities of 0.90 for 

the Phitsanulok Shale Oil AU and 0.95 for the Phitsanulok Shale 

Gas AU (table 2).

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

recoverable mean resources of 53 million barrels of shale oil and 320 billion cubic feet of shale gas in the 

Phitsanulok Basin, onshore Thailand. 

GULF OF 

THAILAND

ANDAMAN

SEA

THAILAND

BURMA

CAMBODIA

LAOS

98° 100° 102° 104°

20°

18°

16°

14°

12°

10°

0 125 KILOMETERS

0 125 MILES

AUSTRALIA

CHINA

INDIA

Indian 

Ocean

Area

of

figure

Petchabun

Petchabun

Basin

Tak

Mae

 Sot

 Basin

 Fang

Basin

 Chiang

 Mai

 Basin

Chiang Mai

Bangkok

Uttaradit

Phitsanulok

Phitsanulok

Basin

Phitsanulok Basin

Cenozoic basins

EXPLANATION

Figure 1. Locations of the Phitsanulok Basin and other Cenozoic 

basins in northern Thailand. Modified from Morley and others (2001).

National and Global Petroleum Assessment
Unconventional Resource Summary

The USGS assessed potential technically recoverable shale-oil

and shale-gas resources in the Phitsanulok Basin of Thailand, 

resulting in total estimated mean resources of 53 million barrels of 

oil (MMBO), 320 billion cubic feet of gas (BCFG), and 5 million 

barrels of natural gas liquids (MMBNGL) (table 2). The ranges 

of resource estimates (0 to 98 MMBO; 0 to 622 BCFG; 0 to 

10 MMBNGL) reflect considerable geologic uncertainty in these 

unconventional assessment units, particularly with respect to quantities of petroleum potentially remaining in the Chum Saeng Formation source rock.

The Phitsanulok Basin represents one of the largest in a series 

of geologically complex Cenozoic-age extensional basins within 

onshore Thailand (Morley and others, 2001; Morley, 2009). Several 

other Cenozoic extensional basins, such as the Fang, Chiang Mai, 

Mae Sot, Petchabun, Suphan Buri, and Ayutthaya Basins, may also 

contain potential shale-oil or shale-gas resources, but geologic and 

production-test data are not yet available with which to complete a 

quantitative assessment.

For Further Information

Assessment results also are available at the USGS Energy 

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

References

Flint, Stephen, Stewart, D.J., Hyde, T., Gevers, E.C.A., Dubrule, 

O.R.F., and van Riessen, E.D., 1988, Aspects of reservoir geology and production behavior of Sirikit oil field, Thailand—An 

integrated approach: American Association of Petroleum Geologists Bulletin, v. 72, no. 7, p. 1254–1269.

Morley, C.K., 2009, Evolution from an oblique subduction backarc mobile belt to a highly oblique collisional margin—The 

Cenozoic tectonic development of Thailand and eastern Myanmar, in Cawood, P.A., and Kroner, A., eds., Earth accretionary 

systems in space and time: Geological Society of London Special Publication, no. 318, p. 373–403.

Morley, C.K., Woganan, N., Sankumarn, N., Hoon, T.B., Alief, A., 

and Simmons, M., 2001, Late Oligocene–Recent stress evolution 

in rift basins of northern and central Thailand—Implications for 

escape tectonics: Tectonophysics, v. 334, p. 115–150.

Pinyo, Komon, 2011, Unconventional petroleum system evaluation 

of the Chum Saeng Formation, Phitsanulok Basin, Thailand, 

in International Conference on Geology, Geotechnology, and 

Mineral Resources of Indochina [GEOINDO]: 11th Conference 

Proceedings, Khon Kaen University, Department of Geotechnology, Khon Kaen, Thailand, December 1–3, 2011, p. 267–280.

Assessment input data

Phitsanulok Basin Shale Oil AU

mean

Potential production area of AU (acres)

Average drainage area of wells (acres)

Average EUR (BCF, gas; MMB, oil)

Success ratios (%)

Phitsanulok Fact sheet table1.indd

Table 1. Key assessment input data for shale-oil and shale-gas assessment units for the Phitsanulok Basin, onshore Thailand. 

[Estimated ultimate recovery (EUR) per well, well drainage areas, and well success ratios are taken from U.S. shale-gas and shale-oil analogs. 

The EUR input includes the minimum, median, maximum, and calculated means of the average EUR Abbreviations: BCF, billion cubic feet; 

MMB, million barrels; AU, assessment unit] 

mean

Mode Maximum Calculated Mode Maximum Calculated 

 Phitsanulok Basin Shale Gas AU

80

100,000 205,000 250,000 185,000 10,000 173,000 200,000 127,667

80 120 160 120 100 140 180 140

0.05 0.08 0.12 0.08 0.3 0.7 1.0 0.71

10 50 47 10 50 80 47

Minimum Minimum

Total petroleum system 

(TPS) 

and assessment units (AUs)

AU 

probability

Field 

type

Total undiscovered resources

Synrift Lacustrine TPS

Phitsanulok Basin Shale Oil AU 

Phitsanulok Basin Shale Gas AU 

Total unconventional

 resources

Table 2. Shale-oil and shale-gas assessment results from Phitsanulok Basin, Thailand. 

[Results shown are fully risked estimates. For gas accumulations, all liquids are included as natural gas liquids. Total undiscovered gas resources are the sum of 

nonassociated gas (that is, gas-in-gas accumulations) and associated gas (gas-in-oil accumulations). The notation “F95” represents a 95-percent chance of at least 

the tabulated amount being present; other fractiles are defined similarly. Fractiles are additive under the assumption of perfect positive correlation. Gray shading

indicates “not applicable.” Abbreviations: MMBO, million barrels of oil; BCFG, billions of cubic feet of gas; MMBNGL, million barrels of natural gas liquids; 

TPS, total petroleum system; AU, assessment unit; NGL, natural gas liquids] 

Gas (BCFG)

0 54 98 53 0 31 63 32 0 1 1 1

0 278 559 288 0 4 9 4

0 54 98 53 0 309 622 320 0 105 5

0.90 Oil

0.95 Gas

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

Oil (MMBO) NGL (MMBNGL)

Phitsanulok Basin Assessment Team

Christopher J. Schenk, Ronald R. Charpentier, Timothy R. 

Klett, Tracey J. Mercier, Marilyn E. Tennyson, Janet K. Pitman, 

and Michael E. Brownfield.

ISSN 2327-6916 (print)

ISSN 2327-6932 (online)

http://dx.doi.org/10.3133/fs20143033