Assessment of potential unconventional lacustrine shale-oil and shale-gas resources, Phitsanulok Basin, Thailand, 2014

National and Global Petroleum Assessment

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.

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.

Figure 1. Locations of the Phitsanulok Basin and other Cenozoic basins in northern Thailand. Modified from Morley and others (2001).

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 shale-gas 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).

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.

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.

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.

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