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New Estimates of Undiscovered Oil and Gas Resources in the Cook Inlet Region, South-Central Alaska

Stanley, Richard G.*1; Charpentier, Ronald R.2; Cook, Troy A.2; Houseknecht, David W.3; Klett, Timothy R.2; Lewis, Kristen A.2; Lillis, Paul G.2; Nelson, Philip H.2; Phillips, Jeffrey D.2; Pollastro, Richard M.2; Potter, Christopher J.2; Rouse, William A.3; Saltus, Richard W.2; Schenk, Christopher J.2; Shah, Anjana K.2; Valin, Zenon C.1
(1) U.S. Geological Survey, Menlo Park, CA.
(2) U.S. Geological Survey, Denver, CO.
(3) U.S. Geological Survey, Reston, VA.

The U.S. Geological Survey (USGS) recently reassessed the undiscovered petroleum potential of the Cook Inlet region, a partially explored petroleum province from which about 1,330 million barrels of oil (MMBO) and 7,898 billion cubic feet of natural gas (BCFG) have been produced since 1958. The USGS estimates that undiscovered, technically recoverable volumes of oil in the Cook Inlet region range from 108 to 1,359 MMBO with a mean estimate of nearly 600 MMBO and that undiscovered, technically recoverable volumes of gas range from 4,976 to 39,737 BCFG with a mean estimate of about 19,000 BCFG. There is a 95% probability of recovering more than the lower number in these ranges, and a 5% probability of recovering more than the higher number.

The USGS assessment used methodologies that are based on petroleum systems and assessment units (AU) and have been applied to previous USGS assessments elsewhere in the United States. In the Cook Inlet region, the USGS defined 3 Total Petroleum Systems and 4 AU within them. All of the forecasted oil resources and about 72% of the mean natural gas estimate are expected to be found in conventional accumulations in the Tertiary Sandstone Oil and Gas AU and the Mesozoic Sandstone Oil and Gas AU. About 25% of the mean natural gas estimate is expected in unconventional (continuous) accumulations in the Cook Inlet Coalbed Gas AU, whereas 3% of the mean natural gas estimate is expected in unconventional accumulations in the Tuxedni-Naknek Continuous Gas AU. The area assessed includes onshore and the State offshore but not the Federal offshore.

The new USGS estimates provide an updated, scientifically-based forecast of petroleum potential at a time of increased concerns over possible supply shortages of natural gas in the Anchorage metropolitan area, where natural gas is the principal source of energy for heating and electric power generation. Since the previous USGS assessment in 1995, the Cook Inlet region has seen a modest renewal of exploration activity, mainly by smaller companies. The USGS assessment was conducted in close cooperation with the State of Alaska and benefited from new data provided by field-based studies of Tertiary and Mesozoic depositional systems, surface and subsurface geologic mapping, seismic interpretation, gravity and magnetics modeling, review of organic geochemical data from oils and source rocks, modeling of the timing of oil generation, and studies of sedimentary petrology and reservoir quality.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California