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the USGS estimates that mean undiscovered volumes of nearly 600 million barrels of oil, about 19 trillion square feet of natural gas, and 46 million barrels of natural-gas liquids remain to be found in this area.

A map of a water inlet with labels and lines drawn on it.
A USGS assessment released in June 2011 indicates that significant natural-gas resources remain to be discovered in Cook Inlet. Yellow outline shows area evaluated for conventional oil and gas and tight gas; red outline shows area evaluated for coalbed gas. Modified from USGS Fact Sheet 2011-3068.

by Brenda Pierce and Richard G. Stanley

The U.S. Geological Survey (USGS) recently completed a new assessment of undiscovered, technically recoverable oil and gas resources in the Cook Inlet region of south-central Alaska. Using a geology-based assessment methodology, the USGS estimates that mean undiscovered volumes of nearly 600 million barrels of oil, about 19 trillion ft3 of natural gas, and 46 million barrels of natural-gas liquids remain to be found in this area. The estimates were announced on June 28, 2011.

The gas estimates are significantly more than the last USGS assessment of southern Alaska in 1995, in which a mean of 2.16 trillion ft3 of gas was estimated. This increase in the undiscovered resource is attributed to new geologic information and data and the inclusion of unconventional (or continuous) resources in the 2011 assessment.

"For the first time, USGS has evaluated unconventional as well as conventional petroleum resources in the Cook Inlet region of Alaska," said Brenda Pierce, USGS Energy Resources Program Coordinator. "The USGS conducts assessments to evaluate the nation's petroleum potential, especially as new data and information become available, in order to understand the resource endowment of the nation."

The USGS assessment is intended to provide an updated, scientifically based estimate of petroleum potential at a time of increased public concern about possible shortages of natural-gas supplies in Anchorage and nearby communities, where natural gas (methane) produced from the Cook Inlet region is the principal source of energy for heating and electric-power generation.

An offshore oil rig in the middle of the ocean with a long pipe out the side with a flame coming out.
Offshore oil-production platform in Cook Inlet.

Since oil and gas production began in the Cook Inlet region in 1958, more than 1.3 billion barrels of oil and 7.8 trillion ft3 of gas have been produced, yet the new USGS assessment shows that significant undiscovered gas remains.

This USGS assessment includes estimates of conventional and unconventional, or continuous, accumulations, including coalbed gas and tight gas formations. Coalbed gas is a form of natural gas extracted from coal seams, whereas tight gas is natural gas occurring in compact rock formations with very low permeability. Both types of gas require different production techniques than conventional gas accumulations.

The side of a cliff is a rock outcrop with a few ridges.
Outcrop of cross-laminated sandstone in the Beluga Formation west of Homer, Alaska. Where this formation occurs deep underground, it serves as a reservoir rock for natural gas.

These new estimates are for undiscovered, technically recoverable oil and gas resources, which are those quantities of oil and gas producible by using currently available technology and industry practices, regardless of economic or accessibility considerations. As such, these estimates include resources beneath both onshore and offshore areas of the Cook Inlet region (exclusive of the federal offshore) and beneath areas where accessibility may be limited by policy and regulations imposed by land managers and regulatory agencies.

The USGS worked with the Alaska Division of Geological and Geophysical Surveys and the Alaska Division of Oil and Gas to develop a geologic understanding of the Cook Inlet region. The USGS Cook Inlet assessment was undertaken as part of a nationwide project assessing domestic petroleum basins using standardized methodologies and protocols.

View the USGS Fact Sheet describing the results of the USGS Cook Inlet assessment. Learn more about this or other geologic assessments on the USGS Energy Resources Program's Web site.

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