The North Cook Inlet Tertiary System Gas Pool lies offshore on the western side of the Cook Inlet, 5 miles from the western coastline of Cook Inlet and about 37 miles west-southwest of Anchorage. This pool was discovered by the Pan Am Cook Inlet State 17589 No. 1 exploratory well in 1962, which blew out on August 23, 1962 and burned, producing a flame that was visible from Anchorage until the well was finally killed on October 23, 1963. A Drill Stem Test of the relief well in the interval that blew out indicates a pressure of about 13.5 ppg equivalent mud weight. At the time of the blowout, 11.6 ppg mud was being used to drill the well. The pool was subsequently delineated by six additional exploratory wells drilled between 1962 and 1966 and found to encompass about 8,000 acres.

This large pool has been developed from the Tyonek Platform using a "cluster" spacing pattern rather than standard 640-acre spacing, as prescribed by Commission regulations. At the time of initial development, the operator testified that cluster spacing would efficiently and economically drain the entire reservoir from a single platform, achieving greater initial deliverability than expected from wells located on a regular pattern at the center of their respective governmental sections. The Tyonek Platform, the 12th platform in the Cook Inlet, was installed in about 100' of water during 1968. This platform is designed to withstand the harshest expected conditions: 80 mph winds, 27’ waves, -40° F, and the impacts of 1500 ton ice floes moving at 10 feet per second.

Production from the North Cook Inlet Tertiary System Gas Pool began in 1969. The liquefied natural gas (LNG) facility at Nikiski was built to make use of this gas. The facility began operations during 1969 based on long-term contracts with Tokyo Electric Power Co. Inc., and Tokyo Gas Co. Ltd. Although this pool was expected to supply the market for only 20 to 30 years, production continues today from the Sterling and Beluga Formations. Daily production from March 1994 to March 2003 averaged about 145 million cubic feet per day. Since then, production has declined to an average of 43.7 million cubic feet per day for the first half of 2011.

In 2004, a Department of Energy study estimated that the remaining proved reserve for the two fields supplying natural gas for the LNG facility, Kenai and North Cook Inlet, would not be sufficient to continue LNG sales beyond 2009. In April 2009, the volume of shipments was cut when the tanker fleet was reduced by half. Current plans are to mothball the LNG facility during August 2011, leaving it available for possible future use. ConocoPhillips reportedly plans to continue operating the Tyonek Platform to meet local gas demands.

The North Cook Inlet Tertiary System Gas Pool is defined as the interval that correlates to the interval from 3,500' to 6,200' measured depth in the Pan American Petroleum Corporation Cook Inlet State 17589 No. 1 well. The structure at North Cook Inlet, as defined by subsurface well control and seismic data, is a northeast-trending anticline that measures about 5-3/4 miles long and 3 miles at its widest point.

The producing intervals are the Sterling Formation (about 350' of net pay) and Beluga Formation (about 160' of net pay). The Pliocene-aged Sterling Formation is composed of coarse-grained clastic intervals and interbedded thin carbonaceous mudstones and has a high net-to-gross sand ratio. The Miocene-aged Beluga Formation is composed of mudstone, siltstone, coal and sandstone and has a low net-to-gross sand ratio. The sandstone layers in the Sterling and Beluga Formations are channel belt and crevasse-splay deposits. Well logs indicate that the productive sand members have porosity ranging from 22 to 36% (28% average), permeability averaging about 180 millidarcies, and water saturation averaging about 40%.

Current exploration activities in the North Cook Inlet area are seeking untapped channel sands and have reportedly identified a possible “faulted structural nose” to north of the field with potential reservoirs in the Beluga and Tyonek Formations.