Production from the Middle Kenai Gas Pool began in December
1968 from the Grayling Platform, followed shortly thereafter by production
from the Dolly Varden and King Salmon Platforms. The initial production consisted
of "wet" gas, which contains appreciable amounts of natural gas liquids produced
in association with oil from the West Foreland, Hemlock and Middle Kenai G
oil pools. Most of the associated gas produced from McArthur River prior to
1988 was not sold commercially; it was used to fuel lease operations and provide
gas lift. In 1988, the Steelhead Platform was constructed to produce dry
gas (methane) from the Grayling Gas Sands. Production from the pool peaked
at 225 billion cubic feet per day in November 1997. During December 2004, production
from the platform averaged 92.5 million cubic feet per day. About 4% of the
gas from this pool is now used for lease operations, and the remainder is sold
The Middle Kenai Gas Pool is defined as the accumulation of gas common to, and correlative with, the accumulation found in the Marathon Trading Bay Unit wells between the measured depths of 1,518 in well M-1 to 8,982 in well M-14. The Middle Kenai Gas Pool (also known as Grayling Gas Sands) is located within the Upper Middle Miocene Chuitna and Middle Ground Shoal members of the Tyonek Formation, which are part of the Kenai Group. The reservoir sands occur in a continuous sequence that contains the gas accumulations. As currently defined, the Middle Kenai Gas Pool consists of the Upper A series, Zones A through F, and the G-O series, which lies above the G Zone Oil Pool.
In the vicinity of the Steelhead Platform, the non-marine sediments of the Middle Kenai Gas Pool were deposited in fluvial-alluvial meander belts. The sand/shale sequences within this portion of the Tyonek Formation are interbedded with distinctive coal layers, suggesting low energy, swamp-like conditions. Sand units are often conglomeratic, generally thin (20 to 50 feet thick), and may not persist laterally. Porosity ranges from 12 to 32 percent. The McArthur River Field structure is an asymmetric anticline that is oriented approximately north 20° east. The structure is cut by two normal faults that do not affect the limits of the hydrocarbon reservoirs.
McArthur River original gas in place is estimated to be 1.35 TCF.