Abstract

The Swanson River oil field was discovered in 1957 by Richfield Oil Corporation with the drilling of the Swanson River Unit No. 1 well. The timing and significance of this discovery sparked an Alaskan industry and demonstrated the territory’s ability to develop its own mineral resources and helped pave the way to Alaskan statehood in 1959.

Both oil and gas are produced from nonmarine reservoirs of the Tertiary Kenai Group, which are considered to be primarily fluvial in nature with the structural trapping component of a westerly verging, asymmetric anticline. The Oligocene-aged Hemlock Formation is composed primarily of conglomerates and sandstones, while the overlying Miocene Tyonek and Beluga Formations consist of siltstones and sandstones. Coals are present throughout the Tyonek and Beluga, although they are thicker and more laterally continuous in the Tyonek. The gas-prone Miocene- and Pliocene-aged Sterling Formation is characterized by thick stacks of laterally extensive fluvial sandstones with little coal or shale.

Oil and thermogenic gas from the Hemlock Formation and the G-Zone of the lower Tyonek Formation represent the vast majority of cumulative production at Swanson River (435 MMBOOIP, 230 MMBO CUM production). The organic-rich shales and siltstones of the middle Jurassic Tuxedni Group serve as the source rock for oil and associated gas production from the Hemlock and Tyonek G-Zone. Biogenic gas of the Tyonek, Beluga, and Sterling Formations is derived from numerous coals and carbonaceous siliciclastics interbedded within these sandstone reservoirs (52 BCF CUM shallow gas production).

Development of the Swanson River field has progressed through a number of stages. The initial development phase of Hemlock oil (1957–1962) was supplemented by a gas pressure maintenance program from 1962 to 1998. Peak production of 38,000 BOPD was reached in 1966 with the onset of full-field compression, and current field production is 600 BOPD and 2.5 MMCFD of natural gas from 21 active wells. Along with continued delineation of Miocene-aged gas reservoirs, development of lower Tyonek G-Zone oil and production of Hemlock blowdown gas began in the mid-1990s and continues through the present. In 2001, gas storage operations were implemented along with ongoing oil and gas production, allowing Swanson River to continue playing a significant role in meeting the increasing demand for gas in the Cook Inlet area.

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