ExxonMobil in Alaska: Drilling disappointments, successes

North Slope yields discoveries, but other undeveloped basins do not show same promise

Petroleum News

Early exploration of many of the North Slope’s late 1960’s and 1970’s oil discoveries began in the mid-1960s with seismic and lease acquisition.

The first Point Thomson lease, for example, was issued in September 1965 Socony Mobil (Mobil and then ExxonMobil) and Phillips (ConocoPhillips).

The West Staines State No. 1 and No. 2 wells on that lease were completed in 1970. The discovery well would not be drilled until the mid-70s.

Point Thomson is not yet in production (see page 66), but the other three oil and gas units in northern Alaska in which ExxonMobil is currently an active partner, are in production today: They are Prudhoe Bay, discovered in 1968; Kuparuk, discovered in 1969; and Duck Island (Endicott), discovered in 1978.

The Endicott oil field, 15 miles east of Prudhoe Bay in the Beaufort Sea, would become the first offshore oil field to go into production in the U.S. Arctic.

But Exxon, Mobil and other companies would continue to explore in other basins around Alaska, all undeveloped, in the 1970s and 80s.

Basins in the Bering Sea outer continental shelf were of special interest to Mobil and Exxon, leading to an extensive effort to acquire 2D seismic data — according to the U.S. Minerals Management Service about 271,000 line miles of data were acquired between 1970 and 1985 from the Norton, St. Matthew Hall, Navarin, St. George and North Aleutian basins of the Bering Sea.

The seismic data confirmed the existence of substantial thicknesses of Tertiary strata in the basins. And large geologic structures offered enticing possibilities for petroleum traps.

Enthusiasm about the possibility of establishing a significant offshore oil province led to a series of MMS lease sales.

Between 1976 and 1983 ARCO, with funding from several companies, drilled six Continental Offshore Stratigraphic Test wells in the basins to obtain information about the basin geology.

In a flurry of activity in 1984 and 1985 several companies drilled exploration wells in the basins: Exxon drilled three wells and ARCO drilled three wells in the Norton Basin; Mobil, Exxon, ARCO, Chevron, Shell and Gulf Oil drilled nine wells in the St. George Basin; and Amoco, Exxon and ARCO drilled eight wells in the Navarin Basin.

With the exception of some promising shows onshore in the North Aleutian basin, explorers’ hopes were dashed when the companies found little or no oil potential in these basins, mainly because of a lack of suitable oil-prone source rocks.