ABSTRACT: Petroleum Geology of Sakhalin Island, USSR
Matthew R. Silverman
Sakhalin is a long, narrow island approximately the size of Hokkaido, consisting of two coastal mountain ranges and a central valley. It is located 10-300 km (6-190 mi) east of the Soviet mainland in the Sea of Okhotsk. The island is cored by Cretaceous and older rocks that comprise a fold belt characteristic of plate collision and accretion tectonics. Cenozoic deformation has produced numerous asymmetric compressional anticlines, many of which produce oil and gas.
Reservoirs are primarily Miocene and Pliocene fluvial and deltaic sandstones, related to the paleo-Amur river. Oil is also being produced from fractured diatomites similar to California's Monterey formation. Most fields have numerous stacked pay zones. Source rocks and seals are deltaic and marine shales. Production is limited to several troughs of folded Tertiary sediments; the most important basins in terms of hydrocarbon production and potential are the North Sakhalin basin, the Pogranich graben, the Terpeniya basin, and the Aniva gulf.
Significant production has been established in the North Sakhalin basin since the 1920s, but reserves in the other basins are minor. Sakhalin has produced 400 to 600 MMBO and 0.5 to 1.2 tcfg from over 60 fields, most of which are onshore. As the Soviet Union's only secure source of petroleum in the Far East, Sakhalin's reserves have a strategic importance far exceeding their market value.
Current oil production rate is 17-18 MMBO/year. A gas pipeline connecting Sakhalin with the Soviet mainland was completed in 1987 and is expected to boost gas output to 100 bcfg/year by 1990. The largest fields are located on Sakhalin's NE coast and include Okha (200 MMBO, onshore) and recently discovered Chayvo (240 MMBO and 4.2 tcfg, offshore).
Sakhalin's greatest hydrocarbon potential lies offshore, where exploration is less mature. Relatively large, gently folded offshore structures in the North Sakhalin basin have been mapped. Marine and deltaic source rocks and reservoirs are present at favorable drilling depths. Significant future oil reserves will come largely from the offshore portion of the North Sakhalin basin. The Terpeniya basin and Aniva gulf have substantial gas prospects and are close to the Japanese market. The Soviets have recognized that foreign capital and technology will be required to exploit these resources.
A current joint venture between several Japanese companies and the Soviets, SODECO, has produced disappointing results to date. Explanations include the brief offshore drilling season, unfavorable legislation, bureaucratic red tape, and concentration on convenient (but smaller) structures. The development of Chayvo field has dominated the limited offshore drilling capabilities of the Soviet Pacific fleet, at the expense of true exploration.
Moscow indicated recently that the Soviets plan to improve the present joint venture laws to create broadly capitalist economic zones. Anticipated changes include radical reforms concerning wholly owned subsidiaries, convertible currency, foreign executives, and repatriation of profits.
AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990