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ABSTRACT: The Petroleum Basins of the Northwest Pacific

Igor Khvedtchuk

The northwest Pacific area includes the major petroleum basins flanking the Pacific Ocean in Asia (Japanese, Isikury-West Sakhalin, North Sakhalin, West Kamchatka, Khatyrskiy, and Anadyrskiy).

The petroleum basins consist of Tertiary cover (marine, coastal, and continental terrigeneous, siliceous volcanogenic, and volcanogenic-sedimentary rocks) and pre-Genozoic basement composed of geosyncline rock associations. Sediment thickness of the basins attains 10-12 km. Northwest and northeast faults control graben feature in the basement and develop rift systems. The general thickness of the Earth's crust is 27-31 km. All petroleum basins are connected with rifts. Rifting influenced the volcanic and magmatic activity, the abnormally high temperature and pressure in oil- and gas-bearing filling of basins.

Analysis of data shows that the main factors affecting deposition of the source rocks and their spatial distribution and effectiveness in generating hydrocarbon reserves are geological age, regional tectonics, paleography, dominant kerogen type, and temperature.

There are various types of petroleum source rocks: upper Eocene marine shales (Khatyrskiy basin), kerogen type III; upper Oligocene siliceous shales (North Sakhalin, Japanese, West Kamchatka and Anadyrskiy basins), kerogen type II and III; and middle Miocene marine shales (Japanese, Isikury-West Sakhalin and North Sakhalin basins), kerogen type II. The quantity of organic matter in source rocks is 0.6-3.4% and the geothermal gradient is 24-44°C/km.

The main reservoirs are Miocene-lower Pliocene sandstones, upper Miocene deltaic sandstones, and upper Oligocene-lower Miocene siliceous shales. Oil and gas accumulated in anticline structures and stratigraphic traps.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990