KHVEDCHUK, IGOR, Oil and Gas Research Institute, Moscow, Russia

ABSTRACT: The Petroleum Basins of the Sea of Okhotsk

The Okhotsk area includes the major oil and gas basins of north Sakhalin and west Kamchatka, where more than 70 fields have been discovered. The basins consist of Tertiary cover (marine, coastal and continental terrigenous, and siliceous volcanogenic and volcanoclastic rocks) and pre-Cenozoic basement composed of geosynclinal rock associations. Sediment thickness in the basins attains 10-12 km. Rifting of the basement has resulted in the development of grabens controlled by northwest- and northeast-trending faults. Crustal thickness is 27-31 km. All the petroleum basins are related to rifts, which were associated with volcanic and magmatic activity and abnormally high temperature and pressures.

Analysis of the data show that the main factors affecting deposition of the source rocks, their spatial distribution, and their effectiveness in generating hydrocarbons are the geological age, regional tectonics, paleogeography, dominant kerogen type, and temperature. There are various types of oil and gas source rocks: Paleocene to lower Eocene claystones contain gas-prone kerogen type III (west Kamchatka); upper Eocene and Oligocene marine clays and siliceous clays contain oil-prone kerogen type II (west Kamchatka); upper Oligocene to lower Miocene siliceous shales (north Sakhalin and west Kamchatka) contain kerogen type II; lower and middle Miocene clays are gas prone (north Sakhalin and west Kamchatka); and middle Miocene marine clays contain oil-prone kerogen type II (north Sakha in). The quantity of organic matter in the source rocks ranges from 0. 6 to 4.2%, and the geothermal gradient ranges from 24 to 44 degrees C per km.

The main reservoirs are upper Oligocene-lower Miocene siliceous shales, Miocene-lower Pliocene sandstones, and upper Miocene deltaic sandstones. Oil and gas accumulations occur in anticlines and stratigraphic traps.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.