MKRTCHYAN, OLEG M., Institute of Geology and Exploration of Combustible Fuels, Moscow, Russia

ABSTRACT: Seismo-Geological Models of Stratigraphic Sequences and Their Application to Oil and Gas Exploration in West Siberia

In west Siberia, large undrilled structural prospects for oil exploration have been exhausted. Further discoveries are expected to be made in small to medium structural traps and in lithostratigraphic traps. Prospecting and exploration for hydrocarbons in lithostratigraphic traps is based on new seismo-geological models of hydrocarbon-bearing sequences.

In middle Paleozoic rocks, small hydrocarbon accumulations have been found in structural highs; the reservoirs are composed of fractured vuggy carbonates. Seismostratigraphic criteria for prediction of such traps are uncertain.

The Lower-Middle Jurassic sequence consists of continental and partially of marine clastic rocks. The sequence is believed to contain considerable hydrocarbon resources in lithostratigraphic traps in basal sandstones and in pinch-out zones of Lower Jurassic sandstones. In the upper part of the sequence, oil pools have been discovered in channel sandstone bodies.

Two different areas of oil accumulations are found in the Callovian-Oxfordian sequence. In paleogeographic terms, these areas correspond to the nearshore zone containing some islands and to a shallow-water shelf. The upper, regressive part of the shelf contains erosional channels filled with sandstones, where both structural and lithostratigraphic traps are predicted.

The Bazhenov Formation bituminous shales of Volgian-Berriasian contain sporadically distributed fractured-porous reservoirs. Accumulations in these reservoirs are characterized by irregular oil saturation.

The Neocomian sequence consists of rocks deposited on the shallow-water shelf and on the basinal slope (clinoform). Seismo-geological data indicate that the sequence is prospective for discovery of hydrocarbons in lithostratigraphic traps. The clinoform consists of laterally prograding strata; most prospective are frontal and depocentral parts of the strata, which contain sandstone reservoirs of medium to poor quality. Lithostratigraphic traps in the shelf sequence can be found in the marginal parts of the paleoshelf, where regional pinch-out zones and sandstone lenses are common.

The Aptian-Cenomanian sequence deposited under terrestrial and coastal conditions is dominantly gas prone. New hydrocarbon discoveries in this sequence are expected in structural traps.

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