Abstract: Sedimentary Style and Oil-Gas Field Distribution in Western Bohai Bay

Hansheng Qiao

Western Bohai Bay is located near Tianjing City and the Yanshan Mountains. Tectonically, it is part of the Bohai Bay rift, including the Qiku, Nanpu, and Cangdong depressions. The Paleogene strata consist of three cycles in the rift. Usually, the sublacustrine fans or basalts formed at the initial stage of every cycle. The dark shales and turbidites developed at the high level of lacustrine transgression. However, the deltas or evaporates appeared at the regressive stage. The sublacustrine fans or deltas generally distribute in the marginal part of a depression, with humic type kerogen. The dark shales of deep lacustrine facies in the inner part of it contain sapropel type kerogen. The transitional zone between them is interbedded shales and sandstones, with mixed type kerogen. The oi -gas fields mainly occur in the transitional zone around the oil-generating center. The great oil-gas fields are formed in areas where the big drape anticline coincided with the sublacustrine fan-front or delta-front sandstones and were sealed by shales or evaporates. A great number of small overpressured oil reservoirs are in the mature source rocks in the depression center.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994