Bulletin of the Geological Society of Malaysia, Volume 37, July 1995, pp. 485 -489
Research Institute of Petroleum Exploration and Development, CNPC, Xue Yuan Lu 20, Beijing, China
Abstract: The western Bohai Bay is tectonically part of the Bohai Bay Rift System, and includes the Qiku, Nanpu and Cangdong Depressions. Paleogene rift strata consist of three cycles. 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 are generally distributed in the marginal part of a depression with humic type kerogen. The dark shales of deep lacustrine facies are located in the inner part containing sapropel type kerogen. The transitional zone consists of interbedded shales and sandstones, with mixed-type kerogen. The major oil and gas fields occur in the transitional zone, around the oil-generating “kitchen”. The great oil and gas fields are formed in the areas where big drape anticlines are coincident with sublacustrine fan front or delta front sandstones and are sealed by shales or evaporites. Numbers of small overpressured oil reservoirs are subtley expressed in the mature source rocks in the depression center.