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The Study on Hydrocarbon Accumulation Regularity of Hydrocarbon-Rich Depression in Bohai Sea, China

Guo, Yonghua *1; Li, Jianping 1
(1) Bohai Oilfield Exploration and Development Institute, CNOOC Ltd. -Tianjin, Tianjin, China.

The Bohai Sea is located in the offshore exploration area of the Bohai Bay Basin. Now the most discovered large-medium oil and gas fields are mainly controlled by hydrocarbon-rich depressions.

The hydrocarbon-rich depression is referred to the depression in which excellent source rocks are widely distributed and at least one oil and gas field with hundreds of millions of reserves has been discovered, and it still has exploration potential with abundant remain resource. According to the discovered situation of hydrocarbon accumulation, there are two kinds of hydrocarbon-rich depression. One is called the common hydrocarbon-rich depression with oil and gas resource of 0.2~0.4 million tons per km square, resource scope of 500-1000 million tons and proved reserves of 200 million tons. The other is known as extremely hydrocarbon-rich depression with hydrocarbon resource of over 0.4 million tons per km square, resource scope of more than 1000 million tons and proved reserves of over 200 million tons. The Liaozhong, Bozhong and Huanghekou depressions in the Bohai offshore are belong to the latter kind.

There are three suits of excellent source rocks with TOC>1.8% and type II1 kerogen that are Lower Dongying Formation, Member 1 and Member 3 of Shahejie Formation in these depressions. Since the Neocene, those source rocks gradually reached the hydrocarbon generation and explulsion peak, which resulted in rich oil and gas resource. Member 2 of Shahejie, Dongying, and Lower Minghuazhen Formation are good reservoir-seal assemblages and important for hydrocarbon accumulation which are widely spread in these depressions. Meanwhile, Neotectonic movement in the Bohai offshore are helped the hydrocarbon generation and expulsion of source rocks and influenced hydrocarbon accumulation and redistribution in various kinds of traps. Tan-Lu strike-slip fault and its derivative fractures also played the important role of superior hydrocarbon carrier and accumulation system. So the multiple favorable factors of hydrocarbon accumulation can be coupled very well in these depressions. This is why the Neocene large-scale hydrocarbon accumulation formed in the Bohai offshore area, such as PL19-3 oilfield is located on the belt of Tan-Lu strike-slip faults, the huge oil reservoirs forming get exactly benefit from rich sources of Bozhong depression and the superiority of oil-gas gathering by Tan-Lu strike-slip faults, etc. Moreover, by factors such as Tan-Lu fault and deposition rate of the depressions, the above three depressions also have their own oil and gas fields with specific geological characteristics and differ in depression structures, source rocks thermal evolution, hydrocarbon accumulation, and so on.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California