Petroleum Generation And Accumulation Patten In The Yangxin Depression

The Yangxin Depression is located at the northern-west part of the Huimin Depression, Bohaiwan Basin. It is a typical fault-folded depression, characterized by wide distribution of petroleums, multi-types of oils and gases, and complicated structures. Since there have been lack of detailed research on petroleum generation and accumulation patterns of this depression for a long period, there is now no a clear idea for its petroleum potential and further exploration direction. In this study, a combined method of petroleum generation kinetics with petroleum system has been applied to investigate the petroleum generation of source rocks and petroleum pool formation of this depression, and the following main results have been obtained:(1) The petroleum generation of the ES₄ source rocks in the Yangxin Depression began from 38Ma, and has being lasted to the present. There ware two peak stages of petroleum generation. The first peak occurred during 30-20Ma, related to ES₄ source rocks from the depression center, and the second peak was after 10Ma,and originated from ES₃ and ES₄ source rocks in the depression.(2) The petroleum generation patterns of different types of source rocks have been suggested. It has been found that the ES4 source rock is characterized by an earlier oil generation and a lower maturity of oil window, with a VRo range of 0.48-0.90%, which is believed to be related to its kerogen with a dominant maceral of degraded-amorphinite and a sulfur -rich element composition.(3) It has been recognized that there are two types of petroleum reservoir and three kinds of petroleum pool formation pattern in the Yangxin Depression. The petroleum reservoirs are sandstone reservoir and igneous rock reservoir, and the formation patterns include structural trap, structural-lithological trap and lithological trap. The vertical distribution of petroleum pools show an alteration of matured oils, low mature oils and biogases from ES₄, ES₃ to ES₁ strata. The petroleum migration was mainly lateral and most of the petroleum pools was self-generation and self-store.(4) Seven exploration targets for ES₄-ES₃ strata and two exploration blocks for ES₁ strata has been evaluated, and a oil resource of 2810×10⁴t and a biogas resource of 43.5×10⁸m³ were protested.These above results not only give a guide to the petroleum evaluation and exploration in the Yangxin Depression, but also provide a case study on petroleum generation and accumulation for other depressions in the Shangli Oilfield.