Abstract:

In many hydrocarbon basins of the Early Eogene in East China,oil and gaspools have the regularity of ring or semi-ring distribution arround the center ofthe depressions. This is determined by the basic evolution regularity or contem-poraneous fualt-depression. Analyzed the seismic sequence of a typical half-basinin the Bohai Bay Basin, the author suggests that: 1.The evolution process of 4 contemporaneous fault-depression involved sever-al fault-depressed cycles and the rising-dropping periods of water-level. Themain reason that caused the water-level of a inland lacustrine basin to vary wasthe fault subsidence of boundary faults and the aggradation of sediments.Fault-subsidences of rhythmical pulse in association with cyclic wave sedimenta-tion happened througbout tke whole evolution process of the basin. That is tosay, so-called contemporaneous fault-depression basin is composed of several un-contemporaneous stages, and compensation basin is alternatively composed ofmany stages of un-compensation and super-compensation. 2.Each cycle or period of this kind of basin's evolution process included threestages such as fault-depressed, cut-filled and stable deposited stages. These stagesdiffered from one another in dynamic and paleogeography. They controlled thedistribution of traps and reservoirs. In the ring belt closing to depressioncenter, the types are the most varied. 3.Each hydrocarbon basin or depression can be divided into three oil and gasbelts such as central source belt, accumulation ring belt and the surroundingescape belt. Each belt has different pools. Among these belts, the accumulationring belt is the most favourable one. As boundary conditions are different, the ring belts are also varied. They can be subdivided into four kinds as be-low: 1.semiring-Banqiao type; 2. single ring-Baxian type; 3. double-ring-Dong-ying type and 4.multi-ring-Xingang type. It is mostly possible to form hugeoil and gas provinces in the places where two or more ring belts overlapped.4. According to the above version, the guide ideology of oil and gas explora-tion should be ridded from the idea of the secondary tectonic zones which havebeen used for more than 20 years in exploration in East China, and depres-sion should be taken as the basic exploratian unit and research target.