层序单元体系域划分及勘探意义

体系域是层序地层学理论体系中的重要概念，在隐蔽油气藏的勘探中，勘探家们极为重视低位体系域。但体系域的成因意义、是否有不同级别层序的体系域以及如何划分，在实际工作中认识不一致。结合勃海湾盆地的勘探实例，分析体系域的成因机制、组合特征和勘探规律，认为：体系域是基准面变化等因素作用的产物，不同级别的层序都发育着与其对应的体系域：一般情况下，三级层序对应的体系域单元与含油气层的规模相匹配，但四级层序对应的体系域才是隐蔽油气藏赋存的有利部位。图5参6。

Division of system tract of different sequence units and its implication in petroleum explo-ration

Generally, explorationists are interested in lowstand system tract in the exploration of subtle traps. However, system tracts of different levels and their formation need to be further studied in exploration practice. The formation of system tracts, their combination characteristics and application in hydrocarbon exploration, as well as the case studies of the Bohai Bay Basin, were studied in this paper. From the results, it was obtained that system tracts were the products of datum plane variation, and system tracts developed in sequences of different grades. The system tract units of Grade Three are corresponding to oil gas bearing layers. However, oil gas is actually accumulated in system tracts of Grade Four.