SEQUENCE STRATIGRAPHY OF YANCHANG FORMATION IN ANSAI DISTRICT
安塞地区延长组层序地层特征

By applying of sequence stratigraphy principle, connecting with the data of outcrop and core, the strata in Yanchang formation in Ansai district have been divided into S1, S2, S3 and S4. Beside the S4 which lost the highstand system tract (HST), the others possess the lowstand system tract (LST), the transgressive system tract(TST) and the HST. Every system tract is made of different stratigraphic pattern. The sequences in studying area control the assemblage of source, reservoirs and caps and the distribution of reservoirs as well as the performance of reservoirs. So Chang 7 that lie in the maximum flooding surface is the main source rock. Chang 9, Chang 4+5 and Chang 1 that lie in the TST either have the ability of producing oil or can became the caps. Chang 6, Chang 3 and Chang 2 that belong to the LST possess good reservoirs. Chang 8 lie in the LST will became the next exploration aim.