Sequence stratigraphic characteristics of Triassic Yanchang formation in Fuxian-Huangling area of Ordos basin

By applying the principles and methods of sequence stratigraphy, combined with comprehensive data analysis of outcrops, drilling and logging, the types of sequence boundary of Triassic Yanchang formation in FuxianHuangling area can be identified by logging signs. The sedimentary evolution of Triassic experienced 5 times of lacustrine transgression and lacustrine regression, which had a long period and a large scale. There were 5 obvious flooding surfaces and 6 sequence interfaces could be identified. According to the information, the Triassic can be divided into 5 long-term and 14 middle-term sequence cycles. Based on the sequence classification of single wells and the correlation in well-tie sections, it is the Triassic sequence stratigraphic framework of Fuxian-Huangling area that can be established. It is analyzed that the symmetry of sequence structure has obvious regularity along with the evolution of the lake basin. The strata distribution is significantly affected by two directions of provenances including northeast and southwest, which is characterized by large formation thickness in the main provenance area and relatively small thickness in the other areas. According to the characteristics analysis of source-reservoir-cap rock assemblages within sequence framework, there are 4 sets of obvious source-reservoircap rock assemblages, which controls the distribution of oil and gas of Yanchang formation in Fuxian-Huangling area.