Analysis Of High-Resolution Sequence Stratigraphy Of Shallow-water Deltas In Interval 8 Of Yanchang Formation, Jiyuan Area Of Ordos Basin

Jiyuan area is located in the southwest of Ordos Basin. Interval 8 of Yanchang Formation of the Upper Triassic is target stratum of exploration activity. Recently, gas/oil has been drilled in the layer in study area, But they are mainly low-yielding wells, it is mainly related with sandstone thickness varies greatly, spatial distribution and strong heterogeneity, and low permeability sandstones reservoirs which are low oil saturation Interval 8 of Yanchang Formation. Therefore, Provenance analysis and sedimentary facies of Interval 8 of Yanchang Formation are studied. The research has acquired following results:1. Based on the core observation, analysis of logging and debris and minerals data, and combined with the fruit of predecessors this paper points out for the first time that the Interval 8 of Yanchang Formation in Jiyuan area in Ordos Basin developed shallow water delta.2. Provenance analysis through heavy mineral and sedimentology Etc, the sedimentation in the study area was controlled by the northeast, northwest and southwest sources, and the three material properties of the source rock area are identified. The extension direction of the three main source area of the Interval 8 of Yanchang Formation is also the extension direction of the reservoir, and it controls the development size of the sand body.3.With the theory of high-resolution sequence stratigraphy, the base-level cycles in chang-8 oil set of Yanchang formation in Jiyuan area of Ordos Basin are recognized as 2 middle-term cyclic sequences(MSC1 and MSC2) and 6 short-term cyclic sequences(ssc1-ssc6). Distribution, structure and stacking pattern correlation of sequence of Interval 8 of Yanchang Formation in Jiyuan area have been described,and the delta of Jiyuan area is compared with the normal delta.4. Sequence-paleogeographic mapping based on the sequence stratigraphic correlation and framework of Interval 8 of Yanchang Formation indicated that the delta front and predelta of expanded lake developed in chang-82 and delta plain appeared in chang-81 of Jiyuan area.