Seismic sedimentological analysis of coal stratigraphy of Pinghu Formation in the Pinghu slope belt, Xihu Sag, East China Sea Shelf Basin

The Pinghu Slope belt in the Xihu Sag is rich in oil and gas resources. Pinghu Formation, the main target layer, is a set of coal bearing strata bearing marine-continental transitional facies in large burial depth and complex sedimentary environment. However, the reservoir distribution in it remains unclear. Based on the data of seismic, core, and logging, we deeply analyzed the response characteristics of coal measures of the Pinghu Formation in the slope belt, established the isochronous stratigraphic framework of high-precision coal seams, and recognized lowstand systems tract, transgressive systems tract, and highstand systems tract in the third-order sequence. Under the constraints of sequence framework, technologies such as multi-data iterative analysis, multi-attribute comprehensive analysis, and seismic facies identification and splicing were applied innovatively to the research in seismic sedimentology, to transform from seismic facies to sedimentary facies effectively, and to reconstruct regional sedimentary system. Results show that the SQ3 lowstand system tract reflects constructive deltas in early stage and meandering rivers in later stage, during which channels developed along the long axis of Xihu Sag. The transgressive systems tract manifests small-medium–sized tidal channels perpendicular to shorelines. The highstand systems tract indicates deltaic plain deposits, of which large-scale NW-SE distributary channel deposits are dominated.