Distribution characteristics and evolution of the central axial stream channel under the stratigraphic framework of the Huagang Formation in the Xihu Sag, East China Sea Shelf Basin

The Xihu Sag is the largest subunit of the East China Sea shelf Basin. The discovery of several large gas fields in the Xihu Sag shows excellent oil and gas storage potential. This paper focuses on the braided river in the Huagang Formation (HF) central axial channel in Xihu Sag. The seismic data, drilling data to establish sand prediction models under the HF’s high-resolution sequence stratigraphic framework. Further combining seismic attributes, constrained sparse pulse inversion, and post-stack geostatistical inversion methods under the model to research the braided river’s characterization finely. From the perspectives of paleo-geomorphic terrace morphology, sand development stage, external structure, and internal depositional composition, the sizeable axial sand of the HF in the north-central study area of the Xihu Sag are researched and established the sands evolution model in the north-central Xihu Sag. There are large-scale canyon erosion landforms with multiple terraces spreading in the northeast. The channel width is small in the braided channel’s upper reaches, the sand has a limited cross-spread range and evident down-cutting erosion, and the sand is thicker, with the characteristics of “narrow and wide.” The braided channel center is dominated by thick sand with good lateral continuity. The delta front was the main sedimentary facies in the study area, and the underwater distributary channel was the most critical sedimentary microfacies, which provides reliable data for finding favorable reservoir areas in Xihu Sag to provide evidence support for oil and gas exploration in the East China Sea.