Sedimentary Microfacies of H3 of Huagang Formation in the C Oilfield of Xihu Depression in East China Sea

The C oilfield in the study area is located in the south of the central anticlinal belt of Xihu Depression, East China Sea. The H3 clastic rock reservoir of Huagang Formation in the C oilfield of Xihu Depression in East China Sea is the primary production layer. The sand body of the H3 reservoir has the characteristics of frequent lateral migration and swing, vertical stacking of multiple periods. The understanding of sedimentary microfacies and distribution patterns is relatively blind. Considering the characteristics of little offshore well data and complex geological features, by comprehensively utilizing relevant data such as cores, well logging, seismic data, and laboratory analysis in the study area, the target layer facies indicators and microfacies types were studied. The planar distribution and vertical evolution characteristics in H3 of C oilfield in Xihu Depression of East China Sea were analyzed. Research results suggested that the target area developed shallow braided river delta front subfacies, along with sedimentary microfacies such as underwater distributary channel and distributary bay. The underwater distributary channel can be further subdivided into main channel, secondary channel, and channel edge. Among them, the main channel is the favorable zone in this area, which mainly strip-like distributes, and the internal connectivity of the composite sand body is poor. So it is easy to form remaining oil rich area in the middle and late development stage. At the end of the underwater distributary channel, there are many isolated reservoirs with small sand bodies, which can form composite structure-lithology oil and gas reservoirs by overlapping with gully source fault on updip direction. Identifying the relationship between favorable sedimentary facies zones and oil-gas distribution is of great guiding significance for the deployment of adjustment wells in this and other areas.