On time-space matching of hydrocarbon accumulation in the Yuquan Structure, Xihu Sag

Based on well logging and geochemical data including fluid inclusions and authigenic illite isotopes, geological evolution in faults, trapping, burial, diagenesis, hydrocarbon generation, oil and gas accumulation, and their spatio-temporal matching in the Yuquan Structure, Xihu Sag was studied using balanced profiling and basin modeling technology. Result shows that the Yuquan Structure experienced three stages in geological evolution: pre-compression inversion stage, early compression inversion stage, and late compression inversion stage, of which the early and late compression inversion stages are the key stages for the development and finalization of NWW regulating faults and traps. The lower member (H6-H7) of the Huagang Formation has been continuously filled with oil and gas since 13.0 Ma, and the reservoir physical properties are poor. The upper member of the Huagang Formation has been filled with oil and gas in 13.0 Ma to 11.4 Ma, and 4.2 Ma to the present. The second stage is the main oil and gas accumulation period, and the reservoir physical properties are good. The Longjing Formation has been filled with oil and gas from 3.4Ma to the current stage, and the reservoir physical properties are the best. The key points of finding favorable exploration targets for the Yuquan Structure include that the upper part of the Huagang Formation shall be taken as the main exploration target layer near the early-developed NNE oil-source fault, and the late NWW regulating fault shall be avoided. It is pointed out that the upper part of the Huagang Formation in the northern part of YQ-3 well block and the northern part of YQ-1 well block, the Longjing Formation in the hanging wall of NWW fault in YQ-3 well block, and the upper part of the Longjing Formation in YQ-1 well block are favorable exploration areas.