Fault development characteristics and hydrocarbon accumulation in Pingbei area of Xihu Sag, East China Sea

In the Pingbei area of the Xihu Sag in the East China Sea, faults are well-developed, and traps are mainly complex blocks. The generation stage, open/close and combination style of faults directly affect the migration, accumulation and enrichment of oil and gas. The faults in the study area can be classified into 3 types: peak-flourishing, early-flourishing and mid-flourishing. The active period of faults, the lithologic configuration at both sides of the faults and shale smear are the key elements influencing fault sealing. The faults of early-flourishing type in the Pinghu Formation boast the best sealing while those of the peak-flourishing type in the Pinghu-Huagang Formations are relatively worse. There are obvious differences in the degree of hydrocarbon accumulation between various combinations of faults. The combinations of cis-dipping faults show the highest degree of hydrocarbon accumulation; the combinations of anti-dipping faults show the lower degree of hydrocarbon accumulation; the combinations of both cis-dipping and anti-dipping faults show the middle level of hydrocarbon accumulation.