Main controlling factors of hydrocarbon accumulation and favorable exploration zone in West Shanan Sag

After the exploration for many years, geologists have failed to find commercial oil and gas in West Shanan Sag, where its exploration potential has long been questioned. Based on the comprehensive study of structure and tectonic evolution characteristics of West Shanan Sag, the founded oil and gas reservoirs and hydrocarbon accumulation characteristics were analyzed systematically. The result shows that the structure style of West Shanan Sag controls the direction of oil-gas migration;the effectiveness of trap controls the fullness degree; the development of Paleogene reservoir controls the size of hydrocarbon accumulation; the movement stage of fault controls the distributed layers of oil and gas. The main reason of failure in West Shanan Sag drilling is that Shazhong structural belt, with the highest exploration degree, isn ′ t located in the path of predominating migration directions; poor effectiveness of trap and poor reservoir development in Shahejie Formation are important reasons for the small size of hydrocarbon discoveries. Finally, it is pointed out that the slope belts on both sides of West Shanan Sag are considered as relatively favorable exploration zones, in which the south slope belt has a great prospective.