Hydrocarbon Accumulation Mechanism of Sinian Reservoir in Anpingdian-Gaoshiti Structure, Middle Sichuan Basin

The Sinian reservior in Anpingdian (安平店)-Gaoshiti (高石梯) structure, Middle Si-chuan (四川) basin, is of great importance to prospect for oil and gas. This article dissects the hydrocarbon accumulation mechanism of this area on the basis of comprehensive methods of organic geochemistry, fluid inclusion, modeling of hydrocarbon generation and expulsion from source rocks, and by combining structure evolutions and analyzing the key geologic features of hydrocarbon origin and trap. According to the fluid inclusion homogenization temperature analysis, there exist at least three stages of fluid charging in the Sinian reservoir. From Middle-Late Jurassic to Early Cretaceous, oil cracked to gas gradually owing to high temperature at 200-220 ℃. The Sinian gas pool was mainly formed at the stage when natural gas in trap was released from water and paleo-gas pools were being adjusted. It was a process in which natural gas dissipated, transferred, and redistributed, and which resulted in the present remnant gas pool in Anpindian-Gaositi tectonic belt. The authors resumed such an evolution process of Sinian reservoir as from paleo-oil pools to paleo-gas pools, and till today’s adjusted and reconstructed gas pools.