The fluid charge and hydrocarbon accumulation,Sinian reservoir,Anpingdian-Gaoshiti Structure,Central Sichuan Basin

The Dengying Formation reservoir in the Central Sichuan Basin is old,deeply buried,and has experienced several tectonic movements in its multi-phase reservoir history. Core observation and thin section analysis show that the Dengying Formation reservoir experienced six generations of fluid charging:( 1) asphalt;( 2) dolomite;( 3) coarse grain-megacrystal dolomite;( 4)coarse grain-megacrystal dolomite;( 5) asphalt;( 6) calcite or quartz. The recorded hydrocarbon accumulation events of the fluid inclusions in the filled mineral are as follows:( 1) destruction of the early ancient oil-pools of the Sinian;( 2) reformation of the ancient oil and gas pools;( 3) the occurrence of oil-cracked to gas and the formation of the ancient gas-pools;( 4) formation of water soluble gas. Finally,the events of the formation result in the present gas accumulation. The mineral in the second to fourth generation of fluid charging was formed during the deep-burial period,which is a product of the ancient oil and gas accumulation and formation.The strontium,carbon,and oxygen isotopes of the mineral showed that the charged fluid of the Dengying Formation in the Sinian is a kind of exogenous fluid. This kind of fluid had a tendency of deep to shallow migration. The mineral from the sixth generation of fluid charging recorded the formation of the water soluble gas,which was an important event in the hydrocarbon accumulation of the Sinian reservoir. Combining the generational history and evolution of the source rocks and trap formation,this paper reconstructed the hydrocarbon accumulation process in the Sinian reservoir of the Central Sichuan Basin.