Abstract: Tazhong 40 oilfield is a small field recently proved in Tarim basin. Its reservoir is Donghe sandstone of Carboniferous. A lot of fluid inclusion enclaves were formed during its hydrocarbon accumulation with uniform temperature of the enclaves being divided into two intervals ranging from 88.6~100.73 C to 122.1~144.7 C. They reflect different time and depths or represent two different stages of hydrocarbon accumulations. According to the reservoir buried history, thermal alternation history and hydrocarbon source rock evolution history, it is supposed that Jurassic is the first stage of hydrocarbon accumulation, but almost all of its oil pools had been destroyed due to tectonic movements occurred afterwards; Tertiary is the second stage of it and no destruction takes place. It is found from fluorescent thin section that existence of oil-asphalt among quartz secondary outgrowth rims and quartz grains could be formed during the first stage. The results of reservoir diagenesis research show that the time and depth for secondary hydrocarbon accumulation are consistent with the conclusion from fluid inclusion enclave. This explains that using the uniform temperature of fluid inclusion enclave to study stages of hydrocarbon accumulation into reservoirs is feasible, and the conclusion is right.

Key words: Tarim basin, Tazhong 40 oilfield, fluid, inclusion enclave, reservoir formation, temperature