Multiple phases of hydrocarbon generation and migration in the Tazhong petroleum system of the Tarim Basin, Peopleʹs Republic of China

Organic petrology, organic geochemical analysis and fluid inclusion methods were employed to investigate a series of core samples from the Tazhong Uplift. Bitumens and organic inclusions were found to occur widely in Paleozoic rocks, especially carbonates, and both can be subdivided into three groups. The reflectance ranges of the three bitumen groups are: 1.30-1.60% (I); 0.50-0.80% (II); and 0.15-0.40% (III), respectively, and the corresponding organic inclusion groups are: dark yellow fluorescence organic inclusions with a homogenization temperature of 200–240°C; blue-green fluorescence organic inclusions with a temperature of 160–200°C; and the strong yellow fluorescent organic inclusions with a temperature of 80–130°C. The wide occurrence of the three group bitumens and organic inclusions in the Tazhong Uplift reveals that there were three periods of large-scale oil migration and accumulation in this area. The analysis of hydrocarbon-generating history based on paleotemperature and burial history of source rocks shows that they underwent three oil-generating peaks, in Early Ordovician, Triassic and Cenozoic, respectively, which led to three phases of hydrocarbon generation and migration. It is believed that the Tazhong Uplift is an old uplift rich in oil and gas, and has been fed with oil and gas from nearby source areas during a long geological history, and also that it has great hydrocarbon potential.