Maturity evolution of the Carboniferous source rocks(CSR) in the Tarim Basin, Northwest China
Chang Jian1,2, Qiu Nansheng1,2, Liu Yifeng1,2, Li Huili3, Que Yongquan1,2
1. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249;
2. Research Center for Basin and Reservoir, College of Geosciences, China University of Petroleum, Beijing 102249;
3. SINOPEC Petroleum Exploration and Production Research Institute, Beijing 100083
For the Carboniferous of the Tarim Basin,although it is rich in source rocks and the crude oil which generated were found,the studies on its thermal evolution are very few. Based on the geological data,paleo-geothermal gradient and measured vitrinite reflectance data,we simulated the thermal evolution of the Carboniferous source rocks(CSR)of 6 typical wells in the Tarim Basin and rebuilt quantitatively the maturity distribution characteristic of the base and top of the CSR in the end of Permian,the end of Triassic,the end of Cretaceous and present-day,respectively. As the deposition centers,the massive sediments were deposited in the southern Tabei uplift,Southwest depression and Awati depression during the Carboniferous and the Permian,which caused the maturity evolution of the CSR in these areas. In the end of Permian,the maturity of the base of the CSR in the southern Tabei uplift,Southwest depression and Awati depression reached to 0.9%～1.3%(middle-high maturity) and the top was just 0.5%～0.9%(low-middle maturity),which indicated that these areas were favorable to generate oil in the Permian. The CSR in the central-eastern Tarim Basin always stayed in the maturity evolution stage due to the long-term deposition in the Mesozoic. The maturity of the base of the CSR in the Tazhong low-uplift and Manjiaer depression was 0.7%～0.9%(middle maturity) and their top was 0.5%～0.7%(low maturity) in the end of Cretaceous,while the base of the Tangguzibasi depression was 0.9%～1.1%(middle-high maturity)and its top was 0.7%～0.9%(middle maturity). The Southwest depression and Bachu uplift experienced uplift and erosion during the Mesozoic and the maturity of their SCR stopped evolution due to the distant effect from the collision among the Qiangtang block,Lhasa block and Indian plate with the southern margin of the Eurasia continent. Since the Cenozoic,the Southwest depression and Awati depression developed as the foreland basins and received massive sediments again,which caused the rapid evolution of the maturity of the SCR. The maturity of the base and top of the SCR in the Southwest depression and Awati depression is larger than 2.0% now and stays in the dry-gas stage. The maturity of the SCR in the Manjiaer depression always stayed in evolving since the Carboniferous and reach to the maximum with 0.8%～1.0% now. In addition,the potential area of secondary hydrocarbon generation for the SCR were the Southwest depression and Awati depression. This study not only enriches the research on the thermal histories of the SCR,but also provides guidance for the oil and gas exploration and exploitation in the Tarim Basin.