Hydrocarbon Accumulation Study In Paleozoic Clastic Formations, Central Tarim Basin

Tarim Basin, the largest marine superimposed basin in China, major breakthrough has been obtained in the lower Paleozoic carbonate formations, however, researches in clastic formations of Paleozoic have not yet systematically begun. Making clear about the main controlling factors of the clastic reservoir and making reasonable prediction of hydrocarbon accumulation in clastic rocks can be beneficial for clastic formation exploration and which can also inject new vitality to West-East Gas Transmission project of China.The hydrocarbon accumulations in Siluran and Devonian are characteried by multiple sources by virtue of oil-source correlation. According to the study, the early source rock was Cambrian-lower Ordovician which mainly provided oil in the early evolution stage and the middle-upper Ordovician was the late source rock with gas generation from the early source rock.With the help of fuild inclusion observation under microscope, homogeneous temperature testing, salinity testing and biomaker characteristics, the hydrocarbon accumulation period was determined. Accordting to the result, Silurian formation was charged by hydrocarbon for three times and two times for Devonian formation.The hydrocarbon migration routes of Silurian and Devonian formations were determined by virtue of nitrogen compounds and trace elements of fluid inclusions. The result indicates that two migration directions for hydrocarbon charge in Silurian. One is from northwest to southeast and the other is from northeast to southwest. The evidence for vertical migration in Silurian is also obvious. For Devonian formation, in the west of Tazhong area, the charge direction is from northwest to southeast, however, there are two charge directions in the east of Tazhong area for Devonian formation and one is from northwest to southeast and the other is from northeast to southwest.By integrating multiple factors, the controlling factors of hydrocarbon accumulation were fixed. The couduit system including faults and favorable sand, volcanic rocks, paleo-uplift with continuous development and hydrocarbon generation center are the main controlling factors for hydrocarbon accumulation and distribution. Adopting multi-factor superimposed method to divide the favorable hydrocarbon accumulation areas for both Silurian and Devonian formaiton. According to the study, the favorable areas for Silurian formation distribute in the west-central parts of the central fault horst zone, while the favorable areas for Devonian formation distribute along the TazhogⅡf ault belt and the west end dump of Tazhong 10 fault belt.