Hydrocarbon accumulation modes of the southwest depression in Tarim Basin

The southwest depression of Tarim Basin has good prospect of oil and gas resources, and it is currently the focus of the new exploration areas. The depression structure is complicated, which has zonality from east to west, sectional division from north to south, and characteristics of deformation in different stages. Hence it can be divided into four secondary tectonic units: thrust belt in the foreland of the Kunlun Mountains, Hetian-Kashi sag zone, Mageti slope, and Yutian uplift. Four sets of hydrocarbon source rocks of Cambrian- Ordovician, Carboniferous, Permian and Jurassic and their distribution characteristics were systematically analyzed, and the oil and gas source and characteristics in the area were summarized and analyzed on the basis of an analysis of reservoir and cap rock. Seven sets of favorable reservoir- cap combinations were tentatively put forward, the faults, and unconformities and permeable formations were considered to be good conducting systems. On the basis of comprehensive analysis of above accumulation conditions, in combination with the comprehensive consideration of such factors as oil and gas source, migration way and reservoir characteristics, the authors analyzed the accumulation mode, which is divided into two major types and five sorts of modes: one type is piedmont thrust belt near the source vertical migration accumulation mode, which includes exotic thrust body, wedge shaped body and primary body, whereas the other type is slope belt distant source lateral migration accumulation mode, which includes fault-propagation folds and ancient karst. On such a basis, favorable oil and gas exploration targets are further forecasted.