Carboniferous-Permian’s Depositional Characteristic And Source Rock Evaluation In Southwestern Area, Tarim Basin

Southwest Tarim Basin is rich in oil and gas resources, with broad prospects for exploration. April 4, 2010, the discovery of the high-capacity oil and gas flows in well Kedong-1 had been the first major breakthrough in foreland of Kunlun mountains since 33 years ago, meanwhile, laboratory analysis data showed the source rock came from Carboniferous– Permian which proved us the bright possibilities in finding oil and gas in the structural belt of Kedong maybe the entire southwest Tarim Basin. However, southwest Tarim Basin has a long-term formation of depression with complex tectonic activities, big differences in source rock evolution and the low quality seismic data of the study area. All these lead to the result that nowadays the basic petroleum geological conditions of this area are lack of knowledge which restrict the process of exploration. As the region’s major source rocks, doing researches on Carboniferous– Permian’s depositional characteristic and source rock evaluation has great significance.My paper based on deposition theory, including those of sequence stratigraphy, seismic stratigraphy and field work/drilling-logging/ seismic data of the study area, the lithology and spatial distribution characteristic of Carboniferous-Permian have been clarified, then combined with the facies marks such as rock lithology and color, sedimentary structures, paleontological to analyze its sedimentary facies and distribution, they come out with two depositional models: carbonate platform and clastic shore-mixed sediments coast, divide the Carboniferous-Permian sedimentary evolution into three stages and seven sequence. We optimally select source rocks by analyzing the tests of source rock samples and drilling data. The high quality source rock of Carboniferous mainly developed in Heshilafu formation and Kalawuyi formation, with wide distribution, large thickness and higher organic matter abundance, the average TOC are 1.06% and 0.98%, organic matter is typeⅡwith high maturity. The high quality source rock of Permian mainly developed in Pusige formation, with the similar advantages of Carboniferous, the average TOC is 0.80%, organic matter is typeⅡwith high maturity. At last, according to the researches on depositional characteristic and source rock evaluation come out a conclusion that mixed sediments coast and semi-deep lake are two kinds of favorable depositional environment for developing high quality source rocks.