Permian’s Depositional Characteristic And Environmental Factors For High Quality Source Rocks Generation In Southwestern Area,Tarim Basin

Southwest Tarim Basin is rich in oil and gas resources, with broad prospects forexploration. However, southwest Tarim Basin has a long-term formation of depressionwith complex tectonic activities, big differences in source rock evolution and the lowquality seismic data of the study area. All these lead to the result that nowadays thebasic petroleum geological conditions of this area are lack of knowledge whichrestrict the process of exploration. So put microelements and carbon&oxygenisotopic data into this research will be a whole new start, also this new path has greatsignificance.I choose Permian as the only subject for study because the depositionalenvironment during this period is constantly changing, it’s good for geochemistry. Thepaper based on deposition theory, including those of sequence stratigraphy,sedimentary geochemistry and field work/drilling-logging data of the study area, thelithology and spatial distribution characteristic of Permian have been clarified, thencombined with the facies marks such as rock lithology and color, sedimentarystructures, paleontological to analyze its sedimentary facies and distribution, theycome out with three depositional patterns: carbonate platform pattern, mixed ofmarine clastic and carbonate pattern, continental clastic pattern. After I get the resultof microelement and carbon&oxygen isotopic test for the rock samples of Qipan,Pusige, Keziliqiman, I use two main methods which are formula method andelement ratio method to analyze the data, and then came up with the conclusion ofpaleosalinity and paleotemperature which are used for rebuilding the depositionalenvironment. We optimally select source rocks by analyzing the tests of source rocksamples and drilling data. The high quality source rock of Permian mainly developedin Qipan and Pusige formation, the average TOC is0.82%and0.80%, organic mattersare all type Ⅱwith high maturity. At last, according to the researches on depositionalcharacteristic and source rock evaluation come out a conclusion that mixed sedimentscoast and semi-deep lake are two kinds of favorable depositional environment fordeveloping high quality source rocks.