Characteristics of Triassic marine source rocks and prediction of favorable source kitchens in Qiangtang Basin, Tibet

Qiangtang Basin is an important exploration target in Tibetan area that was conducted little exploration and research before this study. Xiaochaka Formation is major source rocks in Upper Triassic, Mesozoic in the basin. According to the evaluation standard of source rocks established specially in this basin, the occurrence features of this formation in different structural units was analyzed comprehensively and then the favorable source kitchens were predicted on the aspects of its sedimentary environment, thickness and organic geochemical characteristics. The work was conducted on the samples from many geological profiles in field survey routes and the analytical data on organic carbon, maceral, rock pyrolysis, vitrinite and bitumen reflectance, and carbon isotopes, etc. The conclusions are as follows: firstly, the organic matter abundance of limestone and mudstone in Xiaochaka Formation is high so that they belong to medium-good source rocks; however, the actual areal division of their distribution shows by the fact that the values are variable in different areas; this formation mainly distributes in the middle part of Southern Qiangtang Basin with mainly II(B) organic matter type and high maturity; limestone is slightly better than mudstone in organic matter type, but smaller in the favorable source kitchens. All the above-mentioned research has an important reference meaning for the further determination of major source rocks, resource evaluation and exploration prospect on oil and gas.