Abstract:

Mesozoic marine black shales are mainly distributed in the Qiangtang Basin, QinghaiTibet plateau, in the Upper Triassic Xiaochaka Formation（T3x）， the Jurassic Buqu Formation (J2b) and the Suowa Formation (J3x).  They are formed in the reducing sedimentary environment which is abundant in organics that are easily preserved. The sedimentary facies are mainly platform facies, followed by basinal facies and delta facies. The thickness is 41474 m; TOC is 0.25%8.34％; organic matter is typeⅡ; the average value of Ro is 1.21%3.0％, showing in the gas stage of highover mature. The brittle minerals are mainly quartz and feldspar, total contents are 65%70%, and the shale porosity is about 2%. Compared with each index of gas shales in the main basins of American, we can consider that the Mesozoic marine black shales in Qiangtang Basin have the features of large deposition thickness, low organic abundance, high maturity of thermal evolution, numerous species of brittle minerals, low content of quartz, high content of feldspar and clay minerals, and low porosity. It means that the shales have the condition of producing shale gas and the basin is one of the sedimentary basins, in which the marine shale gas could be explored. From the comprehensive evaluation of the shale gas prospective areas, it can be predicted that in the Upper Triassic Xiaochaka Formation shale gas is widely distributed, followed by the Buqu Formation and the Suowa Formation.

Key words:  Qiangtang Basin, Mesozoic, marine shale, shale gas, formation conditions, prospective area