Differential evolution and the influencing factors of low-maturity terrestrial shale with different types of kerogen: A case study of a Jurassic shale from the northern margin of Qaidam Basin，China

The Jurassic terrestrial shale on the northern margin of Qaidam Basin is characterized by high contents of organic matter but low maturity resulting in a lack of further research on shale gas in this area. To better understanding the shale gas potential of organic matter with different types, we conducted thermal maturity experiment of hydrocarbon generation from different kerogen types of low-mature shales under closed conditions. The results show that type II and type III kerogen have experienced similar hydrocarbon generation stages, but they differ in the hydrocarbon generation interval and evolution process between liquid hydrocarbon and gaseous hydrocarbon. Compared with Type III kerogen, type II kerogen is characterized by a low initial temperature at each evolutionary stage and wide temperature range, which caused the overall evolution of type III Kerogen lagged behind that of type II kerogen. The differential evolutions mainly result from the differences in hydrocarbon generation mechanism, hydrocarbon generation activation energy and kerogen macerals among different kerogen types. We summarized the evolution model of type II and type III Kerogen based on the characteristics of kerogen in hydrocarbon generation, carbon isotope change, pore development and other aspects. This work can provide theoretical and data support for reconstructing the hydrocarbon generation process of terrestrial shale gas, investigating the hydrocarbon generation mechanism, and predicting the hydrocarbon resources of terrestrial shale oil and gas on the northern margin of Qaidam basin and even China.