Pore evolution characteristics of organic matter pore for Jurassic shale in the middle part of northern margin of Qaidam Basin

The Jurassic shale in northern margin of Qaidam Basin is characterized by high organic carbon content, large thickness and wide distribution.However, due to immaturity-low maturity of organic matter, the formation and characterization of shale gas in this area are restricted.Through heating experiments under an open system, the development characteristics and evolution process of shale organic matter pores at different temperatures were systematically characterized. Analysis shows that the thermal simulation temperature of 200~400℃ is the dominant temperature range for the development of organic matter pores, with a large number of pores, ranging from micropores to macropores, which can form a network connection between the pores.After that, with the further increasing of temperature, the pore will appear "collapse" phenomenon, which will inhibit the occurrence of shale gas.Besides, the pore development of organic matter is also heterogeneous, and the pore development of different organic matter macerals is different.The pore development in vitrinite and exinite is relatively slow, and the transformation of organic matter is not complete.However, the pore development of organic matter macerals, mainly composed of bituminite, alginite and amorphous body, are early and strong, and connectivity between pore is good, which are the major contributors to shale gas reservoir space.In addition, combined with EDS analysis, it is considered that the development of organic matter pore is mainly controlled by the weight percentage of elements and the content of alkaline earth elements such as Ca, Mg.