Origin of Calcarenaceous Sandstone Gas Formation of the 4th Member of Xujiahe Formation in the Middle Part of Western Sichuan Depression

Key words: 
• the fourth member of Xujiahe formation (T3x4)

Abstract: Calcarenaceous sandstone is widely distributed in the fourth member of Xujiahe formation(T3x4) in West Sichuan Depression, and it can be seen in every structure and well.Most of the rocks are tight. Presently, welldeveloped pore that can be effective reservoir can be seen in local place.On the basis of thin sections identification and data statistics, the lithology, diagenesis, petrophysical properties and pore development properties for calcarenaceous sandstone in Fenggu area are analyzed in detail. It is indicated from the research that calcarenaceous sandstone layers in Fenggu are characterized by large thickness of single sand body, high content of carbonate debris, low content of calcite and welldeveloped secondary pores. Major pore type is dissolved intergrnular pores; and natural gas is mainly produced from source rock of lower Triassic Maantang formation, the third member of Xujiahe formation (T3x3) and the forth member of T3x4.Gas layers of calcarenaceous sandstone are closely related to its diagenesis,which belong to diagenetic trap.The form process of calcarenaceous sandstone gas layers in Fenggu area offers guidance for exploration of similar lithologic gas reservoirs. 