The percentage of gas production from low-permeability gas reservoirs is increasing in China.However

the low-permeability gas reservoirs are geologically complex and can not be predicted easily

impeding their exploration and development.The second member of the Upper Triassic Xujiahe Formation in western Sichuan depression of Sichuan basin has poor poroperm characteristics as a whole and belongs to low porosity and permea-bility reservoirs.Based on the study of reservoir characteristics and diagenesis

this paper determines the filling sequence and relative content of cements of each stage through microscopic observation of thin sections.Characteri-stic inclusions are identified in cements of each stage and used to measure temperature.The results in combination with burial history and thermal history are used to determine the forming time of cements of each stage

hydrocarbon charging time and their sequences.In addition

the paper describes the rate and causes of porosity change in different periods

reconstructs the reservoir forming history and determines the time of reservoir tightening.Finally

this paper presents further exploration targets according to the analysis of hydrocarbon charging history.