Abstract: The biogas in Qaidam basin is primarily produced in Qigequan formation of Quaternary in east-central Qaidam basin and lacustrine sediment of Palaeogene Shizigou formation. Based on sedimentary environments and geologic features of the two formations, by means of great amounts of data and studied results from paleontology, bacteria investigation, biochemical gas production modeling experiment, logging and lab analysis, this paper describes the biogas accumulating conditions in this basin, including space environment adapted for bacterial growth and multiplying, enough and durative gas supply, the best source-reservoir-caprock assemblage. It is suggested that timely trapping and good preservation conditions are the necessary prerequisites for biogas accumulations in Qaidam basin.

Key words: Qaidam basin, biogas, gas reservoir, condition