Evaluation of organic matter abundance of source rocks of biogenic gas: a case from the Quaternary Qigequan Formation Shale, Sanhu Depression, Qaidam Basin

A correct understanding of organic matter abundance is key to understanding the conditions necessary for generating biogenic gas, seeking favorable exploration intervals and fields and evaluating resources correctly.The Qigequan Formation shale of the Quaternary in the Sanhu Depression of the Qaidam Basin is taken as the research object.The abundance of dissolved organic matter was determined through total carbon, pyrolysis and other experiments.The evaluation criteria were established and applied.The resource quality is calculated.The results are as follows.(1) Dissolved organic matter is the basis for biogenic gas generation and should be emphasized in the evaluation.(2) The shale has a relatively high dissolved organic carbon (DOC) content, with an average of 2.48 times that of insoluble organic carbon.(3) The DOC of the good source rock is more than 0.60%, that of the medium is 0.25~0.60%,and that of the poor is less than 0.25%.(4) The distribution of good source rocks is influenced by the position and depth of the water column and the paleoclimate.Favorable intervals are mainly in the upper sections of K10, K9 and K8 and the middle section of K7.The favorable areas are mainly the Tainan, Sebei and Sedong areas.