Quantitative evaluation of reservoir-cap rocks in the biogas reservoir of eastern Qaidam Basin

The reservoir-cap rocks of the Quaternary biogas reservoirs in eastern Qaidam Basin are still in their early diagenetic process. Quantitative evaluation has been conducted by comprehensively considering lithology, physical properties and gas-bearing property. The evaluation parameters include displacement pressure, shale content, porosity and gas saturation. Logging calculation models are set up respectively for each parameter. Multi-parameter comprehensive evaluation method and criterion are presented for the effectiveness of reservoir-cap rocks. This method has been applied to 5 gas fields in the study area including Sebei I, Sebei II, Tainan, Taijnar, and Salt Lake. The evaluation result is consistent with biogas distribution, indicating the effectiveness of this method.