Shale gas formation conditions and potential area selection in Carboniferous strata in eastern Qaidam Basin

Drilling data and outcrops have both revealed marine source rocks in Qaidam Basin, and gas in claystone and shale of Carboniferous strata has exhibited great exploration potential. Based on an integrated study of sedimentary environment, organic matter type, abundance, and maturity, combined with outcrop data, drilling data, seismic data and non-seismic data, the authors determined residual thickness of the Carboniferous strata in eastern Qaidam Basin. The results indicate that claystone and shale are mainly concentrated in the Keluke Formation of tide flat facies in the upper part of Carboniferous strata. There are mainly two kinds of source rocks, namely carbonaceous mudstone and dark-colored mudstone with TOC of 3.08%, and the organic matter is classified as typeⅡ-Ⅲ. Evaluation shows that about 73% of the matured-high matured samples are moderate-good source rocks, and they are mainly scattered in Gaqiu, Ounan, Huobuxun and Delingha sags, forming several thickness centers. Source rocks in Shihuigou area of Ounan sag and Huobuxun sag have most promising high resource potential, and possess favorable conditions for generating shale gas.