Evaluation of Carboniferous source rocks in Qaidam area

Organic geochemistry measurements and analyses were conducted on Carboniferous dark-colored mudstones,carbonates,coals and carbonaceous mudstones in marginal areas around the Qaidam Basin.The results indicated that the Carboniferous source rock consists predominantly of dark-colored mudstones among which coals and carbonaceous mudstones probably have hydrocarbon-generative potential.The lower Carboniferous dark-colored mudstone generally has poor to moderate contents of organic carbon,while the upper Carboniferous one contains a good or very good abundance of organic carbon.However,the upper and lower Carboniferous dark-colored limestone shows a lower content of organic carbon,constituting only a non-to poor-source rock.Mudstones with good source potential developed mainly in deposits of tidal flat,lagoon and marsh facies and horizons occurring in the middle Huaitoutala Formation,Keluke Formation and the lower Zhabusagaxiu Formation were evaluated as a good or very good source rock.Organic matter in the samples is mainly dominated by type II and III kerogens,and all the source rocks,except for the Dulan and Geermu areas where they have been at the post-mature stage to generate dry gases,are in a peak period of oil generation and expulsion with a moderate maturity of organic matter,thus,they have a good petroleum prospect.