Abstract:

For the purpose of figuring out the characteristics and genesis of shale gas from the Carboniferous marinecontinental transitional facies strata in the eastern Qaidam Basin, the research was carried out by extracting the shale and shale gas from the Carboniferous Keluke group of the Well Chaiye 2, through the rockeval pyrolysis experiments and microscopic examination for the shale samples, shale gas field desorption, gas composition testing and carbon isotope analysis indoor. The research results indicate that Carboniferous marinecontinental transitional facies coal measure strata developed 4 types of organic rich sediments of dark shale, carbonaceous shale, coal and marl in the Qaidam Basin. The mean values of TOC are 3.46%, 12.34%, 77.62% and 1.89%, respectively. The kerogen is mainly of type Ⅲ and type Ⅱ2, which is at highly mature stage with the organic material to generate considerable amount of shale gas. The level of nitrogen is higher than others in the Well Chaiye 2 according to the shale field analysis of shale gas which also contains considerably small amount of Ar and He. Methane contributes the largest part of hydrocarbon gases and they are generally dry gas. The distribution percentage of methane stable carbon isotope ranges from -48.6% to -39.8%, which is between marine and continental shale gas, having a bias towards carbon. Shale gas contains thermogenic gas as its largest amount of composition and biogenic gas as the second.

Key words: shale gas, genesis, marine continental transitional facies, Carboniferous, Qaidam Basin