Geochemical Characteristics of Carboniferous Hydrocarbon Source Rocks in the Eastern Qaidam Basin

Carboniferous formations are well developed on the southern Qilian Mountains in the eastern Qaidam Basin.The thick Carboniferous rocks with wide distribution are mainly dark mudstones(including carbonaceous mudstone) and carbonate rocks.To evaluate their hydrocarbon potential,30 Carboniferous mudstone-samples on outcrop sections are analysed by means of several organic geochemistry methods.Geochemical characters such as organic matter's abundance,type,maturity and biomarkers are discussed with following conclusions:The abundance of Chloroform bitumen A and hydrocarbon potential(S1+S2) is lower,while organic carbon is preferable,averaging 1.13%.The organic matters are mainly of type Ⅲ,with partly type Ⅱ2.The sedimentary organic matters are dominantly derived from higher terrigenous plants with also lower hydrobios input,and deposited in reducing environment of saline water.Except those Carboniferous rocks of Shihuiyao,Hongshanzhonggou and Baishushan area on the Zhongwulong Mountain front,which have metamorphosed,the organic matters of Shihuigou,Chengqianggou and Zhabusagaxiu area reach maturity-high maturity stage,peak period for hydrocarbon generation and expulsion.Dulan area reaches post-maturity stage.Geochemical indexes indicate the Carboniferous muddy source rocks of the eastern Qaidam Basin are preferable source rocks with large gas generation potential.