Geochemical Characteristics Of Carboniferous Source Rocks In Wuwei Basin

Wuwei basin is located in the eastern part of the Hexi corridor Qilian-Alashan area.Carboniferous strata is one of the areas which are better development and conservation,it has good petroleum geological conditions.Carboniferous strata is a set of transitional facies,it is the main hydrocarbon source rock in Wuwei basin.The Carboniferous strata developed completely,and these groups are shown to Qianheishan formation,Chouniugou formation,Jingyuan formation,Yanghugou formation and Taiyuan formation from bottom to top.Hydrocarbon source rocks are mainly mudstone,shale and limestone.This paper is writing by the research of the outcrop section and probe section in the field of Wuwei basin.The method analyzing organic geochemistry testing technology and establishing a comprehensive outcrop section geochemical field.In addition,this paper is analysis the carboniferous hydrocarbon source rocks organic matter abundance,type,maturity,and biomarker compound characteristic comprehensively of the Wuwei basin,and discusses the basin hydrocarbon source rocks organic matter.Its sedimentary environment based on previous studies.The Carboniferous hydrocarbon source rocks organic matter abundance of Wuwei basin is generally high.The distribution of carbon isotope composition is between-20.1‰ and-26.5‰.the main type of organic matter is ? kerogen,and the minority type is ?2 kerogen.The peak temperature of pyrolysis Tmax value in different layers of hydrocarbon source rock samples is generally more than 435?,and it has high maturity stage of thermal evolution.The main type of Carboniferous hydrocarbon source rocks n-alkanes is after high low before bimodal type and the n-alkanes ?nC21-/?nC22+ is mainly distributed between 0.8 to 2.0,it is dominated by the lightweight component of saturated hydrocarbon.From the lower Carboniferous to upper Carboniferous series,the biological sources transition from the lower phytoplankton to the higher plants.The main distribution of source rock Pr/Ph is about 0.5 in Wuwei basin,the Pr/nC17 is mainly distributed between 0.53 to 1.0,and the Ph/nC18 is mainly distributed between 1.0 to 1.6.This result shows that the dominance of phytane,and the environment is weak restore to restore environment transition.The ???20RC27 sterane is absolute advantage of the lower Carboniferous source rock samples,it shows "L" type.The pregnant sterane compounds content is basic on the high level,the upper Carboniferous shows "V" type,and the pregnant sterane compounds content are decreased.C19-C23 tricyclic terpane is basic on the rising-falling-rising trend,and the relative content of Ts is close to Tm.Gamma paraffin wax content is higher.Carboniferous hydrocarbon source rocks has high content of pyrene,flexor compounds,but naphthalene,anthracene,polycyclic aromatic compounds has low content.Fluorene series compounds is in the transitional environment,Carboniferous sedimentary basin is transiting by reductive environment to the weak oxidizing environment,and the composition of biological source is transiting by lower aquatic to terrigenous higher plants.