Geochemical Characteristics of the Hydrocarbon Source Rock and Natural Gas of Well Taishen 1 in Qaidam Basin

Key words: 
• Qaidam basin /
• Well Taishen 1

Abstract:  Well Taishen 1 of three lake is a new exploratory well of Qaidam basin, by studying geochemical characteristics of hydrocarbon source rock of this well, the scientific basis are provided for the further exploration. Based on the information about hydrocarbon source rock, such as total organic carbon (TOC), rockeval, group composition，the characteristic of saturated hydrocarbon and biomarkers, the characteristic of aromatic hydrocarbon, the characteristic of nonhydrocarbon, the wholerock organic carbon isotope, as well as the gas isotope, this paper thoroughly analyze the geochemical characteristic of Source rocks and gas in Well Taishen 1 and its possible cause of formation. It is concluded that the 8, 14secohopanes and isofatty acids and transisofatty acids, which are relevant to the microorganism, are discovered form the chloroform bitumen "A" of hydrocarbon source rock. At the same time the existence of microorganism in the hydrocarbongenerating environment of hydrocarbon source rock are confirmed by the discrepancy between OEP1 and OEP2 and the asynchrony between C29ββ/(ββ+αα) of sterane and C31αβ22S/22(S+R) of hopance and δ13C1 of natural gas. The degree of methylation of organic matter has been reinforced by the degradation of microorganism, which are beneficial to the generating of natural gas in Well Taishen 1. It is found that the organic matter of hydrocarbon source rock in Well Taishen 1 are in the low evolution stage by OEP2 of the nalkane and pregnane and rearranged steranen and C29ααα20S/20(S+R) of sterane and the isopotal natrual gas. Some characteristic (OEP1 of the nalkane and C31αβ22S/22(S+R) of hopane) of the
hydrocarbon source rock show the mature characteristics of organic matter for the degradation of microorganism. The kerogen type of hydrocarbon source rock in Well Taishen 1  is dominated by the terrigenous higher plants, but which have the contribution of the aquatic organisms from some characteristics, such as the high abundance C20tricyclic diterpane and C20tetracycoloterpane, lupcune, perylene, retene, and the distribution of nalkane, ∑C27+C29/∑C31+ of hopance, the relative abundance of C27 and C29ααα20R in sterane, δ13C of hydrocarbon source rock and isopotal of natural gas. So the hydrocarbon source rock of Taishen 1 well are of the basis of the parent material for the generating of natural gas in the low evolution stage. The hydrocarbongenerating environment of hydrocarbon source rock in Well Taishen 1 have revealed shallow lake faciessulfsalineweak reducingweak oxidizing environment reducing environment by the elemental eight sulfur ring and the biomarker characteristics.