Organic Geochemical Characteristics of the Mud or Shale in the Lower Permian Shoushangou Formation of West Ujimqin Banner, Inner Mongolia:A Case Study of Well MXD1

To evaluate such problems as the hydrocarbon potential of the thick mud shale and the hydrocarbon generation potential of depositional environment, the origin of parent materials and the maturity, the authors carried out for the first time systematic organic geochemical research on the dark mud shale in Shoushangou Formation of Well MXD1 in West Ujimqin Banner, Inner Mongolia.The n-alkane peak form and the main peak in the second member indicate that the organic matter on the whole has not been affected by biodegradation.The relative content of regular steranes, the Carbon Preference Index and tricyclic terpanes/17α-hophane features show that this member was deposited in saline water facies of the reducing environment, and its source was mainly aquatic and partly terrigenous; and it is also proved that the sedimentary environment was mainly of marine facies.The peak shape of positive alkanes, the relationship between Pr/nC₁₇ value and Ph/nC₁₈ value and the relative content of the normal sterane suggest that the parental materials of organic matter is mainly of Type II.The characteristics of aromatic organic chromatin can reflect the maturity of the source rock, which is highly mature-over-mature.The characteristics of aromatic organic chromatin materials such as Trimethylnaphthalene, Phenanthrene, triaromatic steroid and the characteristics of saturated hydrocarbon chromatography such as hopane series, sterane and Methylphenanthrene all show that its hydrocarbon source rock has high maturity, and the average of vitrinite reflectance is 2.93%, which implies that the maturity of organic matter is mature-over mature, beneficial to the formation of natural gas.The residual organic carbon content of the samples is 0.10% to 0.85%, and the original total organic carbon content recovered is 0.17%~1.46%, with an average of 0.51%, so part of the shales or mudstones in Well MXD1 can reach the level of medium hydrocarbon source rocks.The comprehensive evaluation suggests that the hydrocarbon source rock of Well MXD1 is of medium hydrocarbon potential.The research results show that the upper Paleozoic strata in the study area have hydrocarbon source conditions for oil and gas reservoirs, and provide an important basis of organic geochemistry for oil and gas exploration in the Paleozoic strata of West Ujimqin Banner.The results obtained by the authors have certain reference significance for the new-area gas exploration in Carboniferous–Permian strata of Erlian Basin, and also provide useful materials for the oil-gas exploration strategic succession and sustainable development of North China.