GEOCHEMICAL CHARACTERISTICS AND EVOLUTION OF HYDROCARBON-GENERATION OF THE LUCAOGOU FORMATION SHALES, JIMUSAER SAG, JUNGGAR BASIN

Lacustrine shale oil in the Middle Permian Lucaogou Formation, Jimusaer Sag, eastern Junggar Basin is currently one of the hotspot of shale oil exploration in China. In present study, geochemical characteristics of 137 source rock samples from 14 wells were analyzed by a series of experiments (pyrolysis, total organic carbon (TOC), content of soluble organic matter, biomarker, whole-rock organic microscopic component, and vitrinite reflectivity) of The sedimentary environment, hydrocarbon-generation capability of the Lucaogou Formation shales in the Jimusaer Sag were also discussed. Based on the above-mentioned parameters combined with basin modeling and a hydrocarbon-generation pyrolysis simulation experiment under a closed system, the evolutions of hydrocarbon generation in the Lucaogou Formation shales were established. The maximum quantity of hydrocarbon yields and expulsion efficiency of the shale hydrocarbons were also estimated. The results indicated that the organic matter inputs of the Lucaogou Formation source rocks were dominated by algae and samples were deposited in high-salinity and reducing environment. Samples in present study are a set of oil-prone source rocks. The rock samples are featured by a high hydrocarbon generating capability and heterogeneity. At the end of the Cretaceous period, the Lucaogou Formation shales entered into the oil-generating window. Currently, the shales in the deep part of the sag were in high-maturity stage and generated massive amounts of high-maturity oil and condensed gas. For shales from shallow areas featured by low maturity, only massive amounts of conventional crude oil were generated. Pyrolysis simulation results showed that the Lucaogou Formation shales have a maximum oil generation of 220.2 mg/g TOC and an estimated maximum hydrocarbon expulsion efficiency of 59.3%similar to 76.4%.