Hydrocarbon generation simulation of low-maturity shale in Shanxi Formation, Ordos Basin

Low-maturity organic-rich shale from the Paleozoic Shanxi Formation in the eastern margin of Ordos Basin was chosen for pyrolysis simulation in order to find out hydrocarbon generation laws and its influencing factors, and to reveal the hydrocarbon generation potential of shale. A pyrolysis system of sealed gold tubes in high pressure vessels was employed to conduct pyrolysis experiments at two heating rates of 20℃/h and 2℃/h under a constant confining pressure of 50 MPa. The yields of gaseous hydrocarbons and liquid hydrocarbons, and the carbon isotopic compositions of gaseous hydrocarbons were measured. The experimental products at different heating rates were analyzed, the carbon isotope characteristics and genesis were discussed, and a hydrocarbon generation model of Shanxi group was established. The research demonstrated that (1) the relatively low heating rate was favorable for the generation of hydrocarbon gas; (2) at the relatively low heating rate, both yield of liquid hydrocarbon and temperature of maximum yield were low; (3) the temperature had a significant effect on the carbon isotope of pyrolysis gas. However, the effect of heating rate on the carbon isotope of pyrolysis gas was not obvious. A shale hydrocarbon generation model was established according to the thermal simulation experiment. The results of hydrocarbon generation simulation indicated that the shale in the Shanxi Formation in the Ordos Basin had a good potential of hydrocarbon generation.