A pyrolysis study of kerogen and extracted bitumen from a lacustrine shale of the Shahejie Formation and implications for in-situ conversion processes

The in-situ conversion process (ICP) is an important industry technology to develop oil resources in medium-low maturity shales, and laboratory-based kinetics studies are an effective method to predict yields at different temperatures and heating times for the in-situ conversion process. Previous studies on ICP focused mainly on kerogen. However, these studies seldom considered the contribution of bitumen in shale, which cracks into light hydrocarbons at high temperatures and affects the yields and compositions of hydrocarbons in ICP. In this study, gold tube pyrolysis experiments of kerogen and extracted bitumen from the Shahejie Formation shale (38.72–41.21 Ma, Eocene) were conducted at two heating rates (2 and 20 °C/h) and the yields and kinetic parameters of four components (C 1 , C 2–5 , C 6–14 and C 15+ ) were obtained. Hydrocarbon yields and compositions in ICP processes are determined by applying kinetic parameters to different heating programs. For constant heating programs, the temperature determines the maximum yields in ICP. The maximum yields of methane from kerogen in ICP at constant temperatures of 300 °C, 350 °C and 400 °C are 24.08 ml/g, 99.57 ml/g and 166.82 ml/g, respectively. In addition, the percentage of methane from kerogen of the total methane yield gradually decreased to 55.22 %, 40.22 % and 31.26 %, respectively, which indicates that most of the methane is generated from extracted bitumen at high temperature. There is a maximum yield temperature for ICP, above which heavy hydrocarbons are cracked at high temperatures to produce non-hydrocarbons such as CO 2 and inert carbon, which reduces the total hydrocarbon yield. The maximum yield temperature of the Es3 x shale at 1 °C/day, 3 °C/day and 5 °C/day was 420 °C, 430 °C and 436 °C, respectively. The total hydrocarbon and gas-oil ratio (GOR) curves of ICP heating using first a rapid and then slow heating rate (the T5–1 program) and a heating rate of 1 °C/day are the highest and similar. However, when heating with the T5–1 program, it took only 0.48 years at geological conditions to reach the maximum yield temperature, saving 226 days. This study recommends the first fast and then slow heating path as the heating program for ICP. Confirming the compositions and maximum yield temperatures of ICP under different heating programs contributes to the design of engineering projects for industrial production. • Kinetics of liberating oil in-situ conversion process (ICP) from low/medium maturity shale. • Kerogen and extracted-bitumen hydrocarbons must both be considered in ICP. • Most of the hydrocarbons in ICP come from the extracted bitumen rather than the kerogen. • Fast heating then slow heating is the optimum and effective program for shale ICP.