Experimental Investigation on the Pyrolysis Characteristics of Low-Medium Maturity Shale Under Supercritical CO2

Low-medium maturity organic-rich shale reservoirs have been widely concerned due to their huge reserves and oil and gas generation potential. In this study, the pyrolysis transformation process and product distribution characteristics of low-medium maturity shale via supercritical CO2 were investigated. The pyrolysis experiments were conducted on samples from the Yanchang 7 section in Changqing oilfield at high temperature and high pressure. The variation characteristics of shale pyrolysis products under supercritical CO2 conditions compared with dry distillation conditions were studied, and then the effects of different temperatures on the composition and properties of shale pyrolysis products under supercritical CO2 were further explored. The results showcase that the yield of shale oil and pyrolysis gas under supercritical CO2 is significantly higher than that of dry distillation, and the components of oil and gas are lighter. Additionally, the change of temperature remarkably influences the pyrolysis effect of shale under supercritical CO2. The yield of shale oil and pyrolysis gas increased from 0.62% and 0.82% at 360℃ to 4.7% and 7.72% at 480 ℃, respectively, and the content of asphaltene decreased from 1.16% to 0, with the maximum reaction rate ranging from 360 ℃ to 400 ℃. The rise of temperature greatly increased the light component as well as reduced the heavy component in shale oil, while the pyrolysis gas demonstrated the law that the component becomes heavier at first and then lighter. The major discoveries of shale pyrolysis transformation process and product distribution characteristics in supercritical CO2 medium not only enrich the theoretical basis in this field, but also provide strong support for the application of CO2 capture and utilization in shale in-situ transformation.