Pyrolysis Mechanism and Reservoir Simulation Study of Organic-Rich Shale during the In Situ Conversion via Supercritical Water Heating

The low-medium maturity shale reservoir has garnered substantial interest because of its huge reserves and promising hydrocarbon generation potential. In this paper, a self-designed high-temperature and pressure pyrolysis experiment device was constructed. Experiments involving thermogravimetric pyrolysis and isothermal pyrolysis in supercritical water (SCW) environments were carried out on samples from the Longkou shale. The effect of SCW on organic-rich shale pyrolysis was understood by comparing the product characteristics of shale pyrolysis in SCW environments with dry environments. The complete kinetic models of kerogen pyrolysis in dry and SCW environments were established by fitting the composition characteristics of pyrolysis products using the nonlinear least-squares method. The numerical simulation of shale in situ conversion via SCW injection and electrical heating was investigated, and the performance evolution of thermal-reactive flow coupling was clarified. The results showed that SCW reduced the main temperature window of kerogen pyrolysis, and the total mass loss increased by 46.29% compared to that in a dry environment. SCW promoted the generation and subsequent release of pyrolysis hydrocarbons. SCW altered the compositional profile of the generated products, mainly by increasing CO2 content in pyrolysis gas, reducing olefin content, and effectively improving oil quality compared with the dry environment. SCW reduced the activation energy of kerogen pyrolysis by 41.65%, indicating that the reaction is more easily activated. More hydrocarbon products and less coke were generated. The superiority of kinetic models holds significant practical implications for the application of SCW heating organic-rich shale in situ conversion technology. The shale in situ conversion via SCW greatly shortened the production cycle and improved cumulative oil. Kerogen within the interwell region was completely pyrolyzed, the reservoir porosity increased to 2 times of the original value, and permeability was enhanced by 10 times after shale in situ conversion via SCW for 3 years.