Numerical study on filtration law of supercritical carbon dioxide fracturing in shale gas reservoirs

Abstract

AbstractSupercritical carbon dioxide (SC‐CO2) fracturing can form more complex fracture network and avoid reservoir damage, making it a lucrative alternative to hydraulic fracturing in shale gas reservoirs. This study establishes a two‐dimensional dynamic filtration model of SC‐CO2 fracturing, which considers stress sensitivity, fluid adsorption, dynamic changes of fluid physical parameters, and coupled fracture propagation. According to the established model, the dynamic filtration of fracture elements and matrix pressure variation in fracture propagation are simulated and analyzed. And the influence of dynamic and static filtration model, constant and variable SC‐CO2 physical parameters, and fluid types in the filtration areas on the calculation results, as well as the effects of stress sensitivity and fluid adsorption on the filtration process are analyzed. The results show that during the fracturing process, fracture elements’ average filtration rate gradually drops and finally becomes stable, while the cumulative filtration volume increases nearly linearly. The static filtration model of uncoupled fracture propagation or the simplification of fluid in the filtration areas to SC‐CO2 single phase provides the reduction of calculation results, while constant SC‐CO2 physical parameters or the fluid simplification to the methane (CH4) single phase have the opposite effect. Stress sensitivity can accelerate the filtration, while fluid adsorption can slow down the filtration. The influence of stress sensitivity is maximal at the middle stage of fracturing, while the influence of fluid adsorption weakens with time. This study's findings have important guiding significance for the optimal design and field application of SC‐CO2 fracturing in shale gas reservoirs. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.