Supercritical carbon dioxide fracturing in shale and the coupled effects on the permeability of fractured shale: An experimental study

摘要

Supercritical carbon dioxide (ScCO2)-based reservoir fracturing associated with CO2-enhanced shale gas recovery is a promising technology to reduce water utilization in shale gas production and has the potential for CO2 sequestration. In the current research, experiments were conducted to explore the effectiveness of ScCO2 fracturing and the permeability of fractured shale under in situ stress and pore pressure. Computerized tomography scanning (CT scan) was used to characterize the fracture morphology. The results indicate that ScCO2 fracturing can induce complex fractures with various branches, which benefits the reservoir stimulation. There is a negative power relationship between the effective stress and permeability. However, the permeability reduction with effective stress depends on the stress path. The permeability substantially decreases with increasing effective stress, which is caused by the increase of the confining pressure. Nevertheless, the permeability decreases slowly when the increase of effective stress results from a decrease of the pore pressure. In addition, CO2 adsorption induces shale matrix swelling, influences the mechanical properties of shale, which significantly decreases the permeability of the shale, and the effect of adsorption on shale permeability is related to the stress state. (C) 2016 Elsevier B.V. All rights reserved.