Enhancing porosity and permeability of shale matrix through supercritical water treatment

Hydraulic fracturing is widely used in the exploitation of shale gas reservoirs to create high conductivity fractures and complex fracture networks. However, the low flowback efficiency of the fracturing fluid means that a large amount of fracturing fluid is retained in the shale formation, which can cause formation damage. Based on the condition of shale gas reservoirs and the characteristics of supercritical water, a supercritical water treatment (SCWT) method is proposed for alleviating formation damage and enhancing the gas transportation capacity. A simulation experiment is conducted and the changes of various parameters and properties of shale samples after SCWT are measured and analyzed. The experiment results show the permeability of LMX-1 and LMX-2 increased by 191.02 times and 197.06 times, respectively, the porosity of LMX-1 and LMX-2 increased by 1.66 times and 0.73 times, respectively. The corrosive decomposition of minerals can improve the complexity of microscale or nanoscale pores and enhance the capacity of gas transportation from shale matrix to fractures. The oxidative decomposition of organic matter can transform the methane in organic matter from a dissolved or adsorbed state to a free state and generate more gas-flowing space in the shale matrix. The thermal stress fracturing in formation heat treatment can create complex nanopores and remove the retained fracturing fluid near the wellbore. The application of SCWT is expected to increase the efficiency of hydraulic fracturing, providing a new path to decrease the amount of retained material from hydraulic fracturing and increase the gas transportation capacity of shale formations.