Experimental study on shale fracturing enhancement by using multi-times pulse supercritical carbon dioxide (SC-CO2) jet

Supercritical Carbon Dioxide (SC-CO2) fracturing can increase shale gas production and reduce carbon dioxide (CO2) emission. In order to enhance shale fracturing, a new method of multi-times pulse SC-CO2 jet fracturing is proposed and comprehensively studied. The results demonstrate there are more initiation positions and more complex fracture network after pulse SC-CO2 jet fracturing due to strong impingement and pressurization. Furthermore, three types of main fracture and four types of fracture branch are observed. The main fractures mostly initiate from perforation and propagate with irregular path to the specimen edge. CO2 absorption and fracture volume increase 77.72% and 2283%, respectively, more than that of single-pulse SC-CO2 jet fracturing. The comparison indicates that SC-CO2 creates more complex fracture morphology, larger fracture volume and CO2 absorption than that of water. Moreover, the effect of influential factors, including pulse jet frequency, pulse jet pressure and pulse jet distance, are discussed thoroughly. Thus, this study provides a method of jet fracturing enhancement, and is instructive for understanding and tackling pulse jet fracturing issue related to CO2 utilization and fracturing of shale reservoir.