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

Supercritical Carbon Dioxide (SC-CO 2) fracturing can increase shale gas production and reduce carbon dioxide (CO 2) emission. In order to enhance shale fracturing, a new method of multi-times pulse SC-CO 2 jet fracturing is proposed and comprehensively studied. The results demonstrate there are more initiation positions and more complex fracture network after pulse SC-CO 2 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. CO 2 absorption and fracture volume increase 77.72% and 2283%, respectively, more than that of single-pulse SC-CO 2 jet fracturing. The comparison indicates that SC-CO 2 creates more complex fracture morphology, larger fracture volume and CO 2 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 CO 2 utilization and fracturing of shale reservoir. The method of multi-times pulse SC-CO 2 jet fracturing is proposed, and comprehensive experimental studies are conducted. The multi-times pulse SC-CO 2 jet fracturing can cause more complex fracture morphology, larger fracture volume and CO 2 absorption than that of pulse water jet fracturing, due to its low viscosity, high diffusion and compressible characteristic of SC-CO 2. Image 1 • Multi-times pulse SC-CO 2 jet fracturing was firstly proposed and studied in our manuscript. • The fracture number and fracture tortuosity increase when jet pressure and jet frequency are larger. • The multi-times pulse SC-CO 2 jet fracturing can cause more complex fracture morphology than that of water. • The frequency of pulse SC-CO 2 jet fracturing is important for the complexity of fracture. [ABSTRACT FROM AUTHOR]