Self-supporting conductivity in shallow and ultra shallow shale reservoirs: Under hydraulic, CO2 and Sc-CO2 fracturing

Abstract

To study the differences in self-supporting conductivity among fractures obtained by hydraulic fracturing, CO2 fracturing, and Sc-CO2 (Supercritical carbon dioxide) fracturing, laboratory large-scale fracturing experiments and conductivity tests were carried out. To simulate the reservoir conditions as realistically as possible, the rock slabs used in the conductivity tests were all cut from the samples after fracturing experiments. Before a conductivity test, the fracture surfaces of each rock slab were digitized by laser scanning and 3D reconstruction technology. The JRC of each rock slab is calculated by using the point cloud data. Then, the self-supporting conductivity of each rock slab was tested under different conditions, and a relationship between the JRC, closure stress and sliding displacement and the self-supporting conductivity of fractures obtained by different fracturing techniques was analyzed. The experimental results show that: The JRC of the fractures obtained by Sc-CO2 fracturing is higher than that of CO2 fracturing. Moreover, the JRC of fractures in hydraulic fracturing is the lowest among the three fracturing technologies. The self-supporting conductivity of the fractures has a positive correlation with their JRC value. Compared to hydraulic fracturing and CO2 fracturing, the fractures obtained by Sc-CO2 fracturing have significant advantages in self-supporting conductivity regardless of slip displacement and closure stress.