Multiscale pore structural alteration in gas shale by supercritical water stimulation

Abstract

Hydraulic fracturing can induce high conductive fracture networks to stimulate shale gas well production. Large amounts of fracturing fluid generally retained in shale matrix after hydraulic fracturing will limit the shale gas well production. Reusing retained fracturing fluid by in-situ transformed into supercritical water (SCW) via formation heat treatment (FHT) is a state-of-the-art method to improve the shale gas well production by further altering shale multiscale pore structure. In this study, the changes in shale multiscale pore structure was visually and quantitatively characterized. The pore volume with a size range of 2 nm–5000 nm increased significantly. Inducing intragranular dissolution pores, pyrite dissolution pores, interparticle dissolution pores, and hydrothermal fractures stimulated the multiscale pore structure alteration during supercritical water stimulation (SCWS). Additionally, the advantage of SCWS in altering shale pore structure was systematically summarized, including further extend the hydraulic fracturing stimulation scale, enhancing multiscale shale gas flow capacity and ultimately improving well production. This work sheds light on the influence of supercritical water stimulation on the pore structure evolution in shale matrix, which is expected to be an innovative method for increasing the estimated ultimate recovery of a shale gas reservoir.