Study on pore-crack evolution and connectivity of coal subjected to controlled electrical pulse based on CT scanning technology

Abstract

Controlled electric pulse (CEP) technology is a novel method for enhancing coal seam permeability. To study the pore-crack evolution and connectivity of the coal body by CEP, a self-built CEP cracking and enhancing permeability of coal rock test system was used to test five groups of coal samples under different breakdown voltages (BVs). We established a three-dimensional crack structure and equivalent pore network model for before and after penetration using high-precision micro-CT technology to quantitatively study the evolution and connectivity of the pore and crack structures of the coal body. The results showed that with rising BV, coal body crushing intensifies, leading to an increased cracking ratio and fractal dimension. This summarised the three stages of coal sample crushing by CEP. In addition, the proportion of larger equivalent pores and throat radii in the breakdown coal body was significantly increased compared to that of raw coal, and the connectivity structure was improved to different degrees compared to that of raw coal. Eventually, a three-dimensional crack network structure formed inside the coal samples, which was broken at both ends and complex in the middle, providing a transport channel for coalbed methane mining.