Characteristics of water migration during spontaneous imbibition in anisotropic coal

Abstract

Spontaneous imbibition is a process of effectively wetting coal pores, which can improve wetting uniformity. Therefore, spontaneous imbibition is critical for outburst, dust and rockburst preventions. Due to the anisotropy of coal, water injected into the borehole has different wetting characteristics along different bedding directions. To reveal the characteristics of water migration in coal samples with different bedding directions during spontaneous imbibition, T2 spectrum and imaging images measured by nuclear magnetic resonance are comprehensively analyzed. The fracture presents the effects of huffing and puffing during spontaneous imbibition. However, the effects of huffing and puffing gradually decrease with increasing bedding angle. Imbibition equilibrium time increases with increasing bedding angles. The wetting effect of pores, liquidity and wetting uniformity of water gradually become poor with increasing bedding angles. Spontaneous imbibition process presents the Lucas-Washburn model, and the imbibition curve can be divided into spontaneous imbibition, transition and diffusion stages. The wetting time perpendicular to bedding direction, layout of water injection boreholes and gas drainage boreholes perpendicular to bedding direction should be fully considered to prevent wetting blank areas. This research reveals the wetting behaviors of anisotropic coal during imbibition and provides guidance for layout and optimization of coal seam water injection boreholes.