Multi-field coupling theory for modification of multi-scale pore-fracture structures of coal mass

LIANG Weiguo; CHEN Yuedu

doi:10.13225/j.cnki.jccs.2025.1246

Abstract：Multi-scale pore-fracture structures are widely occurred in coal reservoirs,and serving as the main spaces for gas storage and transport.Restructuring these multi-scale pore-fracture structures to enhance fluid adsorption and trans-port behaviors is critical to the successful implementation of in-situ modified mining technologies for the safe and effi-cient extraction of deep coal and coalbed methane resources.To address the limitations of conventional stimulation tech-niques and the unclear modification mechanisms,the multi-scale pore-fracture structure of coal mass,from nano-pores and micro-fractures to macro-fractures,and their impact on gas desorption,diffusion,and flow are analyzed.Two core modi-fication principles are proposed,one is enhancing desorption and transport by modifying the fluid occurrence state,and the other is improving the permeability by modifying the pore-fracture structure.Two multi-scale modification approaches are introduced,one is enhancing the desorption through competitive adsorption and thermal effects to reduce CH4 adsorption capacity,and the other is enhancing the permeability through dissolution-induced pore expansion and fracturing-induced fracture creation.Using supercritical CO2(ScCO2)as an example,the experimental results reveal the evolution of multi-scale pore-fracture structures in coal mass under ScCO2 injection,involving adsorption swelling,dissolution,mechanical weakening,and fracture generation.These processes collectively affect the adsorption and transport properties of coal mass.A multi-field coupling framework is established to describe mass transfer across scales,and porosity-permeability evolution.This work provides a theoretical foundation for targeted reservoir modification to enhance permeability,and CO2 geological storage in deep coal seams.