Multifactor Evolution and Carbon Sequestration Effect of Coal Pore Structure during CO2 Storage in a Coal Mine Goaf Environment

Abstract

Excessive greenhouse gas emissions, primarily CO2, are a principal cause of global warming. China’s extensive abandoned mines and goafs present a unique opportunity for CO2 storage, offering a dual benefit of reducing emissions and repurposing mine assets. This study explores the intricate fluid–solid interactions among CO2, H2O, and coal matrices, which significantly alter the coal’s pore structure and surface chemistry, impacting carbon sequestration efficacy. Utilizing coal samples from the 4-2 seam of Huangling’s No. 1 mine, Shaanxi, China, experiments simulated goaf conditions to examine CO2–H2O–coal interactions. Findings indicated that CO2–H2O exposure promotes metal cation dissolution and carbon fixation, favoring CO2 storage. Changes in coal’s mineral and organic components were noted, intensifying with reaction magnitude. Postreaction increases in pore volume, porosity, and fractal dimension suggest enhanced structural complexity due to matrix swelling and mineral dissolution-precipitation. A conceptual model of coal pore evolution under CO2–H2O influence is proposed, elucidating pore characteristic evolution mechanisms and the CO2 storage process’s impact on sequestration in goafs. This research aims to clarify CO2–H2O interaction mechanisms, assess storage safety, and support engineering projects targeting CO2 sequestration in abandoned mining sites.