Towards A hydrogen economy: Understanding pore alterations in the context of underground coal gasification

Underground coal gasification (UCG) is gaining significant attention worldwide as a promising clean energy solution, particularly in conjunction with hydrogen production, amidst the global shift towards a hydrogen-based economy. However, existing research on hydrogen-oriented underground coal gasification (HUCG) has primarily emphasized hydrogen generation and syngas production optimization, neglecting a comprehensive analysis of pore space and permeability changes surrounding the cavities during water injection. To address this gap, we conducted a study to elucidate the alterations in pore structure of the surrounding coal seam during cavity development within the HUCG framework. Utilizing a large-scale 3D UCG model with a water injection well, we examined key parameters including temperature, porosity, permeability, and water saturation at various grid points around the cavity. Our modeling outcomes reveal that water injection influences both the cavity's development trajectory and coal pore characteristics, indicating a strong interplay between hydrological and physiochemical processes in UCG. Additionally, analysis of water saturation curves validates sensible injection rates for feasible HUCG implementation. This work provides important insights into the changes in coal morphology during hydrogen-oriented underground coal gasification, offers theoretical support for scaling up hydrogen production and advancing the development of a hydrogen-centric clean energy system. It contributes to the global shift towards a more diversified and sustainable hydrogen-based energy framework, accelerating political decision-making and technological progress. • A large-scale deep coal seam model with properties of the Santanghu Basin in Xinjiang, China, was constructed. •Key parameters were comprehensively investigated for insight into the evolution of coal seam pore structure around cavities. •Interplay between hydrological and physiochemical processes in UCG were analyzed systematically. •Validated reasonable injection rates for feasible HUCG implementation. •Revealed the influence of water injection on the morphological development of cavities.