Applications and advances in characterizing pore-interface structures in coal using small angle scattering technology: A review.

The multiscale pore-fracture interface in coal forms the fundamental physical basis governing both coalbed methane (CBM) storage-transport behavior and CO2 geological storage efficiency. This review systematically discusses the principle of small angle scattering (SAS) technology in the analysis of coal matrix pore interface, and focuses on the frontier application of coal-fluid interface in terms of geometry, physicochemical properties and dynamic evolution. Results indicate that SAS can nondestructively quantify the entire pore system, including closed pores. Moreover, the predominance of closed pores in quantity and distribution is strongly affected by coal type and tectonic stress. The unique advantages of in-situ SAS technology in real-time tracking of interface dynamics and complex response mechanisms (such as expansion/contraction, pore damage and structural rearrangement of coal matrix under external fields such as gas adsorption, stress loading and pyrolysis) are analyzed. Through the interface fractal, SAS provides key parameters for quantitative description of interface complexity and its internal correlation with coal chemical composition. The application of "contrast-matching small-angle neutron scattering" (CM-SANS) in visualization of fluid accessibility, the key role of time-resolved small angle scattering technology in capturing instantaneous dynamic structural response of rock mass, and the cutting-edge technology of multi-scale and multi-dimensional data fusion are systematically discussed. The purpose of this review is to provide robust micromechanical support for understanding the coal-fluid interaction, thereby promoting innovation in energy and environmental engineering technologies such as CBM efficient development and carbon capture, utilization, and storage (CCUS).