In-depth review of colloidal and interfacial fundamentals in fracturing development of deep coal seam methane.

Deep coal seam methane represents a significant global energy resource, but its efficient extraction requires specialized fracturing technologies that address the unique characteristics of coal formations. This review provides a comprehensive examination of the fundamental colloidal and interfacial phenomena governing fracturing processes in deep coal seam methane development, with particular emphasis on the behavior of methane-water interfaces, the colloidal science of fracturing fluids, and transport mechanisms at the pore scale. The distinct properties of methane-water interfaces under confinement in coal micropores are analyzed, revealing how surface heterogeneity, temperature, pressure, and salinity influence interfacial tension, wettability, and fluid distribution. The extreme conditions of deep coal seams, characterized by high pressures (10-30 MPa) and elevated temperatures (>80 °C), significantly alter these interfacial dynamics compared to conventional reservoirs. The review explores the complex rheological behavior and stability mechanisms of foam-based fracturing fluids, including the roles of liquid drainage, coarsening, and bubble coalescence in determining foam performance under reservoir conditions. Special attention is given to surfactant molecular design, synergistic formulations, and the emerging field of viscoelastic surfactants that offer enhanced stability and rheological control. These formulations must be specially designed to withstand the extreme pressure-temperature regimes of deep coal seams while mitigating the swelling and strain characteristics unique to coal matrices. The colloidal aspects of proppant transport and placement in coal fractures are examined, highlighting the importance of proppant-fluid interactions and specialized lightweight materials for maintaining fracture conductivity. This review provides fundamental insights for developing next-generation fracturing technologies that enhance methane recovery in deep coal seam operations.