Coalbed methane is an important coal-associated resource, with abundant resource reserves and significant development and utilization value. Liquid nitrogen (LN₂) fracturing is an effective non-water technology for enhancing the gas flow in coal, which has a great prospect of application. Coal seam permeability is an important parameter for evaluating the recoverability of coal seams, while the permeability is mainly determined by the development of internal fractures. Considering the bituminous coal in the Xutuan Coal Mine of Anhui Province, China, the single and cyclic LN₂ fracturing experiments were carried out, and the evolution law of pore-fracture stracture and permeability characteristics of coal samples were studied. Firstly, the mechanism of LN₂ fracturing was analyzed, and the feasibility and present situations of LN₂ fracturing technology were summarized. Secondly, the mineral composition of experimental coal samples was determined by X-ray diffraction and semi-quantitative analysis was performed. The mercury intrusion pore measurement and computerized tomography technology were used to quantitatively characterize the increasing changes of coal pores and fractures after LN₂ fracturing. The fractal geometry and pore network model were applied to analyze the fractal characteristics, distribution of spatiality and connectivity of micro-fractures. Finally, the seepage experiment was carried out by the Gas Flow and Displacement Testing Apparatuus, which revealed the change law of coal permeability enhancement under single and cyclic LN₂ fracturing with different stress state.

 

暂无