Fracture and pore development law of coal under organic solvent erosion

Promoting fracture development of deep low-permeability coal seams is one of the necessary means to improve the efficiency of coalbed methane extraction. Organic solvent erosion is an efficient method to promote fracture and pore development in coal. However, the law of fracture and pore development in the process of solvent erosion has not been clarified yet. In this study, the law was discussed from four aspects, namely macro-fracture, micro-fracture, internal fracture and pore. The results show that organic solvent treatment is pretty effective in promoting the fracture and pore development. After solvent treatment, soluble molecules dissolve in the solvent and separate from coal to form the extract. Through the removal of soluble molecules, primary fractures and pores widen, and new fractures and pores develop in large numbers. Then, part of the insoluble coal becomes broken and falls off, forming the abscission. Different solvents exert varying effects which are related to their extraction rates on coal. Under a high extraction rate, secondary fractures are distributed around the main fractures, and fractures are interconnected to form a complex fracture network. Finally, the effects of organic solvents erosion on coal were classified.