Experimental study on influence of high pressure water injection on coal pore structure

During high-pressure water injection process on coal seam, change laws of pore structure of coal seam were revealed, while the pore structure of coal s eam was an important influential factor to the gas adsorption and seepage of coal seam. With the methods of nuclear magnetic resonance experiment, permeability exp eriment and observing microfissuring through light microscope, the influence of high-pressure water injection on pore structure of coal seam was researched in micro pe rspective, which provided theoretical basis for high-pressure water injection technology of coal seam in micro perspective. It can be found from nuclear magnetic resona nce experiment that all pore volumes of different pore types of unit volume coal( 1 cm3) increase after high-pressure water injection, the mesopore has the smallest inc rement with the pore volume increasing by 0.73x 10-3cm3 averagely and the small-pore has the biggest increment with the pore volume increasing by 8.79x 10-3cm3 av eragely. Meanwhile, light microscope observation showed that the high pressure water injection was favorable for crack connection, new fractures forming and crack wi dth increasing, so as to increase the permeability of coal for 146% ~ 560%. Based on permeability analysis of the coal, it was concluded that large pore, which was the main methane flow path, was the major control factor of permeability and the secondary control factor was mesopore. The microspore and small pore contribute lttle to permeability and their main effects were adsorption and desorption of methane.