Abstract:

In order to deeply understand the water transport characterizing in the coal body of high-rank coal during the process of water injection in coal seams, we took the high-rank coal of Jiaozuo Zhongmacun mine as the research object, and used the LNMR equipment to test the NMR spectra of the coal samples at different immersion times in the process of negative-pressure immersion test and isothermal wettability test. Combined with the quality change of the coal samples during the process of negative-pressure immersion, the experimental conditions necessary for the preparation of the saturated coal samples were obtained. Combined with the mass change of the coal samples during the process of isothermal wettability, from the microscopic level, the distribution characteristic of the water into the coal body, and the changing rules of the moisture content and the degree of saturation of the samples in the course of the wettability process of the coal samples were analyzed quantitatively. The results show that the water can infiltrate into the coal body under the action of capillary force with the minimum pore size corresponding to the NMR relaxation time of 0.014 ms. The water enters into the coal body in the order of larger pore→small pore→micro pore, and reaches the saturation state in the order of micro pore→small pore→larger pore. The overall water content saturation of the tested coal samples is almost the same at the same wetting time, although the water content is different. There is a quantitative relationship between the overall water saturation of the coal sample and the 0.5 power of the wetting time.

Key words: high-rank coal, wetting process transport characteristic, low-field nuclear magnetic resonance (LNMR), water saturation