Characteristics of water occurrence in coalbed methane reservoir

The presence of water, competing with methane for the space, weakens the ability of methane adsorption and diffusion in coal dramatically. The study on the occurrence of water in coal has direct effects on coalbed methane exploitation. In this study, NMR technology was used to obtain water vapor adsorption curves, moreover, the surface adsorption, water cluster formation and pore filling of water in coal pores of coal samples were characterized. Meanwhile, the method based on NMR was first used to quantify the water in different occurrence state in coal pores. The results show that modified BET model can not fit the data in all the pressure history of high rank coal with well-developed micropores and mesopores. Moreover, for pores in high-rank anthracite coal, adsorption water is mainly the indirect adsorption water, and for pores of low-rank bituminous coal, the proportion of direct adsorption water is 50%.