Research progress micro effect of water on coalbed methane adsorption/desorption

Water (moisture) is the key factor restricting the adsorption / desorption of coalbed methane (CBM). Influenced by the multi-pore structure of coal reservoir and the wetting difference of coal compositions, the coal-water-methane interface interaction result in the mutual excitation and restriction between CH₄ and H₂O in the process of CBM production. By comprehensively combing the research progress and frontier understanding of the adsorption/desorption effect of water on CBM, the internal relationship between water and the micro effect of CBM adsorption / desorption were analyzed from three aspects: the water occurrence state of coal reservoir, the micro action mechanism of coal-water interface and the influence of water on methane adsorption / desorption. The research showed that the pore structure and water occurrence state of coal reservoir are complicated. Based on the interface between coal and water and pore structure characteristics, coal reservoir water can be divided into three main types: bound water, irreducible water and free water. The inhibition mechanism of methane adsorption by different types of water is different, and the degree of influence on low-rank coal is serious. Water phase change has become the core affecting methane desorption-transport. Water vapor molecules replace adsorbed methane through competitive adsorption. Liquid water blocks pores and inhibits gas-water transport under the action of wettability and capillary force. In the process of surface CBM drilling and production, the action mechanism of water changes with the dynamic changes of reservoir temperature-pressure environment. Aiming at the status quo of unclear desorption mechanism and influence boundary of water on methane. Therefore, it was proposed to quantify the water content and distribution characteristics of the reservoir, enhance methane desorption and gas-water transport, improve the theory and model of methane adsorption / desorption, strengthen the theory and technology of water incentive and promote the increase of CBM production, further deepen the mechanism of the micro action of coal-water interface in the process of CBM desorption and transport, and promote the sustainable, stable and efficient exploitation of CBM.