水分对煤层气吸附/解吸微观作用研究进展

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

水分是制约煤层气吸附/解吸的关键因素之一,受煤储层多元孔隙结构和煤岩组分润湿性差异影响,煤-水-甲烷界面作用导致煤层气产出过程中CH4与H2O相互激励、相互制约。立足于水分对煤层气吸附/解吸作用的研究进展与前沿认识,从煤储层水分赋存状态、煤-水界面微观作用和水分对甲烷吸附/解吸影响3个方面重点分析了水分与煤层气吸附/解吸微观效应之间的内在关系。研究认为煤储层孔隙结构及水分赋存状态复杂。以煤-水界面作用及孔隙结构特征为依据将煤储层水划分为结合水、束缚水和自由水3种主要类型,不同类型水分对甲烷吸附的抑制作用机制存在差异、且对低阶煤的影响程度严重。水分相态变化成为影响甲烷解吸-运移的核心,水蒸汽分子通过竞争吸附置换吸附态甲烷,液态水在润湿性和毛细管力作用下水锁堵孔、抑制气-水运移。在地面煤层气钻采过程中水分的作用机理随储层温度-压力环境动态变化而变化。针对水分对甲烷解吸作用机理不清、影响界限不明的现状,由此提出了量化储层水分含量及分布特征,增强甲烷解吸与气-水运移,完善甲烷吸附/解吸理论与模型,强化水分激励、促进煤层气增产4方面的科学问题及发展方向,进一步深化煤-水界面微观作用在煤层气解吸运移过程中的机理,促进煤层气持续稳定高效开发。

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 CH_(4) and H_(2)O in the process of CBM production.By comprehensively combing the research pro-gress and frontier understanding of the adsorption/desorption effect of water on CBM,the internal relationship between water and the mi-cro 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 struc-ture and water occurrence state of coal reservoir are complicated.Based on the interface between coal and water and pore structure charac-teristics,coal reservoir water can be divided into three main types:bound water,irreducible water and free water.The inhibition mechan-ism 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 competit-ive 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.