润湿性制约下低阶煤不同煤岩组分甲烷解吸机制

The influence of low gas content and high water saturation of coal gradually becomes obvious with the penetration of the exploration and development of low-rank coalbed methane in China. Therefore, it is an important way to achieve high gas production of improving the desorption efficient of coalbed methane in the areas with low-rank coals. However, the heterogeneity of coal seam and the wettability differences between coal lithotypes make the micro-distribution of gas-water, interaction mechanism of coal-water-gas and energy transmission law during the methane desorption process in the coal more complex. In this project, the low-rank coals of Huanglong coal field in the Ordos Basin are chosen as a case study. The material composition, chemical structure, pore characteristics, wettability and effect of surfactant would be studied systematically. Thus, the key factors controlling wettability of different coal lithotypes would be identified based on multi-factor coupling analysis. Then the characteristics of methane adsorption-desorption of different coal lithotypes and the influence of wettability would be studied to reveal the interaction mechanism of coal-water-gas and energy transmission law during methane desorption restricted by the wettability. Finally, the methane desorption process in different coal lithotypes and anisotropic coals would be simulated with different conditions of water covering and their physical models of methane desorption would be established based on the simulation results. This research can improve the understanding of wettability and methane desorption mechanism of low-rank coals and promote the high efficient development of low-rank coalbed methane.

随着我国低煤阶煤层气勘探开发的深入，低含气量和含水性问题逐渐凸显，促进煤层气高效解吸成为低阶煤地区获得高产的重要途径。煤层具有很强的非均质性，不同煤岩组分润湿性差异致使煤层内部气水微观分布、煤-水-气相互作用机制及解吸过程的能量传递规律更加复杂。本项目拟以鄂尔多斯盆地黄陇煤田低阶煤为研究对象，系统研究不同煤岩组分的物质组成、化学结构、孔隙特征、润湿性及表面活性剂的影响，通过多因素耦合分析明确不同煤岩组分润湿性的关键控制因素；开展不同煤岩组分甲烷吸附解吸特征及润湿性作用机理研究，基于吸附势和量子化学理论，揭示润湿作用下甲烷解吸过程煤-水-气相互作用机制和能量传递规律；开展不同覆水条件下各煤岩组分及非均质煤层甲烷解吸过程模拟，建立润湿性制约下不同煤岩组分及非均质煤层甲烷解吸物理模型。本项目研究对深化低阶煤润湿性及煤层气解吸机理认识，实现低煤阶煤层气高效开发具有积极意义。

我国低阶煤分布广泛，低阶煤层气含量占总气量的的1/3左右。煤层的非均质性及其不同煤岩组分润湿性差异造成的煤储层内部气-水微观分布是制约煤层气高效解吸-产气的关键问题之一。本项目选择鄂尔多斯盆地黄陇煤田园子沟煤矿（YZG）和黄陵煤矿（HL）为研究对象，通过低阶煤不同煤岩组分物质组成与化学结构测试、孔隙结构多尺度表征，润湿性及甲烷吸附解吸实验。分析了物质组成和煤的微观结构特征（分子结构和孔隙结构）对润湿性的作用机理，进一步确定了低阶煤润湿性对甲烷吸附/解吸的影响。结果表明低阶煤不同煤岩组分中镜煤与暗煤的润湿性和甲烷吸附/解吸存在一定的差异。（1）在煤的物质组成、分子结构和孔隙结构特征的综合作用下，使得暗煤的润湿性优于镜煤，亲水性更好。究其原因是暗煤水分含量、灰分产率高于镜煤。镜煤芳香核缩合程度相对偏低、烷基侧链多而长；暗煤芳香核缩合程度程度相对偏高，烷基侧链少而短。镜煤含氧官能团含量多，但主要为醚氧基等非极性含氧官能团，暗煤中酚羟基、羧基和羰基等极性集团含量相对较高。此外，镜煤微孔隙发育、比表面越大，分形维数大，表面相对粗糙，暗煤孔隙均一、表面相对光滑。（2）镜煤微孔隙发育，比表面积和体积大于暗煤，对甲烷的吸附量大于暗煤。暗煤大孔和介孔发育，孔隙的连通性好，有效孔隙度大，有利于甲烷的解吸-运移。水分的存在严重影响了甲烷的吸附量和解吸率，且对暗煤的影响程度严重。（3）四种表面活性剂均不同程度的降低煤-水接触角，改善了煤的润湿性。分析煤的NMR水分分布结果发现，非离子表面活性剂APG0810显著增加了煤的含水含量，但不利于水分的排出。阳离子表面活性剂（CTAC）和双离子表面活性剂（BS-12）通过改善煤的润湿性，使水分进入到微孔隙，强化了甲烷和水分子的竞争吸附，促进水分对甲烷的置换解吸。在排水降压条件下，有利于水分的排出，降低了水锁堵孔，有利于甲烷的产出。最后根据不同煤岩组分孔隙结构及气水分布微观特征，阐明煤-水-气三相作用机制，建立润湿性制约下不同煤岩组分甲烷解吸模型。本项目取得的研究成果对深化低阶煤润湿性及煤层气解吸机理认识，为低煤阶煤层气高效开发提供了理论依据，具有积极的现实意义。