低阶煤储层吸附性能的水作用机制

The gas content of low rank coal seam in our country is generally low. And hydrogeology condition is one of the significant factors to determine low rank coalbed (CBM) methane accumulation effectively. It is mainly showed in that gas sorption capacity of coal reservoir influenced by medium environment of formation water, and the dynamic balance relationship of CBM adsorption-accumulation and solution-loss controlled by hydrodynamic conditions. The unclear understanding of mechanism of water controlling on methane adsorption capacity of low rank coal would negatively affect the optimization of low coal rank CBM enrichment area, and further the development progress. This project tends to choose the southern margin of Junggar basin as study area. On the basis of overall understanding of the structure development and the hydrology background of the low rank coal reservoirs, combining with the experiment tests and physical simulation methods, the project indicates the basic properties and adsorption characteristics of low rank coal, and mainly discusses the gas sorption capacity of low rank coal under different moisture content and salinity, and different hydrodynamic conditions. It finally reveals the mechanism of water influenced the gas adsorption capacity of low rank coal reservoir. Furthermore, the project preliminary discusses the influence of different hydrogeology conditions on low coal rank CBM accumulation in study area by analyzing the balance relationship of CBM adsorption-accumulation and solution-loss.

我国低阶煤储层含气量普遍较低，能否有效成藏受水文地质条件影响显著，主要体现在水介质环境对煤储层吸附性能的影响以及水动力条件制约下的煤层气吸附聚集—溶解逸散平衡关系。低煤阶煤层气吸附性能的水作用机制认识不清，将影响到低煤阶煤层气富集区的优选和开发进度。项目拟以准噶尔盆地南缘为研究区，在系统了解该区低煤阶储层发育的构造—水文地质背景基础上，采用实验测试、物理模拟等手段，阐明煤岩基本性质及其吸附特性，重点探讨不同含水率、不同矿化度以及不同水动力条件下低阶煤的吸附性能，揭示影响低阶煤储层吸附性能的水作用机制，进一步通过煤层气吸附聚集—溶解逸散平衡关系分析，初步探讨准南地区不同水文地质条件对低煤阶煤层气成藏的影响。

含气量是制约煤层气成藏的决定性因素，对于低阶煤而言尤为突出。低煤阶煤层含气量有限，煤中水分含量、水介质酸碱度、水矿化度以及水力交替作用强度造成的储层吸附性能变化对低煤阶煤层气聚集成藏显得尤为重要。项目以准噶尔盆地南缘低阶煤储层为研究对象，系统开展了不同水介质条件下低阶煤吸附性能及其水作用机理等研究内容，并结合准噶尔盆地南缘区域地质条件，综合分析了水文地质条件对低阶煤储层含气性的控制作用。结果表明：（1）准噶尔盆地南部中侏罗统西山窑组褐煤显微组分以腐植组为主，惰质组次之，壳质组含量最低，偶见腐泥组分。长焰煤和部分气煤有机显微组分以镜质组和惰质组为主，壳质组含量较少。灰分产率明显高于褐煤样品，而水分含量和挥发分产率明显偏低，这也是煤变质程度增高的直接结果。（2）随着煤中水分含量的增大，煤岩等温吸附曲线形态未发生明显变化，但煤的吸附量皆明显减小。含水率对褐煤影响较大，对长焰煤影响相对较小；随着矿化度的增加兰氏体积整体呈线性降低的趋势；随着水动力的冲洗和气体运移，煤层中吸附气含量将不断减少，影响煤层气的富集与保存。水动力条件频繁交替的情况下，煤层气不断解吸溶解于水中，破坏了煤层气藏原有的保存条件。（3）准南地区发育单斜、向斜、背斜以及复合褶皱等多种构造类型，具有不同的水动力场与煤层气富集条件。复合褶皱-向斜(12.30 m3/t)=简单向斜(11.33-11.91 m3/t)> 复合褶皱-背斜(7.09 m3/t)>单斜(2.32-3.23 m3/t)。研究成果对于丰富我国煤层气成藏动力学理论，揭示低阶煤煤层气成藏机理及指导低阶煤煤层气勘探开发部署等方面具有重要的理论意义和应用价值。