1. Mining Technology Institute,Taiyuan University of Technology,Taiyuan　 030024,China; 2. College of Mining Engineering,Taiyuan University of Technol-ogy,Taiyuan　 030024,China

甲烷（CH4）在煤体中的流动包含“渗流—扩散—吸附/解吸”3个环节,相比粉状煤,采用块状煤体进行CH4吸附/解吸实验能够更有效地表征煤层中气体的流动状态。为此,依托渭北煤田韩城矿区煤样,利用自行设计的块煤吸附/解吸实验装置,研究了低压下块状同体积原生结构煤、碎裂煤和糜棱煤的CH4等温吸附/解吸特性;采用显微CT和扫描电镜分析了3种煤样的孔裂隙结构和显微构造,探讨了煤体结构对CH4吸附/解吸的影响。结果表明:不同煤体结构煤的CH4吸附/解吸特性有显著差异。结构致密的原生结构煤,孔隙度较低,导致CH4吸附/解吸平衡时间长,吸附量低,解吸率低;相比原生结构煤,脆性变形碎裂煤张裂隙发育且相互贯通,孔隙度变大,连通性好,导致CH4吸附/解吸平衡时间变短,吸附量升高,解吸率增大;韧性变形糜棱煤孔隙数量虽增多,但裂隙被揉皱闭合,形成孤立分布的孔隙结构,渗透性变差,导致CH4吸附/解吸平衡时间最短,解吸速率最快,说明大多数CH4仅吸附在块煤内构造变形作用下形成的粒间孔隙中。可知,碎裂煤储层是煤层气开发的有利区域;而致密原生结构煤和糜棱煤储层可尝试通过多尺度压裂、注热等技术手段实施储层改造以增加煤体裂隙通道,达到气井增产增效的目的。

The adsorption / desorption experiment of bulk coal sample can be more effective to characterize the flow state of methane (CH4 ) in coal seams compared to powder coal sample,since CH4 flow through a coal seam consists of fluid flow,diffusion and adsorption / desorption process. Thus,the low-pressure CH4 adsorption / desorption properties of bulk primary coal ( PC), cataclastic coal ( CC) and mylonitic coal ( MC ) with identical volume collected from Hancheng Mine,Weibei coalfield were analyzed using self-designed adsorption / desorption apparatus of bulk coal. In combination with micro-focus CT and scanning electron microscope images,the influence of coal-body structure on CH4 adsorption / desorption behavior was discussed. The results indicate that the obvious difference can be observed in coals with different coal-body structures. Long CH4 adsorption / desorption equilibrium time,small adsorption capacity and low desorption rate were recorded in PC due to its dense structure and low porosity. In comparison with PC,a shorter adsorption / desorption equilibrium time,higher adsorption capacity and faster desorption rate were occurred ow- ing to developed and connected fracture system and increased porosity in CC under brittle tectonic stress. Under duc- tile deformation,the coal composition of MC was folded and concomitant with increased pore number and closed frac- ture,which induced isolated pore structure and poor permeability. These characteristics result in the shortest adsorp- tion / desorption equilibrium time and the fastest desorption rate,indicating most of CH4 in bulk MC may merely adsorb on inter-granular pores formed during deformation process. Therefore,the CC reservoir is a favorable area for CBM de- velopment. Nonetheless,for both PC and MC reservoirs,the increase in the well yield and efficiency can be achieved through reservoir reformation by means of multi-scale fracturing,heat injection and other techniques which can increase the channels within coal fracture.

KANG Zhiqin,LI Xiang,LI Wei,et al. Experimental investigation of methane adsorption / desorption behavior in coals with different coal- body structure and its revelation[J]. Journal of China Coal Society,2018,43(5):1400-1407.