Xiao Cangyan, Han Donglin, Zhang Junjian, Chen Shuzhao, Qin Zhenyuan, Vandeginste Veerle
School of Transportation Engineering, Jiangsu Vocational Institute of Architectural Technology, Xuzhou 221116, China.
College of Earth Sciences & Engineering, Shandong University of Science and Technology, Qingdao 266590, China.
ACS Omega. 2024 Jul 16;9(30):33279-33292. doi: 10.1021/acsomega.4c05179. eCollection 2024 Jul 30.
Considerable variations in microscopic and industrial components (ash, moisture, volatile matter, etc.) have been reported within identical coal seams. These disparities in coal quality and pore structure within the same coal seam profoundly affect the drainage of deep coalbed methane (DCBM). This study focuses on 22 coal samples collected from two wells in the Benxi Formation of the central and eastern parts of the Ordos Basin. First, the coal facies were determined for all samples using submicroscopic components, and then, the adsorption pore and seepage pore structures were studied through CO/N adsorption and mercury intrusive tests. Subsequently, the study delves into the correlation between coal rank, coal facies, and the distribution of the pore structures across various pore sizes, elucidating the primary controlling factors influenced by coal rank and coal phase. The results are as follows: (1) For a given coal seam, exhibits minimal variation among the samples, which suggests is not the primary factor affecting pore structure. Conversely, the ash content occupies the pore space, thereby revealing a negative correlation between the ash content and adsorption pore volume (PV). (2) On the basis of the texture preservation index (TPI) and gelatification index (GI), coal facies were classified into moist forest swamp facies (type A), moist herbaceous swamp facies (type B), and water-covered herbaceous swamp facies (type C). Type A is characterized by higher TPI, lower GI, and ash content, whereas type C exhibits lower TPI, higher GI, and ash content. (3) Type A samples, with the lowest ash content, display larger PV and specific surface area (SSA) compared with type B, while type C has the lowest values. Type C, with the highest vitrinite content, predominantly consists of semibright and bright coal, prone to microcracks, which results in a higher seepage PV compared with types A and B. (4) The coal facies represent variations in ash content and microscopic components, which significantly impacts both adsorption and seepage pores. Moist forest swamp facies samples are characterized by micropore development and the highest content of adsorbed gas. Herbaceous swamp facies samples display macropore development and the highest content of free gas.
据报道，同一煤层内的微观和工业成分（灰分、水分、挥发物等）存在显著差异。同一煤层内煤质和孔隙结构的这些差异对深部煤层气（DCBM）的抽采有深远影响。本研究聚焦于从鄂尔多斯盆地中东部本溪组两口井采集的22个煤样。首先，利用亚微观成分确定所有样品的煤相，然后通过CO₂/N₂吸附和压汞试验研究吸附孔隙和渗流孔隙结构。随后，该研究深入探讨了煤阶、煤相以及不同孔径孔隙结构分布之间的相关性，阐明了受煤阶和煤相影响的主要控制因素。结果如下：（1）对于给定煤层，样品间挥发分含量变化最小，这表明挥发分不是影响孔隙结构的主要因素。相反，灰分占据孔隙空间，从而揭示了灰分含量与吸附孔隙体积（PV）之间呈负相关。（2）基于结构保存指数（TPI）和凝胶化指数（GI），煤相分为潮湿森林沼泽相（A 型）、潮湿草本沼泽相（B 型）和水淹草本沼泽相（C 型）。A 型的特点是 TPI 较高、GI 和灰分含量较低，而 C 型则表现为 TPI 较低、GI 和灰分含量较高。（3）灰分含量最低的 A 型样品与 B 型相比，显示出更大的 PV 和比表面积（SSA），而 C 型的值最低。C 型镜质体含量最高，主要由半亮煤和亮煤组成，容易产生微裂纹，与 A 型和 B 型相比，其渗流 PV 更高。（4）煤相代表了灰分含量和微观成分的变化，这对吸附孔隙和渗流孔隙都有显著影响。潮湿森林沼泽相样品的特征是微孔发育且吸附气含量最高。草本沼泽相样品表现为大孔发育且游离气含量最高。
