College of Safety Science and Engineering, Liaoning Technical University, Fuxin, China.
Key Laboratory of Mine Thermodynamic Disaster and Control of Ministry of Education, Fuxin, China.
PLoS One. 2021 Jun 24;16(6):e0252277. doi: 10.1371/journal.pone.0252277. eCollection 2021.
The distribution of multiscale pores and fractures in coal and rock is an important basis for reflecting the capacity of fluid flow in coal seam seepage passages. Accurate extraction and qualitative and quantitative analysis of pore-fracture structures are helpful in revealing the flow characteristics of fluid in seepage channels. The relationship between pore and fracture connectivity can provide a scientific reference for optimizing coal seam water injection parameters. Therefore, to analyse the change in permeability caused by the variability in the coal pore-fracture network structure, a CT scanning technique was used to scan coal samples from the Leijia District, Fuxin. A total of 720 sets of original images were collected, a median filter was used to filter out the noise in the obtained images, and to form the basis of a model, the reconstruction and analysis of the three-dimensional pore-fracture morphology of coal samples were carried out. A pore-fracture network model of the coal body was extracted at different scales. Using the maximum sphere algorithm combined with the coordination number, the effect of different quantitative relationships between pore size and pore throat channel permeability was studied. Avizo software was used to simulate the flow path of fluid in the seepage channels. The change trend of the fluid velocity between different seepage channels was discussed. The results of the pore-fracture network models at different scales show that the pore-fracture structure is nonuniform and vertically connected, and the pores are connected at connecting points. The pore size distribution ranges from 104 μm to 9425 μm. The pore throat channel length distribution ranges from 4206 μm to 48073 μm. The size of the coordination number determines the connectivity and thus the porosity of the coal seam. The more connected pore channels there are, the larger the pore diameters and the stronger the percolation ability. During flow in the seepage channels of the coal, the velocity range is divided into a low-speed region, medium-speed region and high-speed region. The fluid seepage in the coal seam is driven by the following factors: pore connectivity > pore and pore throat dimensions > pore and pore throat structure distribution. Ultimately, the pore radius and pore connectivity directly affect the permeability of the coal seam.
煤岩中多尺度孔隙和裂隙的分布是反映煤层渗流通道流体流动能力的重要基础。准确提取和定性定量分析孔隙-裂隙结构有助于揭示渗流通道中流体的流动特征。孔隙与裂隙连通性的关系可为优化煤层注水参数提供科学依据。因此，为分析煤体孔隙-裂隙网络结构变化引起的渗透率变化，采用 CT 扫描技术对阜新雷家地区煤样进行扫描。共采集 720 套原始图像，对所得图像进行中值滤波去除噪声，形成模型基础，对煤样的三维孔隙-裂隙形态进行重建和分析。提取出不同尺度的煤体孔隙-裂隙网络模型，采用最大球算法结合配位数，研究不同孔径与孔隙喉道渗透率定量关系的影响。利用 Avizo 软件模拟渗流通道中流体的流动路径，讨论不同渗流通道间流体速度的变化趋势。不同尺度的孔隙-裂隙网络模型结果表明，孔隙-裂隙结构不均匀且呈竖向连通，孔隙在连通点处相互连接。孔隙尺寸分布范围为 104μm9425μm，孔隙喉道长度分布范围为 4206μm48073μm。配位数的大小决定了煤体的连通性，进而决定了孔隙率。连通的孔隙通道越多，孔径越大，渗透能力越强。在煤的渗流通道中流动时，速度范围分为低速区、中速区和高速区。煤层流体渗流受以下因素驱动：孔隙连通性>孔隙和喉道尺寸>孔隙和喉道结构分布。最终，孔隙半径和孔隙连通性直接影响煤层的渗透率。
