Ji Xiaofeng, Song Dangyu, Shi Wenfang, Li Yanfei
School of Energy and Materials Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, P. R. China.
Institute of Resource and Environment, Henan Polytechnic University, Jiaozuo 454000, P. R. China.
ACS Omega. 2021 Jul 14;6(29):19115-19126. doi: 10.1021/acsomega.1c02442. eCollection 2021 Jul 27.
To better understand the influence and control of nanopore characteristics on gas migration, three kinds of coal samples with different metamorphic degrees were selected for the experiments including high-pressure isothermal gas adsorption, low-pressure CO adsorption, and low-pressure Ar adsorption. The changes of the pore volume (PV) and specific surface area (SSA) of coal samples before and after adsorption-desorption were compared and analyzed. The adsorption data of all coal samples at a low pressure stage (<8 MPa) conformed to the Langmuir equation, and the adsorption capacity of powdered coal samples was higher than that of columnar coal samples. Some adsorption data deviated from the original fitting curve at a high pressure stage (>8 MPa), and this was the most remarkable in columnar coal samples. There was a positive correlation between the cumulative SSA of pores and adsorption capacity of coal samples. When the adsorption time was more than 10 min, the adsorption efficiency of 200 mesh coal samples from YJL was lower than those of 200 mesh coal samples from CZ and WY, which was due to the good development and connectivity of micro-fissures and nanopores in YJL coal samples. The pore size distribution of coal samples had changed after adsorption-desorption, and the cumulative deformation of the nanopore structure was anisotropic. As a result of the swelling or shrinkage deformation of the coal matrix, the PV and SSA with the same pore size presented many forms, such as almost unchanged, increased, or decreased. There are two types of deformation mechanisms: the whole collaborative deformation and partial deformation. Both gas adsorption and desorption can lead to the shrinkage or swell deformation of nanopores and fissures. In brief, the research provides theoretical and technical support for reservoir evaluation, fine drainage, and efficient development of coalbed methane.
为了更好地理解纳米孔隙特征对气体运移的影响及控制，选取了三种不同变质程度的煤样进行高压等温气体吸附、低压CO吸附和低压Ar吸附实验。对比分析了煤样吸附 - 解吸前后的孔隙体积（PV）和比表面积（SSA）变化。所有煤样在低压阶段（<8 MPa）的吸附数据符合朗缪尔方程，粉煤样的吸附能力高于柱状煤样。部分吸附数据在高压阶段（>8 MPa）偏离了原始拟合曲线，在柱状煤样中最为显著。煤样的孔隙累积比表面积与吸附能力呈正相关。当吸附时间超过10 min时，YJL的200目煤样的吸附效率低于CZ和WY的200目煤样，这是由于YJL煤样中微裂隙和纳米孔隙发育良好且连通性强。煤样的孔径分布在吸附 - 解吸后发生了变化，纳米孔隙结构的累积变形具有各向异性。由于煤基质的膨胀或收缩变形，相同孔径的PV和SSA呈现多种形式，如几乎不变、增加或减小。存在两种变形机制：整体协同变形和局部变形。气体吸附和解吸都会导致纳米孔隙和裂隙的收缩或膨胀变形。简而言之，该研究为煤层气储层评价、精细排采和高效开发提供了理论和技术支持。
