This work presents a hybrid discrete fracture-dual porosity model of compressible fluid flow, adsorption and geomechanics during CO2 sequestration in coal seams. An application of the model considers the influence of hydraulic fractures on CO2 transport and the stress field of the coal. The low initial permeability of coal is compounded by the injectivity loss associated with adsorption-induced coal swelling, which is recognised as the major challenge limiting CO2 sequestration in coal seams. In this model, the natural fracture network and coal matrix are described by a dual porosity model, and a discrete fracture model with lower-dimensional interface elements explicitly represents any hydraulic fractures. The two models are coupled using the principle of superposition for fluid continuity with a local enrichment approximation for displacement discontinuity occurring at the surface of hydraulic fractures. The Galerkin finite element method is used to solve the coupled governing equations, with the model being verified against analytical solutions and validated against experimental data. The simulation results show that the presence of a hydraulic fracture influences the distribution of gas pressure and improves the gas flow rate, as expected. The stress field of a coal seam is disturbed by CO2 injection, especially the vertical stress, and the presence of a hydraulic fracture leads to a reduction in stress with permeability recovery starting earlier.

中文翻译：

---

通过与注入井连接的增产裂缝提高煤层 CO2 注入能力的数值分析

这项工作提出了煤层中 CO2 封存过程中可压缩流体流动、吸附和地质力学的混合离散裂缝-双孔隙度模型。该模型的应用考虑了水力压裂对 CO2 输运和煤层应力场的影响。煤的低初始渗透率与吸附引起的煤膨胀相关的注入损失加剧，这被认为是限制煤层中 CO2 封存的主要挑战。在该模型中，天然裂缝网络和煤基质由双孔隙度模型描述，具有低维界面元素的离散裂缝模型明确表示任何水力裂缝。这两个模型使用流体连续性的叠加原理与发生在水力裂缝表面的位移不连续性的局部富集近似相耦合。Galerkin 有限元方法用于求解耦合控制方程，模型根据解析解进行验证，并根据实验数据进行验证。模拟结果表明，如预期的那样，水力压裂的存在影响了气体压力的分布并提高了气体流速。煤层的应力场受到 CO2 注入的干扰，尤其是垂直应力，水力压裂的存在导致应力降低，渗透率恢复开始较早。Galerkin 有限元方法用于求解耦合控制方程，模型根据解析解进行验证，并根据实验数据进行验证。模拟结果表明，如预期的那样，水力压裂的存在影响了气体压力的分布并提高了气体流速。煤层的应力场受到 CO2 注入的干扰，尤其是垂直应力，水力压裂的存在导致应力降低，渗透率恢复开始较早。Galerkin 有限元方法用于求解耦合控制方程，模型根据解析解进行验证，并根据实验数据进行验证。模拟结果表明，如预期的那样，水力压裂的存在影响了气体压力的分布并提高了气体流速。煤层的应力场受到 CO2 注入的干扰，尤其是垂直应力，水力压裂的存在导致应力降低，渗透率恢复开始较早。