Abstract: CO₂-enhanced coalbed methane (CO₂-ECBM) recovery and sequestration offers dual benefits of greenhouse gas mitigation and enhanced methane production, which is of significant strategic value for supporting China’s "dual-carbon" strategy and ensuring energy security. Multiphase and multicomponent fluid flow mechanisms constitute the theoretical foundation for overcoming the engineering bottlenecks of CO₂-ECBM, enabling efficient CO₂ injection, secure sequestration, and enhanced CH₄ production in coal reservoirs. This paper systematically elaborates on the multiphase and multicomponent fluid permeation mechanisms in CO₂-ECBM, along with the key influencing factors. It further reviews advancements in corresponding experimental methods, multiscale modeling and numerical simulation techniques, highlighting their practical applications in engineering field, while identifying current theoretical challenges and potential solutions. The research results show as follows. (1) Due to its microscopic-level competitive advantages including higher quadrupole moment, stronger adsorption heat, and smaller kinetic diameter, CO₂ preferentially occupies high-energy adsorption sites on the coal surface; fluid diffusion occurs through a coupled mechanism involving bulk diffusion, Knudsen diffusion, and surface diffusion; low-velocity non-Darcy flow is prevalent in coal reservoirs, while fluid continuity processes are characterized by multiphysics, multiphase, multicomponent, and multiple scales. The sequential coupling of the adsorption-diffusion-seepage processes is critical to ensuring displacement efficiency. (2) The pore-fracture structure is a critical factor influencing multiphase and multicomponent fluid flow. Meanwhile, the cooperative transport mechanisms within multiscale pores and fractures and their spatial connectivity significantly influence fluid migration processes. The Knudsen number is an important parameter for characterizing flow regimes. CO₂ injection causes matrix swelling and an increase in effective stress, leading to a reduction in permeability. Geochemical effects, such as mineral dissolution, enhance pore permeability and facilitate fluid migration. Injection pressure and rate are key engineering parameters that control the advancement of the flow front, and the proper configuration of these parameters is essential for improving displacement efficiency. The coupled interactions and competitive relationships between multiple physical fields also have a significant impact on multiphase and multicomponent fluid migration. (3) Characterization of coal pore-fracture structures and fluid occurrence primarily relies on observation techniques, radiation detection techniques, gas adsorption and fluid intrusion methods, and integrated multiscale approaches. Adsorption-desorption behaviors are revealed through isothermal and competitive adsorption experiments. Diffusion-seepage experiments, supported by nuclear magnetic resonance and computed tomography (CT), provide dynamic insights into fluid migration under reservoir conditions. Displacement-drainage-storage physical simulations elucidate the key mechanisms of pore structure evolution and permeability changes under geological conditions. (4) Multiscale modeling and numerical simulations enable the establishment of a molecular-pore-engineering hierarchical research framework. Molecular modeling and dynamic simulations reveal the micromechanisms for the competitive adsorption and diffusion of CO₂ and CH₄. Pore-scale techniques, such as pore network modeling (PNM) and computational fluid dynamics (CFD), combined with X-ray computed tomography (X-CT) and focused ion beam-scanning electron microscopy (FIB-SEM), enable the analysis of fluid flow and mass transfer in complex pore networks. Core-scale numerical simulations serve as a crucial link between experimental results and field applications, while engineering-scale coupled multiphysics simulations provide dynamic assessments of injection-production processes, storage capacity, and safety. This integrated approach offers valuable support for well pattern optimization and parameter design. Currently, research into multiphase and multicomponent flow mechanisms in CO₂-ECBM is transitioning from single-process analyses to an integrated approach involving multiple technologies and scales. Future research should focus on key scientific issues such as pore-fracture evolution, multiphase-multicomponent fluid coupling, and phase transition mechanisms. Efforts should focus on experimentally replicating in-situ reservoir conditions, developing dynamically calibrated three-dimensional geological models, and integrating artificial intelligence and big data to achieve breakthroughs in critical technologies. This approach facilitates comprehensive integration of theory, experiments, and simulations, ultimately enhancing the CO₂-ECBM displacement efficiency and ensuring storage safety.

Key words: CO₂-ECBM, multiphase and multicomponent fluids, fluid continuity process, adsorption-desorption, diffusion-seepage, numerical simulation

摘要： CO₂驱煤层气封存(CO₂-Enhanced Coalbed Methane,CO₂-ECBM)兼具温室气体减排与煤层气增产的双重效益,在支撑国家"双碳"战略目标实现和维护能源安全方面具有重要战略价值。多相多组分流体渗流机理是突破CO₂-ECBM工程技术瓶颈,实现煤储层CO₂高效注入、高效封存与CH₄高效增产的理论基础。系统阐述了CO₂-ECBM多相多组分流体渗流机理及关键影响因素,探讨了多相多组分流体渗流机理的实验研究方法和多尺度建模与数值模拟技术进展及其在工程实践中的应用,明晰了当前理论研究存在的问题及可能的解决途径。研究结果表明:①CO₂凭借更高的四极矩、吸附热以及较小的动力学直径等竞争吸附微观优势,能够优先占据煤表面的高能吸附位点;流体扩散表现为体相扩散、克努森扩散与表面扩散的多机制耦合;煤储层普遍存在低速非达西流,而流体连续性过程表现出多物理场、多相态、多组分和多尺度的特征,吸附-扩散-渗流环节的有序衔接是保障驱替效率的关键。②孔隙-裂隙结构是影响多相多组分流体渗流的重要因素,多级孔隙-裂隙的协同运移机制及其空间连通性影响流体运移过程;克努森数是表征流态特征的重要参数,CO₂注入引起基质膨胀与有效应力增加导致渗透率下降;地球化学效应通过矿物溶蚀提 升了孔渗性,促进了流体的运移;注入压力与速率是调控渗流前沿推进的关键工程参数,合理配置工程注入参数是实现驱替效率提升的关键;多场耦合作用及其竞争关系也对多相多组分流体运移具有重要影响。③煤层孔隙-裂隙结构与流体赋存状态的表征主要依赖观测法、射线探测法、气体吸附与流体贯入法及多尺度联合观测;通过等温吸附与竞争吸附实验可揭示吸附-解吸行为;扩散-渗流实验辅以核磁共振与计算机断层扫描(CT)等技术可动态反映地层条件下的流体运移过程;置换-驱替-封存物理模拟实验则揭示了地层条件下孔渗结构演化及渗透率变化的关键机制。④多尺度建模与数值模拟可以构建分子-孔隙-工程层级的研究体系,大分子建模与动力学模拟可以揭示CO₂-CH₄竞争吸附与扩散微观机理,孔隙尺度孔隙网络模型(PNM)构建、计算流体力学法(CFD)等方法结合X射线计算机断层(X-CT)成像与聚焦离子束扫描电子显微镜(FIB-SEM)等技术可解析复杂孔喉网络中的流动与传质规律,岩心尺度数值模拟是连接实验与工程应用的关键,工程尺度多场耦合模拟则实现了注采过程、封存容量与安全性的动态评价,可以为井网优化与参数设计提供支撑。当前CO₂-ECBM多相多组分渗流机理研究正由单过程解析发展为多技术、多尺度一体化研究,未来应聚焦孔隙-裂隙演化、多相多组分流体耦合与多相态转化等关键科学问题,推动实验条件向储 层原位状态逼近,构建动态校正三维地质模型,并融合人工智能与大数据,实现关键技术突破,促进理论-实验-模拟的深度融合,从而提升CO₂-ECBM驱替效率与封存安全性。

关键词: CO₂-ECBM, 多相多组分流体, 流体连续性过程, 吸附-解吸, 扩散-渗流, 数值摸拟