超临界CO2强化页岩气开采与地质封存的多尺度多物理场耦合数值研究

As an emerging technology of carbon dioxide utilization and storage, supercritical CO2 enhancing natural gas recovery in shale is receiving much attention. Due to the complexity of shale structure, the understanding of transport and CO2 storage mechanism in shale is very limited. This project focuses the core issue of CO2 efficient displacement of natural gas in shale, molecular dynamics (MD) simulation and lattice Boltzmann method (LBM, a mesoscopic approach), have been employed to investigate the transport and CO2 storage mechanism for CO2 displacement of natural gas in shale. A multi-scale and multi-physics model, i.e., taking account of adsorption/desorption, diffusion, geochemical effects and shale matrix deformation in shale, is proposed. Furthermore, advanced techniques of digital core and CUDA-GPU parallel computing for LBM are utilized in the model. The interactions between CO2 and natural gas in shale are investigated in depth. The effects of adsorption/desorption, diffusion and shale matrix deformation on permeability are analyzed. Meanwhile the effects of shale structure, parameters of injected CO2 and geochemical effects on transport mechanism and CO2 storage are discussed. The aim of the present project is to reveal the transport and storage mechanism of CO2 displacement of natural gas and lay a theoretical foundation for CO2 enhanced natural gas recovery as well as CO2 geological storage in shale.

超临界二氧化碳强化页岩气开采，作为CO2资源化利用与地质封存一体化的新兴技术，日益受到重视。但由于页岩结构的复杂性，我们对其内部微观运移及封存机理的理解并不十分清晰。本项目围绕CO2高效置换页岩气这一核心问题，采用基于微观尺度的分子模拟(MD)与介观尺度的格子Boltzmann方法(LBM)，对页岩储层中CO2驱页岩气的微观运移与封存机理进行数值研究。提出建立页岩储层内考虑CO2驱页岩气的吸附/解吸、扩散、反应及岩石变形的多尺度多物理场耦合数值模型，并将模型结合数字岩心技术及LBM的CUDA-GPU并行计算技术，考察页岩储层内CO2与页岩气的相互作用机理，分析吸附/解吸、扩散及岩石变形等对渗流规律的影响，探究储层结构、CO2注入参数、反应过程等对微观运移规律及CO2地质封存效果的影响，揭示页岩储层内CO2驱页岩气及地质封存的微观传递机理，为页岩气高效开发和CO2地质封存提供理论依据。

利用超临界二氧化碳强化页岩气开采与地质封存过程中的微观运移机理非常复杂，本项目采用基于微观尺度的分子模拟(MD)与介观尺度的格子Boltzmann(LBM)方法，揭示了CO2强化页岩气开采过程中的微观传递机理。基于分子模拟，明晰了页岩储层受限空间内吸附气体以Langmuir单分子层吸附与微孔填充共同存在的微观机理，当气体处于页岩储层的微孔和小介孔内或超临界压力条件下，吸附气体会以两种吸附形式共同存在，微孔填充效应随着孔隙尺寸的降低和压力的升高而增大，吸附气体在大空间孔隙内主要以单分子层吸附为主。结合MD与LBM方法，将吸附、表面扩散等微观物理过程考虑到介观尺度传输模型中，构建了页岩气在页岩储层多孔结构内渗流过程的多尺度多物理耦合数值模型，获得了压力和孔径对页岩储层结构内气体运移机理的影响机制，研究结果表明在较小孔径的孔隙内，吸附气的表面扩散对气体流动有着重要的影响，随着孔径的增大，表面扩散的影响降低。基于OpenMP和CUDA-GPU并行计算技术，发展了LBM并行数值计算模型，对于三维物理问题，利用CUDA-GPU技术实现了300以上的加速比，提高了LBM方法对实际复杂物理问题的数值求解能力。