基于三维数字岩心的流动-传热传质-化学反应耦合的直接数值模拟研究

Important geoscience and environment applications，such as the unconventional oil and gas recovery, CO2 sequestration, environmental soil remediation, can be better understood in the context of the coupled fluid/heat/mass transfer and chemical reactions in the subsurface environment. The multiple physicochemical processes are highly influenced by the heterogeneity and anisotropy of geologic rocks and lead to complex behaviors. One of great challenges is to model these coupling processes across the pore scale and continuum scale. The slow development of direct numerical simulation at the pore scale highly limited more fundamental investigations on the coupling mechanisms. Therefore, the present study focuses on the pore-scale imaging and imaging-based numerical approach so that we achieve a more accurate and efficient simulation of the multi-filed coupling behaviors in the realistic geological rocks. In this proposal, the micro-tomographic images of the geological rock, so called digital rock, are reconstructed to capture the detailed geometric structure and composition distribution. An efficient and robust embedded boundary (cut cell) method is presented to describe the complex pore boundary with second order accuracy in cubic Cartesian meshes with local refinement. A new hybrid numerical method is then introduced to model the coupled flow and transport in the complex geological structures, which develops the GPU enhanced Multiple-Relaxation-Time Lattice Boltzmann method for the slipping flow, and the embedded boundary-finite volume-algebraic multigrid method for the heat and mass transfer. Pore-scale modelling of the multi-field coupling problems is then analyzed to deeply understand the physical behaviors, important effects and control mechanisms in some geoscience and environment applications. As a consequence of detailed validations and physical analyses, the work will recommend 1-2 Benchmarks as the modelling reference of the coupled fluid/heat/mass transfer and chemical reactions in the geological rock. Therefore, the work is expected to provide attractive numerical tools and benchmarks to develop the digital rock physics in multi-field coupling problems. This work will expand the scientific knowledge of multi-field coupling mechanisms and then promote more accurate upscaled modelling, prediction and engineering design at the continuum scale.

真实岩心内部的流动-传热传质-反应耦合过程的精细描述，是非常规油气资源开发以及地层二氧化碳封存、环境土壤治理等过程亟待解决以指导工程实践的关键共性科学问题。本项目围绕真实岩心的多物理化学场耦合问题，基于数字岩心技术，通过构建局部加密直角坐标系切削网格剖分方法，建立基于多松弛格子Boltzmann模型与嵌入式边界的有限体积法-代数多重网格模型的混合数值方法，发展一种真实岩心内部多物理化学场耦合过程的孔隙尺度直接数值模拟方法，有望揭示典型案例多孔介质内多场耦合作用的动态现象、演化规律与微观机制，并通过数值模型的细致验证、应用问题的精细建模与数值实验的深入分析，形成1-2个真实岩心多场耦合的直接数值模拟的基准案例。为推动真实岩心的多物理化学场耦合的直接数值模拟提供有效的计算方法与实践路径，为深入认识大尺度宏观物理过程演变规律和非常规油气开发等方案设计与调控提供理论支持。

非常规油气资源勘探开发已成为未来油气的主战场，其开发过程是典型的多物理化学场耦合作用下单相/多相流体在多孔介质内部的热质传递过程。复杂多孔介质流动-传热传质-反应耦合过程的孔隙尺度精细描述，对揭示多场耦合作用的动态现象、演化规律与控制机制尤为关键。本项目结合理论分析、数值基准案例验证与实验结果对照，建立了单相流动-共轭传热-多组分传质-剧烈非均相反应-固相演化的混合尺度微观介质模型，解决了多尺度多孔介质热质传递过程的建模难点；发展了多相流动-共轭传热-跨相传质-非均相反应-固相演化的格子Boltzmann模型，解决了大密度比、多组分多相开放体系非均相反应计算的数值难题；发展了厘米长度的三维数字岩心渗透率的升尺度计算方法，克服了传统渗流模型无法耦合描述流体在裂缝等大尺度非均质结构和基质微孔中多模态流动的计算挑战；开展了单重孔隙介质和基质-裂缝双重介质内部稠油火驱燃烧、天然气水合物降压分解的孔隙尺度数值模拟研究，揭示了多物理化学场耦合作用下火驱燃烧与水合物分解的热质传递特性与控制机制演变机制，形成2个复杂多孔介质多场耦合直接数值模拟的基准案例。本项目为推动多孔介质多物理化学场耦合的直接数值模拟提供有效的计算方法与实践路径。本项目组在国家自然科学基金面上项目的资助下，顺利完成了预定研究任务，发表SCI期刊论文13篇(包括Journal of Fluid Mechanics、Physics of Fluids、Physical Review E/F等数值领域高水平期刊)，EI期刊论文1篇，申请发明专利1项，授权计算机软件著作权4份；培养博士后1人，毕业博士研究生1人，硕士研究生1人。