天然气水合物资源在全球分布广泛、储量丰富，是具有前景的清洁能源。然而目前天然气水合物开采仍面临生产效率低下等技术难题，至今未能实现大规模商业开发。由于天然气水合物分解是多孔介质中复杂的多物理化学问题，从孔隙尺度出发，认识水合物分解控制机制，对指导水合物高效开采具有重要意义。本研究针对天然气水合物分解过程，开展了孔隙尺度研究，分析了水合物分解过程多物理化学场控制机制，推动了水合物分解过程的尺度升级研究，为实现天然气水合物高效开发提供了理论基础。本研究基于格子Boltzmann（LB）方法，构建了耦合多相流动、跨相传质、共轭传热、非均相反应、固相演化的孔隙尺度数值模型，用于模拟封闭多孔介质结构中天然气水合物分解所涉及的多物理化学场耦合问题。针对开放体系中甲烷的跨相传质问题，提出了耦合连续组分输运（CST）模型的LB方法，即CST-LB模型。针对CST-LB模型，提出了非均相化学反应边界条件处理格式，针对多组分伪势LB模型，提出了改进的局部平均虚拟密度润湿边界处理格式，实现了开放体系天然气水合物多场耦合问题的数值模型的构建。利用构建的多场耦合数值模型，本研究针对天然气水合物分解控制机制的认识开展了孔隙尺度数值研究。通过方腔水合物降压分解过程的数值计算，认识了传热传质的影响机制；通过数值模拟与实验结果的对比，确定了水合物分解实际控制机制为扩散控制，指出了传质限制作用是影响天然气水合物分解速率的主导因素；通过模拟多孔介质储层中注N2驱替法分解水合物的过程，研究了气水运移规律对水合物分解过程的影响，明确了不同气水运移条件下的水合物分解模式，量化了不同分解模式下传热传质的限制作用与竞争关系，获得了天然气水合物分解模式相图。这些控制机制研究为天然气水合物开采方案的改进提供了理论基础。基于对水合物分解过程控制机制的认识，本研究提出了基于有效水层厚度的修正反应动力学模型，使表征单元体积（REV）尺度动力学模型的修正具有更明确的物理意义；基于不同水合物分解模式固相结构演化规律，获得了渗流模型、水合物表面积模型等参数，说明了渗流模型应根据水合物分解模式进行选取。这些尺度升级研究推动了天然气水合物生产预测准确性的提高。

Methane hydrate is widely distributed in the world with abundant reserves, which is regarded as the promising clean energy resource. However, the methane hydrate exploitation still faces numerous technical difficulties and the commercial development has not been achieved. Since the methane hydrate dissociation involves complicated multiple physicochemical mechanisms within the porous media, pore-scale understanding of the controlling mechanisms is significant to improve the production practice. The present work carried out the pore-scale numerical investigation on the methane hydrate dissociation process. The multiple physicochemical mechanisms were analyzed and the upscaling work for the production forecast was conducted, which aimed to provide a theoretical basis for the high-efficiency development of methane hydrate reservoir.In the present work, the numerical model based on lattice Boltzmann method was proposed by coupling the multiphase fluid flow, interfacial mass transport, conjugate heat transport, heterogeneous chemical reaction and solid structure evolution. This model can simulate methane hydrate dissociation process in the closed porous structure. To simulate interfacial mass transport in the open system, the continuum species transport-lattice Boltzmann (CST-LB) model was proposed. Moreover, the boundary scheme of the heterogeneous chemical reaction was derived for the CST-LB model, and an improved wetting boundary scheme named the local-average virtual density scheme was proposed for the multicomponent pseudopotential model. By involving the CST-LB model with suitable boundary schemes, the numerical simulation of methane hydrate dissociation in the open system can be realized.Using the proposed numerical models, pore-scale numerical study was conducted on the methane hydrate dissociation process. By computing the depressurization dissociation process of methane hydrate in the square cavity, the role of mass-transport-limitation and heat-transport-limitation was identified. Hereafter, the actual controlling mechanism of the methane hydrate dissociation was determined by comparing the numerical and experimental results. The mass-transport-limitation proved to be the dominant factor affecting the methane hydrate dissociation rate. Methane hydrate dissociation in the porous media with N2 flooding was simulated to understand the effect of gas-water migration on the dissociation process. The methane hydrate dissociation patterns under different fluid flow conditions were classified and the limitation effect and competition relationship of heat and mass transport was quantified. According to the analyses of the dissociation patterns and controlling mechanisms, the regime diagram of the methane hydrate dissociation patterns was obtained. These numerical works on the controlling mechanisms provided the theoretical basis for the improvement of methane hydrate development technique.Based on the understanding of the controlling mechanisms, a modified dissociation kinetic model was proposed with the equivalent water layer thickness for the representative element volume (REV) scale modelling. Moreover, the permeability model and hydrate surface area model were computed with the solid structure evolution scheme of different dissociation patterns. The results proved that the permeability model should consider the dissociation mechanisms. These upscaling investigations help to improve the accuracy of the methane hydrate production forecast.