考虑固体变形与多重流动机制的页岩气运移数值模拟

发布时间：2018-03-28 03:14

本文选题：页岩气运移　切入点：表面吸附扩散　出处：《西南科技大学》2017年硕士论文

【摘要】：页岩气在页岩微纳米孔隙和裂缝系统中的流动是一个多物理场耦合的复杂过程。准确理解页岩气在页岩中的运移对页岩气的高效开采有着重要的意义。本文考虑页岩固体变形和包括黏性流、Knudsen扩散和表面吸附扩散的多重流动机制,利用COMSOL Multiphysics软件对页岩气的运移进行了数值模拟和参数分析。重点关注页岩变形情况下,表面吸附扩散和页岩储层特性参数对页岩气流动能力的影响。本文的主要工作包括:(1)基于各向同性弹性孔隙介质的Biot理论,考虑固体变形和多重流动机制的耦合,即应力-渗流耦合,分别建立了页岩储层单孔介质模型和双孔介质模型的流固耦合方程。包括页岩储层变形平衡方程、页岩气体流动控制方程、孔隙度演化方程和视渗透率方程。(2)基于页岩储层单孔介质模型,对单轴应变和应力约束条件下的页岩气运移进行了数值模拟,定量分析了表面吸附扩散和页岩储层参数对表征页岩气流动能力的固有渗透率、视渗透率和Knudsen数的影响。研究发现:页岩气的运移取决于孔隙压力、解吸附、Knudsen扩散和表面吸附扩散等因素相互竞争的结果。表面吸附扩散与Knudsen扩散是相互独立的两种流动机制,是决定页岩气流动能力的两个关键因素。尤其随着压力的降低,表面吸附扩散的影响更加明显,忽略该影响将给出更低的视渗透率,即更弱的气体流动能力。相比表面吸附扩散和Knudsen扩散,页岩变形对渗透率和Knudsen数的影响很小。其中,影响页岩气流动Knudsen数的参数包括页岩初始孔隙率、页岩初始渗透率、孔隙体积模量和页岩边界压力;对视渗透率有较大影响的参数有页岩初始孔隙率、页岩初始渗透率、页岩初始杨氏模量、孔隙体积模量、Langmuir压力常数、Langmuir体积应变、页岩边界压力和约束应力;而对固有渗透率产生较明显影响的参数则包括页岩初始杨氏模量、页岩颗粒体积模量、孔隙体积模量、Langmuir压力常数、Langmuir体积应变、孔隙吸附应变与页岩吸附应变比值、页岩边界压力和约束应力。此外,在应力约束条件下,页岩气流动能力通常比单轴应变条件下稍弱,各参数对页岩气流动能力的影响与单轴应变条件下相似。(3)基于页岩储层双孔介质模型,对单轴应变条件下的页岩气运移进行了数值模拟和参数分析。研究表明:当存在天然裂缝时,基质孔隙中的页岩气流动明显加快,但对于给定的孔隙压力,页岩气在基质孔隙中的流动能力几乎没有改善。由于裂缝系统的高渗透率,裂缝系统的表面吸附扩散对基质孔隙中页岩气流动能力和流动速率的影响可以忽略。裂缝系统对基质孔隙系统流动能力的影响主要通过改变页岩的固体变形来实现,主要的影响参数有裂缝系统的Langmuir压力常数、Langmuir体积应变以及裂缝系统的杨氏模量。
[Abstract]:The flow of shale gas in shale micropore and fracture system is a complicated process of multi-physical field coupling. It is important to understand accurately the migration of shale gas in shale gas production. Shale solid deformation and multiple flow mechanisms including viscous flow Knudsen diffusion and surface adsorption diffusion, The numerical simulation and parameter analysis of shale gas migration are carried out by using COMSOL Multiphysics software. The influence of surface adsorption diffusion and shale reservoir characteristic parameters on shale gas flow capacity. The main work of this paper includes: 1) based on the Biot theory of isotropic elastic porous media, the coupling of solid deformation and multi-flow mechanism is considered. That is, stress-percolation coupling, the fluid-solid coupling equations of single pore medium model and two-pore medium model of shale reservoir are established respectively, including shale reservoir deformation equilibrium equation, shale gas flow control equation. Based on the single pore medium model of shale reservoir, the migration of shale gas under uniaxial strain and stress constraints is numerically simulated. The effects of surface adsorption diffusion and shale reservoir parameters on the intrinsic permeability, apparent permeability and Knudsen number of shale gas flow are quantitatively analyzed. It is found that the migration of shale gas depends on pore pressure. Desorption Knudsen diffusion and surface adsorption diffusion are competing results. Surface adsorption diffusion and Knudsen diffusion are two independent flow mechanisms and two key factors determining shale gas flow capacity, especially with the decrease of pressure. The effect of surface adsorption diffusion is more obvious. Ignoring this effect will result in lower apparent permeability, that is, weaker gas flow capacity. Compared with surface adsorption diffusion and Knudsen diffusion, shale deformation has little effect on permeability and Knudsen number. The parameters affecting Knudsen number of shale gas flow include shale initial porosity, shale initial permeability, pore volume modulus and shale boundary pressure. The initial Young's modulus of shale, pore volume modulus and Langmuir pressure constant of Langmuir volume strain, shale boundary pressure and confining stress, and the parameters that have obvious influence on the inherent permeability include the initial Young's modulus of shale, the volume modulus of shale particle, the volume modulus of shale particle. The pore volume modulus of Langmuir pressure constant is Langmuir volume strain, the ratio of pore adsorption strain to shale adsorption strain, shale boundary pressure and confined stress. In addition, the flow capacity of shale gas is usually slightly weaker than that under uniaxial strain. The influence of each parameter on shale gas flow capacity is similar to that under uniaxial strain condition. The numerical simulation and parameter analysis of shale gas migration under uniaxial strain conditions are carried out. The results show that the shale gas flow in matrix pores accelerates obviously when there are natural fractures, but for a given pore pressure, The flow capacity of shale gas in matrix pores has hardly improved. Due to the high permeability of fracture system, The influence of surface adsorption diffusion of fracture system on shale gas flow capacity and flow rate in matrix pores can be neglected. The effect of fracture system on the flow capacity of matrix pore system is mainly realized by changing the solid deformation of shale. The main influencing parameters are the Langmuir pressure constant and the Young's modulus of the fracture system.
【学位授予单位】：西南科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE31

【相似文献】