我国页岩气储量居世界首位，页岩气开发正在成为维护我国能源安全与促进供给革命的重要手段。页岩气通常需要采用水力压裂来开采，水力压裂液只有一小部分返回到地表，残余的压裂液会对地下环境构成潜在威胁。目前对压裂液及压裂污染物在页岩气储层内迁移行为的研究尚不充分，制约着页岩气的科学有效开采与环境污染控制。为增进对页岩气地层内压裂液两相渗流、压裂污染物长期迁移扩散的科学认识，论文基于非平衡热力学与混合耦合理论建立了新的页岩气地层双孔隙介质热-两相渗流-力学-化学场多场耦合理论模型，采用COMSOL求解耦合方程组，以实际页岩气井放喷期压裂液返排与生产期残余污染物迁移为应用案例，进行了模拟预测。论文取得的主要研究成果包括：

（1）基于非平衡热力学与混合耦合理论推导建立了页岩气双孔隙介质内两相渗流-力学耦合理论模型（HGM）。分别从两相流体混合物和分离流体相角度，探究了两相渗流与岩石变形耦合理论框架，并通过前人试验数据与理论模型进行了验证。分析结果表明平均流体假设可以在不引入过多参数的前提下捕捉毛细效应，为研究吸附性双孔隙介质中热-渗流-力学-化学耦合行为提供了基础。

（2）在两相渗流与岩石变形耦合理论框架下，基于非平衡热力学和混合耦合理论推导建立了新的页岩地层吸附性双孔隙介质内热-两相渗流-力学-化学场多场耦合理论模型（THGMC-sorp）。模型获取了吸附性双孔隙介质内热-两相渗流-力学-化学场耦合本构关系、扩展的达西定律、菲克定律、傅里叶定律，通过引入吸附熵产确定了分子吸附对固体变形的影响。模型通过现有的一维热固结问题THM耦合解析解得到了验证。该模型提出了新的孔隙、裂隙孔隙度变化方程，以及热、两相渗流、力学、化学场耦合控制方程，从理论上确定了吸附性双孔隙介质内多场耦合效应对污染物迁移的影响，为模拟页岩气储层内压裂污染物热-两相渗流-力学-化学场耦合迁移提供了理论工具。

（3）采用COMSOL软件求解吸附性双孔隙介质两相渗流-力学耦合控制方程组（HGM-sorp），建立实际页岩气生产井压裂液返排两相流数值模型，通过气-水两相流速监测数据对模型进行了验证。基于验证的模型模拟研究了返排期间页岩气地层两相渗流-力学耦合行为，预测了压裂液返排速率及累计返排量，确定了气体吸附耦合效应对压裂液返排预测的影响。模拟结果表明超过94%的注入压裂液在放喷返排阶段后仍残余在地层中，可能存在长期的环境风险。

（4）选取乙二醇丁醚（2-Butoxy ethanol）作为模拟特征污染物，采用COMSOL软件求解吸附性双孔隙介质热-两相渗流-力学-化学场耦合控制方程组（THGMC-sorp），建立了实际场地返排后地层内残余压裂污染物多场耦合迁移数值模型。通过模拟确定了返排后页岩气地层内热-渗流-力学-化学场耦合演化行为并分析了不同耦合效应对污染物迁移的影响。模拟结果表明储层裂隙内污染物最大扩散高度为26m，生产15年后累计排出污染物占注入污染物总量的20.77%。残余污染物逐渐从溶解态向吸附态转移，吸附态污染物15年后最终占比达到3.28%。

China's shale gas reserves rank first in the world. Shale gas development is becoming an important means to maintain China's energy security and promote the energy supply revolution. Shale gas exploitation usually requires the use of hydraulic fracturing technology, while only a small part of the fracturing fluid can be returned to the surface. The residual fracturing fluid pose a potential threat to the subsurface environment. The research of transport behavior of fracturing fluid and contaminants is insufficient, which constrain the scientific and effective exploitation of shale gas and the control of environmental pollution. In order to promote the scientific understanding of two-phase flow of fracturing fluids and long-term transport of fracturing pollutants, this thesis, build a novel thermo-hydro-gas-mechanical-chemical coupled theoretical model in dual-porosity media of shale gas formation, based on the non-equilibrium thermodynamics and mixture-coupling theory. Numerical modeling and prediction are carried out based on COMSOL, using the fracturing fluid flow-back during flow-back stage, and residual contaminant transport during production stage of a real site as the applied cases. The main research results achieved in the thesis include:

(1) Based on the non-equilibrium thermodynamics and mixture-coupling theory, a coupled hydro-gas-mechanical theoretical model (HGM) was established in the dual-porosity media of shale. The theoretical framework of the coupled two-phase flow and rock deformation is explored from the viewpoints of considering the two-phase fluids as a mixture (average fluid) or as separated fluid phases, respectively, and the model is validated by the experimental data and theoretical models of the previous researchers. The analysis shows that the average fluid assumption can capture capillary effects without introducing excessive parameters. The model provides a basis for studying the coupled thermo-hydro-gas-mechanical-chemical behavior in sorptive dual-porosity media.

(2) Using the theoretical framework of two-phase flow coupled with rock deformation, a novel theoretical model of thermo-hydro-gas-mechanical-chemical model in sorptive dual-porosity media (THGMC-sorp) in shale formations is established based on the non-equilibrium thermodynamics and mixture-coupling theory. The model determines the coupled thermo-hydro-gas-mechanical-chemical constitutive relationship, extended Darcy's law, Fick's law, and Fourier's law in sorptive dual-porosity media, and determines the effect of molecular sorption on the solid deformation by introducing sorption entropy production. The model is verified by an existing analytical THM coupled solution of the 1D thermal consolidation problem. The model proposes new equations for the evolution of pore and fracture porosity, as well as coupled governing equations for thermo, two-phase flow, mechanical, and chemical fields, which theoretically determines the influence of multi-field coupling effects on contaminant transport within sorptive dual-porosity media, and provides theoretical tool for modeling the coupled thermo-hydro-gas-mechanical-chemical field transport of fracturing contaminants within shale gas reservoirs.

(3) The hydro-gas-mechanical governing equations for sorptive dual-porosity media (HGM-sorp) is solved by COMSOL software, and a numerical model of two-phase flow of fracturing fluid in real shale gas wells is established, which is validated by the site-monitored gas-water flow rate data, the validated model is used to study the hydro-gas-mechanical coupling behaviors of the shale gas formation during the flow-back stage, and to predict the rate and cumulative volume of the flow-back fluid. The hydro-gas-mechanical coupling behavior in the shale gas formation during the flow-back stage was investigated, the fracturing fluid flowback rate and the cumulative flowback volume were predicted, and the effect of gas sorption on the prediction of the fracturing fluid flow-back was determined. The simulation results showed that more than 94% of the injected fracturing fluid was left in the reservoir after the flow-back stage, which may have long-term environmental risks.

(4) 2-Butoxy ethanol was selected as the characteristic pollutant for simulation, and the COMSOL software was used to solve the coupled governing equations of thermo, two-phase flow, mechanical and chemical fields of the sorptive dual-porosity media (THGMC-sorp), so as to establish a numerical model for the multi-field transport of residual fracturing pollutant in the reservoir after flow-back stage. After simulation, the evolution of the coupled thermo-hydro-gas-mechanical-chemical behaviour in the shale gas formation after flow-back was determined, and the influence of different coupling effects on the transport of pollutants was analyzed. The simulation results show that the maximum diffusion height of the pollutants in the reservoir fractures is 26 m, and the cumulative pollutants discharged after 15 years of production account for 20.77% of the total pollutants injected. The residual pollutants gradually transferred from dissolved phase to adsorped phase, and the final percentage of adsorped pollutants reached 3.28% after 15 years.