超临界二氧化碳驱替页岩气动力学及热流固耦合机制

The supercritical carbon dioxide enhanced shale gas recovery is a promising technology with excellent application prospects in china. However, the dynamic of shale gas displacement by carbon dioxide injection, and the coupled mechanism of thermal–hydrologic –mechanical effects during the enhanced shale gas recovery processes, as a very important fundamental issue associated with this technology, requires further investigation. To solve this issue, through the combined methods of experimental study, theoretical analysis and numerical simulation, the following issues such as the thermodynamics and kinetics of shale gas displacement by carbon dioxide, the influence of CO2/CH4 competition adsorption on the deformation behaviour and mechanical characteristics of shale, and the dynamic change of permeability of shale gas reservoir after carbon dioxide injection is going to be investigated in this research. After this study, the single component and multicomponent adsorption models of CO2/CH4 in shale, the adsorption induced deformation model of shale will be established, then the mechanism of CO2/CH4 competition adsorption in shale will be revealed. Subsequently, considering the influence of coupled thermal–hydrologic–mechanical (THM) effects and the CO2/CH4 competition adsorption induced deformation on the permeability, a dynamic permeability model of reservoir during the CO2 enhanced shale gas process will be proposed. Based on the multiphysics processes and the transport mechanism of CO2/CH4 in shale gas reservoir, the multi-field coupled seepage equation of multiphase and multicomponent CO2/CH4 will also be derived. After that, the influence of different factors(stress, temperature, pressure, the injection rate, volum and pattern of CO2) on the shale gas recovery ratio will be obtained. Finally, the principal of carbon dioxide enhanced shale gas recovery and the coupled mechanism of multiphysics processes is analyzed and presented. The results of this research could provide scientific basis and technology support for the engineering application of carbon dioxide enhanced shale gas recovery technology.

超临界CO2强化页岩气开采技术已展示出广阔应用前景，但对于其涉及的多场耦合条件下CO2驱替页岩气动力学及热流固耦合机制等关键科学问题还不清楚。基于此，项目采用实验研究、理论分析、数值模拟相结合的方法，对多场耦合条件下不同相态CO2驱替页岩气热力学与动力学、CO2与CH4竞争吸附作用下页岩变形及力学特性、CO2驱替页岩气动态过程及储层渗透特性动态演化规律开展研究。通过研究，建立不同相态CO2、CH4及其混合流体在页岩中的吸附/解吸、扩散模型，CO2与CH4竞争吸附作用下页岩变形模型，揭示CO2与页岩气竞争吸附机理；建立应力场、温度、孔隙压力与竞争吸附共同作用下储层渗透率动态预测模型、以及多场耦合条件下多组分多相CO2/CH4渗流理论，获得不同因素对CO2驱气效果的影响，揭示CO2驱替页岩气的动力学过程及热流固耦合机制，为超临界CO2强化页岩气开采技术的应用及工程参数的优化提供科学依据。

项目围绕多场耦合条件下不同相态CO2驱替页岩气热力学与动力学、CO2与CH4竞争吸附作用下页岩变形及力学特性、CO2驱替页岩气动态过程及储层渗透特性动态演化规律等关键科学问题，采用实验研究、理论分析、数值模拟相结合的方法，对不同相态CO2-水-页岩相互作用下页岩微观结构及力学特性响应规律、多场耦合作用下CO2、CH4在页岩中的吸附/解吸、扩散规律、多场耦合作用下CO2/CH4在页岩层中的渗流机理开展了系统深入的研究。通过研究，阐明了CO2-水-页岩相互作用对页岩微观结构、矿物组分的影响机理，揭示了储层温度、压力下CO2、CH4竞争吸附的热力学与动力学机理，获得了影响CO2、CH4竞争吸附的主控因素，建立了吸附模型，揭示了超临界CO2提高页岩气采收率机理，CO2的等量吸附热和等量吸附熵均大于CH4，表明CO2与页岩表面的相互作用强于CH4，且页岩中CO2的吸附速率整体上要大于CH4；建立了页岩微观结构变化，CO2、CH4竞争吸附特性及页岩力学性质变化的联系，从微观尺度揭示了CO2-水-页岩相互作用对页岩宏观力学行为的影响机理；获得了T-H-M-C多场耦合作用下页岩渗透特性演化规律，CO2注入页岩后的驱气过程，页岩渗透率受流体注入引起的有效应力变化、CO2、CH4竞争吸附差异性膨胀效应以及CO2-水-页岩相互反应引起的矿物溶解与沉淀效应的共同影响，基于此，建立了渗透率演化模型。研究成果应用于现场试验，为CO2注入压力、注入速率等工程参数优化提供了重要依据，可以为超临界CO2强化页岩气开采及地质封存一体化技术的进一步工程应用提供理论支撑，服务我国碳中和战略目标。