多场耦合作用下页岩气储层网络裂缝宏-细观演变机理及压裂参数优化研究

This project is international frontier research in the field of rock mechanics. It aims to improving the flow conductivity of the shale-gas network crack in China's new green and low-carbon energy exploitation, by studying macro-micro evolution mechanism of the shale-gas network cracks and parameter optimization of the hydraulic fracturing technology under multi-field coupling conditions. Firstly, hydraulic-mechanical-chemical coupling fracture theory (including crack initiation criterion, crack propagation control equation, crack coalescence condition and fracture criterion) and mesoscopic fracture criterion of the arbitrary multi-cracks (including arbitrary length and inclination angle) are established based on fracture mechanics, damage mechanism, fluid mechanics and chemical kinetics. And then, a new characterization method of network crack flow conductivity is proposed and new test methods of multi-crack propagation length real-time monitoring and network crack conductivity characterization parameters are proposed under multi-field coupling conditions. Fracture tests of shale multi-cracks and their numerical simulation are conducted in order to reveal the macro-micro evolution mechanism and influencing factors of the shale-gas network cracks. Finally, the optimal hydraulic fracturing technology parameters are determined for increasing the flow conductivity of the shale gas network cracks. This study is of great significance not only for the development of rock fracture mechanics, but also for the improvement of hydraulic fracturing technology and shale-gas exploitation efficiency.

本项目瞄准国际岩石力学领域研究前沿，针对我国新型清洁低碳能源——页岩气开发工程中亟待解决的提升页岩气储层网络裂缝导流能力关键问题，开展多场耦合作用下页岩气储层网络裂缝宏-细观演变机理及压裂参数优化研究。在断裂力学、损伤力学、流体力学、化学动力学相结合的理论框架下，建立多场（渗流场、应力场、化学场）耦合作用下任意多裂纹（含任意长度、方位角）扩展理论（含起裂判据、裂纹扩展控制方程、贯通条件、断裂准则等）以及颗粒流细观断裂准则，提出网络裂缝导流能力表征方法，研制多裂纹扩展长度实时监测方法和网络裂缝导流能力表征参数测试方法；通过多场耦合作用下多裂纹断裂试验及数值模拟，揭示页岩气储层网络裂缝宏-细观演变机理及网络裂缝导流能力的影响因素规律，提出多场耦合作用下页岩气储层水力压裂参数优化方案。研究结果不仅对岩石断裂力学发展具有重要的理论意义，而且对我国页岩气压裂技术改进和高效开发具有重要的应用价值。

本项目瞄准国际岩石力学领域研究前沿，针对我国新型清洁低碳能源——页岩气开发工程中亟待解决的提升页岩气储层网络裂缝导流能力关键问题，开展了水-力耦合作用下页岩气储层网络裂缝宏-细观演变机理及压裂参数优化研究。在断裂力学、渗流力学、各向异性弹性力学相结合的理论框架下，建立了在渗流场和应力场耦合作用下各向同性和正交各向异性岩石任意多裂纹（含任意长度、方位角）断裂理论（含起裂判据、扩展准则等）；基于球面对称设计法和中心组合设计法，提出了颗粒流（PFC）离散元模型的细观参数定量确定方法, 并建立了基于局部拉-剪裂纹数之比的多场耦合作用下多裂纹PFC细观断裂准则；根据多裂纹扩展长度预测理论，提出了岩层网络裂缝导流能力表征方法；通过开展各向同性和正交各向异性岩石多裂纹（含交叉裂纹）水-力耦合断裂和水压致裂试验以及PFC数值模拟，揭示了多裂纹扩展贯通而形成网络裂缝的宏-细观机理及其影响因素规律，提出了页岩气储层水力压裂参数优化方案，并验证了所建立的各向同性和正交各向异性岩石多裂纹水-力耦合宏观断裂理论以及细观断裂准则的有效性。研究结果不仅对岩石断裂力学发展具有重要的理论意义，而且对我国页岩气压裂技术改进和高效开发具有重要的应用价值。