深层页岩水力裂缝闭合的蠕变机理研究

Shale is strongly characterized with creepage subjected to high in-situ stress state. With the development of deep shale reservoirs under 3500 meters, the increasing requirement for studying the long term availability of hydraulic fractures in shale arises from the low production and fast degradation after fracturing construction. Faced with the difficulties for uncovering the scientific mechanisms of deformation and closing of hydraulic fractures in shale, this project focuses on the following research items to find theoretical and technological solutions for achieving long-term high production after hydraulic fracturing: 1) conducting creepage experiments for fractured fluid-saturated shale rock with supporting proppants involved within to research on the effects of temperature, stress, pore fluid and proppant on the creepage mechanism of shale rocks and further construct corresponding constitutive equations to represent the creeping process with the coupling of mechanics and chemistry under complicated conditions; 2) constructing an advanced model with the effect of dynamic creeping process to disclose the gas transport mechanism in the coupling matrix-fracture system so as to obtain the long term evolution of the fracture conductivity, subsequently investigating the degenerative behavior of the fracture productivity. The ultimate goal of this project is to build the fundamental theories for fracturing and subsequent exploitation for shale reservoirs and in turns to provide experiences and theoretical guides for exploiting other similar gas reservoirs.

页岩在高应力条件下具有明显的蠕变特征。随着3500米以深的深层页岩气的规模开发，压裂后产量低、递减速度快呈显著特征，急需探究深层页岩水力裂缝的长期有效性问题。围绕深层页岩水力裂缝蠕变闭合机理的关键科学问题，开展含裂缝、流体与支撑剂的页岩蠕变实验，探索温度、应力、裂缝、流体及支撑剂影响下页岩蠕变规律，建立力学与化学耦合的页岩蠕变本构方程，揭示其蠕变机制；研究页岩蠕变和基质与裂缝间流动耦合的气体流动特征，建立页岩水力裂缝导流能力的蠕变模型，分析长期生产中深层页岩水力裂缝导流能力的递减规律，揭示页岩水力裂缝闭合的蠕变机理，为深层页岩气压裂与开发设计提供科学依据,同时也为类似气藏开采的基础研究提供实验方法和理论借鉴。

页岩在高应力条件下具有明显的蠕变特征。随着3500米以深的深层页岩气的规模开发，水力压裂后产量低、递减速度快呈显著特征，急需探究深层页岩水力裂缝的长期有效性问题。针对上述难题，本项目围绕深层页岩水力裂缝蠕变闭合机理的关键科学，运用岩石力学、断裂力学、实验力学和渗流力学的理论方法开展一系列研究，主要取得了以下成果与认识：（1）借助高温高压岩石流变仪，研制了复杂应力下页岩水力裂缝蠕变与长效导流能力评价装置，发现了页岩蠕变的各向异性特征；采用微纳米表征方法，发现了平行层理面和垂直层理面裂缝水化损伤的差异性，揭示了页岩水力裂缝蠕变各向异性的微观作用机制。（2）发现了页岩基质与裂缝界面在深度赋存温度、压力和化学流体环境下微观结构损伤特征，建立了页岩水力裂缝导流能力的蠕变模型，发现了页岩Ⅰ和Ⅱ缝导流能力的差异性；提出了基于卷积神经网络的页岩水力裂缝壁面力学特征方法，定量表征了页岩水力裂缝壁面在储层流体耦合作用力学特征演化规律，揭示了深层页岩水力裂缝在蠕变、渗流和温度耦合下导流能力的递减机制。（3）基于上述模型，建立深层页岩水力裂缝与天然裂缝导流能力与产能的计算模型，分析了生产过程页岩裂缝系统变形对流动特征与产量规律，中岩石变形对气体流动的影响规律，为深层页岩气压裂与开发设计提供了科学依据，同时也为类似气藏开采的基础研究提供了实验方法和理论借鉴。.相关研究成果在《Rock Mechanics and Rock Engineering》和《中国科学：物理学 力学 天文学》等国内外行业高水平期刊发表论文14篇，其中SCI、EI论文10篇，北大中文核心4篇，授权发明专利2项，获得省部级科技进步二等奖1项。