考虑渗流-应力-温度-固相耦合效应的深层页岩气压裂液滤失机理研究

Deep shale gas reservoirs have high in-situ stress and a high difference between two horizontal stresses, which leads to low fracture complexity and low stimulated volume. This greatly restricts the economic and effective development of deep shale gas. Regulating the fracturing fluid leakoff into natural fractures is the key to control the complexity of hydraulic fracture and the stimulated volume. Based on the thermo-poroelastic theory, this project intends to develop a prediction model for the composite stress field on natural fracture face with consideration of matrix leakoff and water-rock heat exchange. In combination with the strength theory of structural weak surface, the activation mode of natural fractures will be determined. Considering the influence of percolation-stress-temperature, the spatio-temporal variation model of natural fracture width will be established for different activation modes. On this basis, considering the plugging effect of injected solid particles, a fracturing fluid leakoff model for natural fractures before and after solid plugging will be established. The laboratory test data and field data will be utilized to verify and improve the models. Then the models can be used to analyze the effects of different factors on fracturing fluid leakoff, including rock mechanical parameters, natural fracture properties, fracturing fluid properties, proppant properties, etc. The research results will enrich and improve the basic theory of complex fracture propagation and provide guidance on the optimal design of volume fracturing in deep shale gas.

深层页岩气储层地应力高、水平两向应力差异大，导致裂缝复杂程度及改造体积低，极大制约了深层页岩气的经济有效开发。调控天然裂缝压裂液滤失是控制深层页岩气裂缝复杂程度和改造体积的关键。本项目拟基于热孔弹性理论，考虑基质孔隙压裂液滤失和水-岩热交换，建立天然裂缝面复合应力场预测模型，结合结构弱面强度理论，判断天然裂缝激活模式；考虑渗流-应力-温度耦合，建立不同激活模式下天然裂缝开度时空演化模型；在此基础上，考虑注入固相颗粒的封堵效应，建立固相封堵前、后的天然裂缝压裂液滤失模型。利用室内实验测试数据和现场数据验证、完善模型，分析岩石力学参数、天然裂缝性质、压裂液性质和支撑剂性质等因素影响压裂液滤失的规律。研究成果将丰富和完善深层页岩气复杂缝网扩展基础理论，为深层页岩气体积压裂优化设计提供依据。

调控天然裂缝压裂液滤失是提高深层页岩气压裂裂缝复杂程度和延伸范围的关键。本项目紧密围绕天然裂缝开启及其压裂液滤失开展研究，考虑基质压裂液滤失、地层温度变化、水力裂缝张开等因素产生的诱导应力，建立了考虑渗流-应力-温度耦合效应的天然裂缝面复合应力场预测模型，揭示了深层页岩压裂过程中压裂液渗滤、地层温度变化和人工裂缝延伸对井周应力场及天然裂缝破坏的影响；考虑综合诱导应力，建立了暂堵前不同破坏模式下天然裂缝压裂液滤失模型；在此基础上，基于Kozeny-Carman公式，考虑固相暂堵剂的粒径分布，建立了暂堵段渗透率预测方程；在此基础上，考虑暂堵后天然裂缝内不同区域，建立了暂堵后天然裂缝内流体压力分布模型；基于不同固相暂堵段失稳模式，结合水力裂缝扩展模型，形成了暂堵后固相暂堵段失稳及天然裂缝压裂液滤失的预测方法，分析揭示了影响天然裂缝压裂液滤失和固相暂堵效果的主控因素。.相关研究成果发表标注本基金SCI收录论文5篇；申请国家发明专利8项，其中已授权4项；参加国际学术会议1次。项目执行期间，项目负责人晋升副教授职称，培养硕、博士7名。研究成果促进了水力压裂基础理论的发展，支撑了四川威荣、湖北红星等地区的深层页岩气压裂优化设计。