煤层气储层水力裂缝扩展特征与控因研究进展

Research progress on hydraulic fracture characteristics and controlling factors of coalbed methane reservoirs

  • 摘要: 煤层气储层水力压裂后的裂缝展布规律和内部控因在很大程度上决定了储层改造效果,了解水力裂缝特征及扩展机制对煤层气的高效开发具有重要意义,也是水力压裂工艺参数优化的关键理论基础。基于国内外煤层气储层水力压裂开发现状,综合压裂实验设计、理论计算模型和数值模拟等,梳理了不同方法的特征及其差异,并系统论述了煤层气储层内在地质因素和外部工程因素对水力裂缝扩展行为的影响机制,总结了现阶段煤层气储层水力裂缝研究中面临的问题及发展趋势。结果表明:在真三轴物理实验中配置声发射监测和光学成像组件等改进措施可以极大促进水力裂缝扩展的力学行为和延伸路径研究;理论计算模型可以有效量化水力裂缝扩展行为,但预设的裂缝形态和延伸路径会使计算结果偏离实际生产;数值模拟有助于探究储层原位条件下多地质因素控制的水力裂缝网络动态形成过程和多条裂缝之间的相互影响;总体而言,煤层气储层水力裂缝的扩展行为是由天然弱面、地应力、宏观煤岩类型、煤体结构和支撑剂等因素约束下的综合过程。未来研究应聚焦在:① 完善实现水力压裂物理实验中原位温压条件下的裂缝行为实时监控,并形成大尺寸样品制样标准;② 深入研究基本理论计算模型中天然裂缝几何形态及注水速率、压裂液黏度等水力压裂工程参数对水力裂缝交互模式产生的叠加效应;③ 结合现场压裂中的微地震监测数据,优化数值模拟方法中天然裂缝及水力裂缝的几何形态和扩展路径设置;④ 量化多场−多地质因素对水力裂缝网络的耦合作用。

     

    Abstract: The distribution pattern and root causes of fractures resulting from hydraulic fracturing in coalbed methane (CBM) reservoirs significantly affect the effectiveness of reservoir stimulation. A thorough understanding of the characteristics and propagation mechanism of hydraulic fractures is crucial for the efficient development of CBM, and also serves as a fundamental basis for optimizing the parameters of the hydraulic fracturing process. Based on the current situation of CBM reservoirs hydraulic fracturing development both domestically and internationally, this study analyzes the characteristics and differences of various methods for physical experiments, theoretical models, and numerical simulations. Additionally, it systematically reviews the influence mechanism of internal geological factors and external engineering factors on the fracture propagation behavior of CBM reservoir. Also it summarizes the current problems and trends in the hydraulic fracture research. The results show that configuring acoustic emission monitoring and optical imaging components in the true triaxial physical experiment could greatly promote the study on the mechanical behavior and extension path of hydraulic fractures. The theoretical models can effectively quantify the behavior of hydraulic fractures, but the preset fracture shape and extension path of different fractures may cause some deviations from actual production. Numerical simulation can explore the dynamic formation process of the hydraulic fracture network controlled by multiple geological factors under the in-situ condition of reservoir and the interaction among multiple fractures. Furthermore, the hydraulic fracturing of the CBM reservoirs is a comprehensive process constrained by multi-factors such as natural weak plane, in-situ stress, coal macro-lithotype, coal structure, and proppant. Future researches should focus on ① Realizing a real-time monitoring of fracture behavior under in-situ temperature and pressure conditions in the large-scale hydraulic fracturing physical experiments and forming a sample preparation standard; ② Thoroughly studying the superposition effect of natural fracture geometry and hydraulic fracturing engineering parameters (e.g. water injection rate and fracturing fluid viscosity) on the interaction mode of hydraulic fractures in the basic theoretical models; ③ Applying the microseismic monitoring data of field fracturing to optimize the geometric shape and expansion path setting of natural fractures and hydraulic fractures in the numerical simulation; and ④ Quantifying the coupling effect of multi-fields and geological factors on hydraulic fracture networks.

     

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