Influences of anisotropic mechanical properties in the hydraulic fracturing design in shale reservoirs
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摘要: 岩石力学性质及地应力等地质力学参数是进行储层压裂改造的基础数据，影响着整个压裂设计的准确性。由于页岩层理发育及矿物组成的复杂性、页岩力学性质的横观各向同性，所以基于传统力学模型获取的压裂参数设计将丧失意义。以横向各向同性模型体现层理发育页岩储层的力学性质，通过简化的横纵弹性模量和泊松比可以较好地表达出页岩的横观各向同性，并总结了横观各向同性地应力解释方法。基于上述理论，应用商业化水力压裂数模软件对四川盆地某层理页岩储层进行了压裂设计，比较横观各向同性模型与传统模型解释力学参数差异，非常规储层动静态力学参数转换，同时通过改变射孔位置研究了起裂点对裂缝形态的影响。研究发现，横观各向同性解释的杨氏模量、地应力要略高于传统方法，同时横观各向同性解释的地层地应力差较小，所以受不同射孔位置的变化对裂缝几何的形态影响要远远高于各向同性模型模拟的结果，特别是缝高变化更为明显。同时数据表明，在高应力区射孔将形成更为狭窄缝宽的水力裂缝，这会严重影响后续支撑剂的进入，以上结论将为提高页岩储层的压裂设计精确性给予重要帮助。Abstract: Rock properties and in-situ stress can provide basic information for stimulated reservoir volume， and they affect fracture propagation evidently. Since shale has well developed lamination， the conventional methods with sonic velocity data， without considering special shale anisotropy， always express apparent error. A transverse isotropic model was presented to illustrate the unique rock properties of shale and a novel stress calculation method was investigated. The differences in rock mechanical parameters between isotropic model and anisotropic model were analyzed， and conversion of dynamic and static mechanical parameters was also presented. It was found the young’s modulus and the stress were greater than those from the conventional methods. The influence of initiation pressure from the anisotropic model was more obvious than that from the isotropic model. Fracturing simulation was performed with fracturing optimization software for shale formation in Jiaoshiba， Fuling. Numerical results show the fracture width is impacted noticeably and the anisotropy model underestimates the fracture height growth， which can provide technology support for in-situ fracturing treatment.
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Key words:
- shale reservoir /
- anisotropy /
- mechanical parameter /
- fracture /
- hydraulic fracturing
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