水力压裂破裂压力计算模型

Calculating models of the breakdown pressure for hydraulic fracturing

水力压裂工艺的关键点是岩石破裂压力的确定。依据破裂模型理论基础的不同,将弹性力学破裂模型和断裂力学破裂模型细分为6类:线弹性拉伸破裂模型、多孔线弹性拉伸破裂模型、特征距离模型、剪切破坏模型、能量释放率模型和应力强度因子模型。在此基础上分析了现有细分模型的基本假设、推导原理、适应性和局限性。结果表明:线弹性拉伸破裂模型、多孔线弹性拉伸破裂模型被普遍应用于矿场设计,但其不能综合考虑升压速率、井眼尺寸等因素对破裂压力的影响;特征距离模型可综合考虑这些因素的影响,但其基于的破裂物理过程假设有待进一步检验;剪切破坏模型基于岩石宏观破坏理论,较适合低弹性模量的高渗砂岩;基于断裂力学理论提出的能量释放率和应力强度因子模型,其物理假设与水力致裂的实际物理过程较为接近,但其在初始裂纹长度等基础参数提取方面存在局限。

The key point of the hydraulic fracturing technology is the determination of the rock breakdown pressure.According to the difference of the theoretical basis of the breakdown model,the elastic mechanics-based model and fracture mechanics-based model can be subdivided into six categories:linear elastic-tensile fracture model,porous linear elastic-tensile fracture model,characteristic distance model,shear failure model,energy release rate model and stress intensity factor model.On this bases,the basic assumptions,deduction principles,adaptability and limitation of the existing subdividing models were analyzed.The results show that the linear elastic-tensile fracture model and porous linear elastic-tensile fracture model are widely used in the field or mine design,but they can not comprehensively consider the influences of the pressure rise rate and borehole sizes and so forth on the fracture pressure;the influences of these factors can be considered comprehensively in the characteristic distance model,but the hypothesis of the fracture physical process based on the model needs to be further tested;the shear failure model is based on the macroscopic failure theory of the rock,which is more suitable for high-permeability sandstone with low elastic modulus;for the presented energy release rate and stress intensity factor models based on the fracture mechanics theory,these physical hypotheses are similar to the actual physical process of the hydraulic cracking,but they have limitations in the extracted basic parameters such as the initial crack length and so on.