三轴压缩砂岩水力压裂力学特性试验

Experimental Study on Mechanical Characteristics of Sandstone Under Hydraulic Fracturing by Triaxial Compression

采用RLW-2000M微机控制煤岩流变仪,以砂岩为研究对象,重点分析三轴压缩条件下水压-应变-水压体积曲线演化规律,从水压、应变和水压体积三者关系反映水力压裂过程的力学特征;结合断裂力学观点分析了砂岩的水力压裂裂缝形态及破坏类型.实验结果表明:岩石在水力压裂过程的变形演化规律可分为四个阶段,揭示了孔隙裂隙的注水阶段、弹性变形阶段、体积膨胀阶段和贯通破裂阶段的特征;利用乘幂负指数拟合方程,能较好地模拟ε1-t与P-Vp曲线演化规律且精度较高;孔隙在有效围压剪切、水压挤压张裂和合力的拉伸作用下导致裂缝的发生、发展和贯通.

Mechanical characteristics of sandstone under hydraulic fracturing by triaxial compression tests were investigated by using RLW-2000M coal and rock computer controlled rheological testing machine. Transformation laws of strainpore water pressure curves are the highlight points by triaxial compression. The mechanical characteristics of sandstone under hydraulic fracturing were discussed based on pore water pressure, strain and water volume. The hydraulic fracture morphology and failure type of sandstone were analyzed on basis of fracture mechanics. The results show that the typical deformation evolution involves four stages in hydraulic fracturing process： the pore fissure water injection stage, the elastic deformation stage, the volume expansion stage, and the global rupture stage, and the characteristics of them were revealed. The power of negative exponential is used to fit the ε1 - t and P- Vp curves. The presence of tensile deforma- tion, shear deformation and rupture deformation interaction is accompanied with crack initiation and crack propagation process considering effective confining pressure and pore water pressure.