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为揭示围压及应变速率对页岩力学特性的影响规律,对志留统龙马溪组页岩试样开展了不同围压及不同应变率下的三轴压缩力学试验研究。结果表明,围压和应变率对页岩的弹性模量、峰值强度及破裂形态等均具有显著影响,弹性模量和峰值强度均随围压的升高而增加,峰值强度增加的幅度明显大于弹性模量,峰值强度呈线性增加趋势,低围压时应变率从低到高,弹性模量和峰值强度都呈逐渐升高的趋势,两者与应变率对数的关系可用二次多项式描述;随着围压增大,页岩的应变率效应逐渐减弱,在较高高围压(50 MPa)下峰值强度和弹性模量随应变速率增加而增加现象均变得极不显著。对试验后岩样的破坏模式进行分析可知,页岩在低围压高应变率状态下主要是劈裂–剪切破坏,随着围压的增加和应变率的减小,试样的破坏由脆性劈裂–剪切破坏向单一剪切破坏转变,再逐渐向延性破坏过渡。研究结果对于合理确立页岩力学参数及设计压裂方案具有较好的参考。
In order to reveal the laws of confining pressure and strain rate on the mechanical properties of shale, triaxial compression mechanics tests of the Longmaxi shale samples of the Silurian under different confining pressures and different strain rates were carried out. The results show that the confining pressure and strain rate have significant influence on the elastic modulus, peak strength and rupture morphology of shale. Both the elastic modulus and peak strength increase with the increase of confining pressure, and the amplitude of peak strength increases obviously The elastic modulus and peak intensity show a linear increasing trend. When the confining pressure is low, the strain rate is from low to high, and the elastic modulus and peak intensity are gradually increasing. The relationship between them and the logarithm of strain rate can be described by quadratic polynomial With the increase of confining pressure, the strain rate effect of shale gradually weakened. Under high confining pressure (50 MPa), the peak strength and elastic modulus increased with the increase of strain rate. After analyzing the failure mode of the rock samples, we can see that shale is mainly splitting-shear failure under low confining pressure and high strain rate. With the increase of confining pressure and the decrease of strain rate, the failure of sample Brittle splitting - shear failure to a single shear failure transformation, and then gradually transition to ductile destruction. The results provide a good reference for the reasonable establishment of shale mechanical parameters and design of fracturing scheme.