页岩三轴压缩条件下的纵横波速特征

Velocity characteristics of P?-wave and S-wave for shale reservoir under tri-axial compression experiments

 程礼军 2 潘林华 2 张烨 2 邓智 2 陆朝晖 2

油气资源与探测国家重点实验室重庆页岩气研究中心，重庆 400042 重庆市页岩气资源与勘查工程技术研究中心（重庆地质矿产研究院），重庆 400042）

 针对页岩层理发育和各向异性强的特点，利用钻井取心进行了一系列三轴压缩条件下的超声波速度测试，获得了不同层理倾角、轴向载荷条件下的纵横波速度变化特性。实验结果表明：1）层理倾角增大，页岩的抗压强度和残余强度呈U型变化趋势，弹性模量逐步增加，泊松比呈先增后减的趋势；2）层理倾角增大，页岩的初始纵横波速度增大；3）随着轴向载荷对页岩内部结构的影响，三轴压缩条件的纵横波速度呈先增后降的趋势；4）页岩水化能增加纵横波速度，大幅度降低页岩的抗压强度；5）页岩动态弹性模量和泊松比的比值与静态弹性模量和泊松比的比值比较接近，相关性较好；6）在围压条件下，页岩弹性模量与泊松比的各向异性系数差别较小。实验结果对于认识和了解页岩的力学、超声波特性，以及声波测井的校正，具有一定指导意义。

 In view of the characteristics of developed bedding and strong anisotropy, a series of ultrasonic velocity experiments were conducted under the tri-axial compression with drilling cores. The variation characteristics of P-wave and S-wave were obtained at different dip angle and axial load. The experimental results show that: when the bedding dip angle increases, the compressive strength and residual strength appear to be U type change tendency with gradually increasing modulus of elasticity while the Poisson′s ratio increases first and then drops; the initial P-wave and S-wave velocities of shale increase with the increase of the bedding dip angle; with the effect of axial load on the internal structure of shale, the velocities of P-wave and S-wave increase first and then decrease; the velocities of P-wave and S-wave increase when the shale hydration occurs; the correlation coefficient of dynamic elastic modulus to static elastic modulus is close to the ratio of dynamic Poisson′s ratio to static Poisson′s ratio, the correlation coefficient are well related; under confining pressure, there are less differences within the anisotropy coefficients of elastic modulus and the Poisson′s ratio of the shale. The experimental results in the article have guiding significance to the understanding and interpretation of mechanical properties, ultrasonic characteristics and acoustic logging.

10.6056/dkyqt201604013