高温下页岩三轴压缩实验及井壁稳定研究

通过高温下页岩的三轴压缩实验,结合井壁稳定分析理论,进行了高温下页岩的力学特性及井壁稳定性研究。结果表明:高温引起页岩强度劣化,在温度低于150 ℃时,温度对页岩强度劣化主要体现在粘聚力弱化,在温度超过150 ℃时,温度会进一步导致页岩内摩擦角减小。钻井液与地层间的温差将在井周附加热应力,随着远离井壁,温差附加径向热应力先增加后降低,在距离井壁一定位置出现最大值,而附加的切向热应力在井壁处最大。随着温差增加,井壁坍塌压力增加,并且附加热应力引起的坍塌压力增幅逐渐超过页岩粘聚力弱化引起的坍塌压力增幅。研究结果对于钻井施工,优化钻井液设计具有重要的意义。

Triaxial Compression Experiment and Wellbore Stability Study of Shale under High Temperature

Through the triaxial compression experiments of shale under high temperature and the theory of wellbore stability analysis, the mechanical properties of shale and the stability of borehole under high temperature are studied. The results show that the high temperature causes the shale strength to deteriorate. When the temperature is lower than 150 ℃, the shale strength degraded by temperature is mainly reflected in the weakening of the cohesive strength. When the temperature exceeds 150 ℃, the temperature will further reduce the friction angle of shale. The temperature difference between the drilling fluid and the formation will add thermal stress to the well. The radial thermal stress increases first and then decreases with the distance increasing from the well wall, and the maximum value appears at a certain distance from the well wall, and the largest additional tangential thermal stress occurs at the well wall. As the temperature difference increases, the collapse pressure of the well wall increases, and the collapse pressure increase caused by the additional thermal stress gradually beyond the collapse pressure increase caused by the weakening of the shale cohesion. The research results are of great significance for drilling construction and optimizing drilling fluid design.