中间主应力与层理方向对页岩力学和渗透特性影响的试验研究

 为探讨中间主应力与层理方向对页岩力学和渗透特性的影响，运用自主研制的多功能真三轴流固耦合试验系统，以含气页岩为研究对象，进行真三轴应力条件下不同中间主应力加卸载试验。研究结果表明：中间主应力对页岩渗透率的影响在中间主应力垂直于层理面时最大，最小主应力垂直于层理面时次之，最大主应力垂直于层理面时最小；当中间主应力垂直于层理面或平行于层理面时，中间主应力与渗透率呈负相关。中间主应力垂直于层理面时渗透率对中间主应力的敏感性明显大于中间主应力平行于层理面时的敏感性，二者相差1～2个数量级；此外，定义损伤变量D表达式，发现加载过程中损伤变量–中间主应力曲线斜率变化不大，而在卸载过程中斜率变化明显，中间主应力垂直于层理面时损伤变量全程大于中间主应力平行于层理面时的损伤变量。

Experimental study on the effect of intermediate principal stress and bedding direction on mechanical properties and permeability of shale

The loading-unloading tests to gas-bearing shale under the true triaxial stress conditions with different intermediate principal stresses were carried out with the multifunctional true triaxial test system developed in house for fluid-solid coupling to explore the influence of intermediate principal stress and bedding direction on mechanical properties and permeability characteristics of shale. The results indicate that the effect of intermediate principal stress on the permeability of shale is greatest when the intermediate principal stress is perpendicular to the bedding plane，is lower when the minor principal stress is perpendicular to the bedding plane，and is lowest when the maximum principal stress is perpendicular to the bedding plane. When the intermediate principal stress is perpendicular to the bedding plane or parallel to the bedding plane，the intermediate principal stress is negatively correlated with the permeability. The permeability is more sensitive to the intermediate principal stress when the intermediate principal stress is perpendicular to the bedding plane than parallel to the bedding plane (the difference is 1 or 2 orders of magnitude). In addition，the expression of the damage variable D was defined. The slope of the damage variable-intermediate principal stress curve changes little during the loading process and changes obviously during the unloading process. The damage variable is bigger when the intermediate principal stress is perpendicular to the bedding plane than parallel to the bedding plane during the whole process.