流体黏性对油井砂岩力学响应的影响

随着黏度较大的油藏陆续投入开发，油藏黏性对储层砂岩力学特性的影响研究意义重大。基于柱坐标系建立射孔试验的三维颗粒流数值模型，考虑不同黏性的流体运动对砂岩力学响应的影响，反映油井的出砂过程。砂岩的宏观应力曲线说明流速相同时，随着黏滞系数的增大，切向应力和偏应力均增大，使得砂岩剪切破坏的几率增大，砂岩更容易屈服破坏而出砂。另外，砂岩黏结应力图说明油井附近的应力较大，且随着黏滞系数增大，黏结张拉应力的增大是局部的，而剪应力的增大是全局的，且变化趋势更明显；颗粒的旋转也说明随着流体黏性的增大，颗粒旋转增大，砂岩形成离散颗粒而出砂的几率增大。上述结果与实际开采中的砂岩力学响应吻合，说明了在相同的外界条件下，黏性越大的流体运动对砂岩受力的影响越大，出砂越明显，该成果对不同黏性的油藏开采采用有效的防砂方法提供了重要的科学依据。

Influence of fluid viscosity on mechanical response of sandstone around oil wellbore

Oil viscosity affecting the mechanical characteristics of sandstone around the oil wellbore plays a significant role on oil extraction with the more viscous oil reservoir development. Based on cylindrical coordinate system, a numerical model using 3-dimensional particle flow code (PFC3D) of the perforation test is forward to simulate the oil extraction. For the numerical model, different viscous fluids are considered to simulate the mechanical response to practically reflect the process of the sand production. The macro stress curves indicate that under the same fluid flowing, the increasing fluid viscosity increases the tangential stress and deviatoric stress of the sand, and it also increases the shear failure probability so as to make the sand yielded more easily and have more sand production. And also, bond stress indicates that the largest stress is close to the inner oil, and the increasing fluid viscosity increases the tensile stress as localization and also increases the shear stress as globalization with obvious variation trend; the particle rotation also indicates that the increasing viscosity makes the particle rotated more strongly, and increases the probability of the dislodged particles from the sand to become the sand production. The above results agree with the practical response of the sand during oil extracting, and indicate that under the same conditions, more viscous fluid has greater influence on the mechanical response of the sand and has more obvious sand production. Therefore, the achievement will provide an important base for using effective sand control methods for different viscous oils.