考虑流固耦合效应的储层砂岩力学响应分析

用柱坐标系下的三维颗粒流数值方法研究储层砂岩的力学响应。通过实际颗粒级配的数值模拟与室内三轴试验对比,确定砂岩颗粒的细观力学参数,建立基于流固耦合效应的射孔试验模型。结果表明:砂岩的宏观应力反映了油藏流速对砂岩应力的增幅,但均未超过储层砂岩的峰值强度,最大塑性区约为12.9 mm,显示局部化的砂岩破坏过程;胶结应力的变化表明流速大于3 m/s时,增幅明显的剪应力加速了砂岩的剪切破坏,且颗粒平动和转动加剧,说明砂岩的胶结破坏严重,离散颗粒数呈量级增大,塑性区扩大明显。考虑流固耦合效应的三维数值方法能有效反映油井出砂的力学特性,当油藏流动对砂岩起控制作用时,出砂几率显著提高。

Mechanical response analysis of reservoir sandstone considering fluid-solid coupling effect

A numerical method based on 3-dimensional particle flow code (PFC3D) in cylindrical coordinate system was proposed to simulate the mechanical response of the reservoir sandstone. By comparing the simulation results with the triaxial test ones, the meso-mechanical parameters were determined, and then a perforation test model was built based on the fluid-solid coupling effect. The results show that macro stress of the sandstone can reflect the effect of oil flow rate on the increase of sandstone stress, and the stress is not greater than the peak strength of reservoir sandstone, the maximum plastic zone is 12.9mm. The results can describe the local failure process of sandstone. When flow rate is larger than 3m/s, obvious increase of the shearing stress will accelerate the shearing failure, the particle movement and rotation. The serious breakage of the bonds will result in the increase of dislodged particles by orders of magnitude and obvious expansion of the plastic zone. The 3-D numerical method considering fluid-solid coupling effect can reflect the mechanical characteristics of the sand production in the oil well better, and the probability of the sand production will be increased obviously when the oil flow rate controls the sandstone.