关键词: 柱坐标系, 三维颗粒流数值模型, 流-固耦合效应, 出砂细观机制, 细观特征

Abstract: Research on mechanism of sand production has been the key topic to improve the oil production and reduce the oil extraction cost; however, current investigations are mainly based on rock macromechanical theory and methods; and these achievements cannot comprehensively reflect initiation and propagation of the sand production. Considering physical property of the sand reservoir and real characteristics of the perforation test, 3-Dimensional numerical model based on PFC3D under cylindrical coordinate system from a geomechanics prospective was established to research the fluid-solid coupling effect and the micromechanism of sand production. The comparison with theoretical results shows the feasibility of the forward 3-Dimensional micro numerical model; and the model could simulate the fluid flow and fluid-solid coupling effect in the process of sand production. Based on the above numerical model, simultaneously considering pressure gradient force and drag force, research on initiation and propagation of the sand production was carried out based on PFC3D considering different fluid flowing conditions. The figures about simulated stress distribution indicate that fluid flow affecting the sand mechanical characteristics should not be neglected during oil extracting; and under the same conditions, the greater the flow rate is, the more the bonds between the particles are; and the larger the sandstone plastic zone is, and also the greater the probability of the sandstone broke and sand production is. In addition, there were research achievements about the initiation and propagation of the broken parallel bond and magnitude of the particles rotation considering different cases. The figures show that under the same conditions, the larger the flow rate is, the greater the range of the plastic zone and the particle rotation was to result in more particles losing restraints; and also the more volume of the sand production. The above numerical results explained the same developing trend comparing the two kinds of figures about micro characteristics of the particles between the figures about macro stress distribution, and the results indicated that the forward micro numerical model could simulate the sanding mechanism and also provide a new thought to predict the sand volume and control the sand production.

Key words: cylindrical coordinate system, 3-dimensional particle-based distinct element model, fluid-solid coupling effect, micromechanism of sand production, micromechanical characteristics