基于二维孔隙网络模型的悬浮颗粒微观尺度滞留规律及渗流场特征

Nanomicron heterogeneous topic: Pore size suspended particle retention law and seepage field characteristics

  • 摘要: 油气田开发是典型的多相渗流过程,在长期并持续的开发过程中,注水、气驱、化学驱及压裂等技术都会导致携带来的矿物颗粒及储层内原有喉道的砂体颗粒逐渐松散并脱落,造成储层孔隙中的迁移及堵塞,继而影响储层的动用及最终采收率. 因此,研究悬浮颗粒在多孔介质中迁移与滞留过程及流场特征有重要意义. 然而,现有针对悬浮颗粒在多孔介质中迁移与滞留的研究主要关注颗粒的迁移和滞留对渗透率的损害,没有体现颗粒运移的过程,也不能反应孔隙网络中颗粒堵塞和流场变化的关系. 为探究悬浮颗粒在多孔介质内的流场特征,本研究利用微观可视化模型及微观粒子图像测速技术(Micro-Particle image velocimetry,简称为Mirco-PIV)分析了在二维孔隙网络中悬浮颗粒的滞留特征及相互关系,并揭示了流场的变化规律. 实验结果表明,初期主通道流速更高,但由于主通道颗粒滞留量(6.5 μg·μm−2)比边界区更多(2.4 μg·μm−2),颗粒续注入导致主通道流速降低,扰乱原有流场导致“斑”状流场出现,也使主通道(110 μm·s−1降低至41 μm·s−1)在中期流速低于边界区(67 μm·s−1降低至45 μm·s−1). 这也表明高流速区更有效的输运了颗粒. 滞留的分布特征观察到主要滞留在了边壁附近,较高浓度条件下还会在主通道内产生聚集现象,这些都导致了对孔隙的有效封堵. 本文首次提供了颗粒和流场互动过程,给出二维孔隙条件下可视化的直接的证据. 此外,本文还得出了颗粒分布特征,并总结出滞留靠近边壁、流动有效半径变窄及主通道高浓度的聚集问题,是导致封堵的核心机理,为进一步颗粒滞留理论的完善提供参考.

     

    Abstract: The development of oil and gas fields involves a typical multiphase percolation process. Over time, techniques such as injection, gas flooding, chemical flooding, and fracturing can cause mineral and sand particles in the original reservoir throat to gradually loosen and fall off. This particle loosening can adversely affect reservoir exploitation and reduce recovery efficiency. Therefore, studying the migration and flow field of suspended particles within porous media is considerable. However, current studies mainly address how particle migration and retention affect permeability and often overlook the dynamics of particle migration and their impact on flow fields within pore networks. The microscopic visualization model and microparticle image velocimetry (Mirco-PIV) technology were used to analyze particle retention and flow field changes in the main channel and boundary region of the two-dimensional porous glass model, and the laws were summarized. Results show that while initial flow velocity is higher in the main channel, particle retention in the main channel is more pronounced than that in the boundary region. Continuous particle injection reduces the flow velocity in the main channel, disturbing the original flow field and creating a “spot” flow field. Eventually, the main channel experiences a lower flow rate in the medium term than the boundary region, indicating that particles are transported more efficiently in high-flow zones. Retention mainly occurs near side walls, with high concentrations, leading to aggregation in the main channel, effectively plugging pores. Previous studies did not account for retention, aggregation, and interweaving. To our knowledge, this paper provides new insights into the interaction between particles and flow fields, offering direct visual evidence for two-dimensional conditions. As particles are injected, high flow rates transport a larger number of particles, increasing the possibility of retention and subsequently decreasing flow rates. This illustrates the interaction mechanism between particles and flow fields over time and space. Regarding flow velocity, the trends in the main channel and boundary region are inconsistent. As particles are continuously injected, the trunk road of the main channel changes, whereas the boundary region remains unaffected. In addition, particle distribution characteristics show that the core mechanism of blockage involves retention near the side wall, a reduction in the effective flow radius, and high concentration areas in the main channel. Current theories do not adequately address these issues and should be revised accordingly. The study used a combination of microscopy and micro-PIV to explore the retention and flow field of suspended particles in porous media, uncovering critical variations in these processes.

     

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