压裂气井支撑剂回流影响因素数值模拟研究

Numerical Simulation Study on the Influencing Factors of Proppant Flowback in Fractured Gas Wells

摘要: 支撑剂回流是压裂气井开采过程中的核心工程问题之一。生产流速对支撑剂回流有着重要影响，流速过快会导致支撑剂大量脱落回流，引起人工裂缝闭合塌陷、导流能力严重下降及地面管线冲蚀破坏；而流速过慢则会加剧地层伤害，制约气井产能充分释放。本文针对压裂气井生产工况，基于计算流体力学与离散颗粒元(CFD-DEM)双向流固耦合仿真方法，建立了长宽高为200 mm × 2 mm × 30 mm的三维数值裂缝流动模型。以Case 0 (支撑剂密度2560 kg/m³、粒径0.425 mm、入口流速0.5 m/s)为基准工况，严格设置了涵盖支撑剂密度(1650、2560、3300 kg/m³)、颗粒粒径(0.212、0.300、0.425、0.850 mm)及入口流速(0.2、0.3、0.5、0.6、0.7、0.8 m/s)的11组数值模拟计算工况(Case 0 ~ Case 10)，系统分析了裂缝内气相冲刷通道过程、影响因素敏感性以及回流质量特征。研究结果表明：通道边界流速达到临界起动流速是诱发颗粒起动回流的微观主因；随着入口流速从0.2 m/s增加到0.8 m/s，支撑剂回流相对质量呈现非线性加速，0.5 m/s附近存在显著的稳定界限；增大颗粒粒径(0.212 mm至0.850 mm)和提高颗粒密度(1650 kg/m³至3300 kg/m³)均能大幅削减回流总量。本研究为控制支撑剂回流，科学设计返排及生产参数、提高压后效果有着重要指导意义。

Abstract: Proppant flowback is one of the critical engineering challenges encountered during the production of fractured gas wells. Production flow velocity has a significant influence on proppant flowback. Excessively high flow velocity can induce substantial proppant mobilization and flowback, resulting in propped-fracture closure and collapse, severe reduction in fracture conductivity, and erosion damage to surface flowlines. In contrast, excessively low flow velocity may aggravate formation damage and limit the effective release of gas-well productivity. In this study, a three-dimensional numerical fracture-flow model with dimensions of 200 mm × 2 mm × 30 mm was established for the production conditions of fractured gas wells using a two-way coupled computational fluid dynamics-discrete element method (CFD-DEM). Case 0, with a proppant density of 2560 kg/m³, particle diameter of 0.425 mm, and inlet velocity of 0.5 m/s, was selected as the baseline case. A total of 11 numerical simulation cases (Case 0 ~ Case 10) were systematically designed by varying proppant density (1650, 2560, and 3300 kg/m³), particle diameter (0.212, 0.300, 0.425, and 0.850 mm), and inlet velocity (0.2, 0.3, 0.5, 0.6, 0.7, and 0.8 m/s). The gas-phase erosion and channelization process within the fracture, the sensitivity of proppant flowback to the governing parameters, and the characteristics of flowback mass were systematically investigated. The results show that the attainment of the critical incipient-motion velocity at the channel boundary is the primary microscopic mechanism responsible for proppant mobilization and subsequent flowback. As the inlet velocity increased from 0.2 to 0.8 m/s, the relative proppant flowback mass exhibited a nonlinear accelerating trend, with a distinct stability threshold occurring at approximately 0.5 m/s. Increasing the particle diameter from 0.212 to 0.850 mm and the proppant density from 1650 to 3300 kg/m³ both substantially reduced the total flowback mass. These findings provide valuable guidance for controlling proppant flowback, optimizing flowback and production parameters, and improving post-fracturing stimulation performance.