气井柱塞举液机理CFD模拟及工艺参数优化

CFD Simulation and Process Parameter Optimization of Gas Well Plunger Lifting

目前关于柱塞举液机理的认识不够清晰,这对柱塞高效举液工艺参数及工具结构的进一步优化造成不利影响。为此,采用VOF (Volume of Fluid)流体模拟方法对柱塞举液上行过程中的气液两相流场进行CFD模拟,对柱塞气液流动过程及密封原理进行探讨和分析,并对不同柱塞上行速度及不同紊流槽尺寸下的流场分布进行模拟对比,确定柱塞运行的最佳条件。研究结果表明:柱塞上行过程紊流槽中液体与气流间的相互作用阻碍了气体向柱塞上端的窜流及液体向下的泄漏;气流进入每级紊流槽形成漩涡,使部分动能转化为内能耗散达到密封效果;柱塞上行速度较低时,流场中无漏液,窜气量随上行速度增加而减小;上行速度较高时,紊流槽中全为液相,漏液量随上行速度增大而增加;模拟范围内密封最佳的柱塞运行速度为4. 0~4. 5 m/s;当紊流槽宽度与深度相等时其密封作用最差,当紊流槽宽度为深度的2倍时,液体与气流间的相互作用最强烈,密封效果最佳。研究结果可为柱塞气举工艺制度及参数的优化提供指导。

At present,the insufficient understanding of the plunger lifting mechanism adversely affects the further optimization of the plunger lifting parameters and the tool structure.To address the problem,the VOF(Volume of Fluid)fluid simulation method is used to perform a CFD simulation of the gas-liquid two-phase flow field during the upward movement of the plunger.The gas-liquid flow process and sealing principle of the plunger are discussed and analyzed.The upward velocity of the plunger and the flow field distribution under different turbulent groove dimensions are simulated and compared to determine the best conditions for the plunger to operate.The study results show that the interaction between the liquid and the gas in the turbulent groove during the upward movement of the plunger prevents the gas from channeling to the upper end of the plunger and the downward leakage of the liquid.The gas enters each stage of the turbulent groove to form a vortex,which converts part of the kinetic energy into internal energy dissipation,achieving the sealing effect.When the upward velocity of the plunger is low,there is no liquid leakage in the flow field,and the amount of channeling gas decreases with the upward velocity.When the upward velocity is high,the turbulent groove is full of liquid phase.The liquid leaking volume increases with the upward velocity.The optimum plunger operating speed for sealing in the simulation range is 4.0 to 4.5 m/s.The sealing effect is the worst when the width of the turbulent groove is equal to the depth.When the width of the turbulent groove is 2 times of the depth,the interaction between liquid and gas is the strongest,resulting in the best sealing effect.The study results can provide guidance for the optimization of the plunger gas lift system and the operation parameters.