基于CFD的气举柱塞排液机理与运行规律分析

Analysis of gas lift plunger drainage mechanism and operation law based on CFD

柱塞气举是实现低产气井排水采气的有效措施。目前柱塞的排液机理仍不明确,极大限制了柱塞结构与工艺参数的优化。采用VOF模型结合动网格方法,对柱塞运动流场进行CFD数值模拟,分析柱塞气举过程中气液流动规律、密封机理与柱塞运行规律。结果表明,上行过程中,气体在柱塞与井筒的环隙之间,气体上窜时产生的绕流阻力是柱塞上行的主要动力,窜气必然存在,液体泄漏较少,密封环槽内涡流不明显;下行过程中,槽内形成较强涡流。无论上行还是下行,柱塞均会快速达到受力平衡。在井况相近情况下柱塞的绕流阻力系数基本不变,可根据井况采用平衡速度估算柱塞的总体运行时间。

Plunger gas lift is an effective measure to achieve drainage gas production in low-yield gas wells.At present,the discharge mechanism of the plunger is still unclear,which greatly limits the optimization of the plunger structure and process parameters.The FOF model combined with the dynamic grid method is used to simulate the CFD numerical simulation of the plunger motion flow field,and the gas-liquid flow law,sealing mechanism and plunger operation law during the plunger gas lifting process are analyzed.The results show that in the upward process,the gas is between the annular gap and the wellbore,and the circumvention resistance generated when the gas is channeled is the main driving force of the plunger to ascend,and the channeling gas must exist,the liquid leakage is less,and the vortex in the sealing ring groove is not obvious.During the downward process,strong eddies form in the trough.Whether upward or downward,the plunger quickly reaches force balance.The winding resistance coefficient of the plunger is basically unchanged when the well conditions are similar,and the overall running time of the plunger can be estimated according to the equilibrium speed according to the well conditions.