气举柱塞偏心环空间隙流场数值分析

柱塞气举利用井底压差推动柱塞沿井筒运动,依靠柱塞与管壁间隙密封举升上部液体至井口,达到排水采气目的。目前,针对柱塞实际运动中发生偏心对气举密封的影响认识不够清晰,导致无法进一步优化柱塞密封结构和工艺参数。为此,利用气液两相分层流动数值计算方法,讨论了紊流槽内相含率和速度场变化规律,并分析其多道密封机理,获得不同偏心距导致的环空间隙差异条件下柱塞密封效果。研究结果表明：当柱塞与油管轴线处于同心状态作业时,根据特定场合设计的柱塞外壁紊流槽的密封效果可以满足气举要求,但由于柱塞运动时很难保证同心,随偏心距逐渐增大,柱塞与油管间隙增大导致其密封效果逐渐变差。在偏心距为0.9 mm时,窜气量相比同心状态增加140.33%,大量气体发生滑脱；偏心距为1.5 mm时,液体以0.29 kg·m-3的速度泄露至柱塞下方区域。故偏心状态对气举柱塞密封性能的影响不容忽视,对此修正柱塞偏心环空状态下的运动方程,以探究柱塞偏心后对启动压力和单次循环排液量的影响。

Numerical Analysis of Flow Field in Eccentric Annular Clearance of Gas-lift Plunger

The gas-lift plunger uses the pressure difference of bottom hole to drive the plunger to move along the wellbore, and uses the clearance between the plunger and the pipe wall to lift the upper liquid to the wellhead, so as to achieve the purpose of drainage and gas recovery. At present, the influence of eccentricity on seal is not clear enough in the actual movement of the plunger, which leads to the failure of further optimization of plunger seal structure and process parameters. The numerical calculation method of gas-liquid two-phase stratified flow was used to discuss the variation law of phase holdup and velocity field in turbulent flow groove, analyze the multi-channel sealing mechanism, and obtain the sealing effect of the plunger under the condition of different ring space gap caused by different eccentricity. The results show that the sealing effect of the turbulence groove on the outer wall of the plunger can meet the requirements of gas lift when the plunger axis coincides with the tubing axis. However, it is difficult for the plunger to ensure concentric motion, so with the increase of eccentricity, the increase of plunger and tubing clearance will lead to the gradual deterioration of the sealing effect of turbulent groove. When the eccentricity is 0.9mm, the gas channeling volume increases by 140.33% compared with the concentric state, and a large amount of gas slippage occurs. When the eccentricity is 1.5mm, the liquid leaks into the lower region at a rate of 0.29 kg·m-3. Therefore, the influence of eccentric state on the sealing performance of gas lift plunger cannot be ignored. The motion equation of eccentric plunger in annulus is modified to investigate the influence of eccentric plunger on starting pressure and single cycle drainage volume.