柱塞气举动态模型的建立

为了分析柱塞举升过程中气体压力变化情况和柱塞的运动状态,将柱塞运行周期划分为柱塞上行、气井续流生产、柱塞下降与压力恢复3个连续过程.利用动量平衡方程,研究了柱塞和液体段塞的运动特征,应用质量守恒原理研究了柱塞气体压力的动态变化.在讨论柱塞上、下端面气体压力时,考虑了气体从地层流入井筒再由井筒向外产出的影响以及井筒积液高度对气井产量的作用.在理论模型建立过程中,将所研究段气体分割成若干控制体,并假定在时间单元内控制体的参数是恒定的,建立了多种影响因素下的柱塞和液体段塞运动方程,给出了油、套压计算方法,编制了柱塞气举动态模型计算程序.经现场生产实例计算证实,该模型可靠性较高,为柱塞气举优化设计提供了理论基础.

Establishment of dynamic model for plunger gas lift

In order to study gas pressure variety and plunger movement during plunger lifting, the circulate cycle of plunger was divided into three continuous stages of upward travel of plunger, opening of sales valve after plunger arrived, falling of plunger and resuming of pressure. The movement features of plunger and liquid column were studied by using the momentum conservation equation. The change of gas pressure during movement of plunger was investigated with the mass conservation law. The gas pressures in the upper and below parts of plunger were discussed, in consideration of the effects of gas came from gas reservoir and output from well bore in the gas expanding equation and the effects of liquid loading in well bore on gas production of a gas reservoir. When the mass conservation law was utilized to establish theoretical models, the gas volume in the studied section was divided into a lot of control volumes, and the factors of controlled volume were assumed as invariable with time increment. A lot of movement equations for plunger and liquid column were given, and the dynamic models for calculating casing pressure and tubing pressure were established on the analysis of different factors. The calculation procedures of the models were accomplished. The case history computation in-situ approves that the model has good dependability and can provide a theoretical base for optimum design of plunger gas lift.