针对经典瞬变流模型无法模拟气井水锤效应问题,基于水锤效应机理与多相流理论,建立了多相流气井瞬变流数学模型;通过将油管柱的造斜部分进行单独处理,采用特征线法进行数值求解,实现了气井瞬变流的模拟计算。研究结果表明：阀门关闭时开度系数越大,井口压力的峰值越大,波动压力的变化幅度越平缓,压力突变区越不明显,在保证不超过油管最大关井压力的前提下,使用较大的开度系数可减小压力波的冲击;截面持液率越大,压力波速越大,传播周期越短,波动压力的变化幅度越大,压力越大,实际生产中可通过调整生产参数得到合适的持液率,控制波动压力的大小和变化幅度,减小水锤压力的冲击;采气树阀门关闭所用时间增加,井口的最大波动压力值减小,峰值出现的时间也相应滞后,压力突变区逐渐消失,阀门关闭时间越短,压力波的传播速度越快。实例模拟计算证实气井瞬变流模型可以优化合理的阀门开度系数和关阀时间,减小水锤冲击对井口装置和油管造成的危害,保障井筒完整性。图10表1参23
As the classical transient flow model cannot simulate the water hammer effect of gas well, a transient flow mathematical model of multiphase flow gas well is established based on the mechanism of water hammer effect and the theory of multiphase flow. With this model, the transient flow of gas well can be simulated by segmenting the curved part of tubing and calculating numerical solution with the method of characteristic curve. The results show that the higher the opening coefficient of the valve when closed, the larger the peak value of the wellhead pressure, the more gentle the pressure fluctuation, and the less obvious the pressure mutation area will be. On the premise of not exceeding the maximum shut-in pressure of the tubing, adopting large opening coefficient can reduce the impact of the pressure wave. The higher the cross-section liquid holdup, the greater the pressure wave speed, and the shorter the propagation period will be. The larger the liquid holdup, the larger the variation range of pressure, and the greater the pressure will be. In actual production, the production parameters can be adjusted to get the appropriate liquid holdup, control the magnitude and range of fluctuation pressure, and reduce the impact of water hammer effect. When the valve closing time increases, the maximum fluctuating pressure value of the wellhead decreases, the time of pressure peak delays, and the pressure mutation area gradually disappears. The shorter the valve closing time, the faster the pressure wave propagates. Case simulation proves that the transient flow model of gas well can optimize the reasonable valve opening coefficient and valve closing time, reduce the harm of water hammer impact on the wellhead device and tubing, and ensure the integrity of the wellbore.
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