超深井溢流关井钻柱上顶机理及预防方法

Mechanism and prevention method of drill string up-lift during shut-in after overflow in an ultra-deep well

针对超深井溢流关井后钻柱在上顶力作用下存在冲出井筒风险的问题,建立钻柱上顶力计算模型,分析溢流关井期间钻柱上顶力动态变化特征,形成超深井溢流关井钻柱上顶风险管理程序。采用截面法和压力面积法分析溢流关井后钻柱受力情况,发现钻柱上顶力产生的根源是井内流体静液压力产生的虚拟力,当虚拟力与重力方向相反时,即为钻柱上顶力。采用环空多相流理论,考虑井筒续流效应和气体滑脱效应,分析了溢流关井期间井筒压力、溢流物的变化过程以及钻柱上顶力的动态变化特征。算例分析结果表明,钻柱上顶力的大小和方向与井筒内钻柱长度和关井时间有关,当井筒内钻柱长度小于临界钻柱长度、关井时间超过临界关井时间时,存在钻柱上顶的风险。给出了一套超深井发生溢流后预防钻柱上顶的方法和流程,使钻柱上顶风险管理更加严谨和科学。

Drill string will sustain large up-lift force during the shut-in period after gas overflow in an ultra-deep well,and in serious case,it will run out of the wellhead.A calculation model of up-lift force was established to analyze dynamic change characteristics of the up-lift force of drill string during the shut-in period,and then a management procedure for the up-lift risk during the shut-in period after gas overflow in the ultra-deep well was formed.Cross section method and pressure area method were used to analyze the force on drill string after shut-in of well,it was found that the source of up-lift force was the'fictitious force'caused by the hydrostatic pressure in the well.When the fictitious force is in the opposite direction to the gravity,it is the up-lift force.By adopting the theory of annular multiphase flow,considering the effects of wellbore afterflow and gas slippage,the dynamic change of the pressure and fluid in the wellbore and the up-lift force of drill string during the shut-in period were analyzed.The magnitude and direction of up-lift force are related to the length of drill string in the wellbore and shut-in time,and there is the risk of up-lift of drill string when the length of drill string in the wellbore is smaller than the critical drill string length or the shut in time exceeds the critical shut in time.A set of treatment method and process to prevent the up-lift of drill string is advanced during the shut-in period after overflow in the ultra-deep well,which makes the risk management of the drill string up-lift in the ultra-deep well more rigorous and scientific.