压井期间水平井扩径段气体运移规律研究

Law of gas migration in the enlarged section of horizontal wells during well killing

深水水平井钻井水平段普遍存在井眼扩大现象,发生气侵时气体会聚集在扩径段形成气体“口袋”,引发井控难题。通过设计水平井扩径段井筒多相流动模拟实验系统,开展了气体聚集及运移实验,得到了含气体“口袋”的水平井筒中气液两相流动规律。实验结果表明:扩径段中的气体“口袋”在排出时存在一临界液相排量,当液相排量小于临界值时,聚集气体无法被排出;当液相排量超过该临界值时,聚集气体被逐渐排出;气体的平均排出速度随着液相速度的增加而增加。在实验研究基础上,通过理论分析建立了考虑液相黏度、变径程度及液相排量影响的水平井扩径段聚集气体气相运移速度模型,与实验数据对比该模型预测误差在±10%以内,可满足工程计算要求。本文研究成果可为压井期间水平井扩径段聚集气体的控制提供理论指导。

Borehole enlargement is common in the horizontal section of deep-water horizontal wells.If gas kick occurs in the wellbore,gas"pockets"will be formed in the enlarged section due to gas gathering,which may cause difficulties in well control.In this paper,an experimental system of multi-phase flow simulation in the enlarged section of horizontal wells was built to conduct a gas gathering and migrating experiment,obtaining the law of gas-liquid two-phase flow in the horizontal wells with gas“pockets”.The results show that there is a critical displacement of liquid for squeezing the gas“pocket”out in the enlarged section,and the gas cannot be pushed out when the liquid displacement is below the critical value.When the liquid displacement exceeds the critical value,the gathered gas is gradually discharged.The average discharging velocity of the gas increases as the increase of liquid velocity.Based on the experimental study,a model of migrating velocity of the gathered gas in the enlarged section of horizontal wells was established by theoretical analysis considering the effects of liquid viscosity,degree of diameter ratio change and liquid displacement.Compared with the experimental data,the prediction error of the model was within±10%,which met the requirement of engineering calculation.The research can provide theoretical guidance for the control of gas gathering in the enlarged section of horizontal wells during well killing.