南海深水海域避台风期间井控安全作业周期研究

Well Control Safety Operation Cycle during Typhoon at Deep Waters of South China Sea

我国南海深水海域夏季台风活动频繁,在撤离平台避台风期间,井筒中流体长时间处于静止状态,如果气体侵入井筒并上升至风暴阀处,给解封、开井作业带来较高的井控风险。为此,针对南海避台期间井控作业的特点,根据钻井液黏度、密度、表面张力、气泡直径以及壁面效应等因素对气体上升速度的影响,对拖曳力系数模型进行了修正,建立了避台风期间井筒内气体上升速度的计算模型,并对所建模型进行了验证,验证结果表明,模型计算结果与现场实测数据吻合较好。利用所建气体上升速度模型对避台风期间影响气体上升速度的因素进行了分析,结果表明,气体上升速度随井深的减小而增大,随钻井液密度增大而增大,随钻井液黏度增大而减小,随地层孔隙度增大而增大。结合我国南海实际情况,绘制了不同井眼条件下的安全作业周期图版,现场工作人员可通过该图版判断风暴阀下是否圈闭有高压气体,从而有针对性地采取井控措施。

Typhoons frequent deep waters of South China Sea in summer. Drilling fluid in the well will stay for a long time when evacuating from platform during typhoon landing, and gas channeling into well- bore and rising up to the storm valve can bring high risk to well control during well unseal and open opera- tions. Therefore, in view of the characteristics of well control operations during typhoon in the South China Sea,a variety of factors that affect the rising speed of the gas were considered,including drilling fluid vis- cosity,density, surface tension, bubble diameter and wall effect, etc. The drag coefficient model was modi- fied to calculate the rising speed of the gas in the wellbore during typhoon. The model that calculates the rising speed of the gas was verified and the results showed a good agreement with field data. Factors that affect the rising speed of gas were analysed by applying the model, the results showed that gas rise velocity would go up with depth decrease and the drilling fluid density increase, and would go down with the in- crease of drilling fluid viscosity, but increase with formation porosity increase. According to the actual situ- ation in the South China Sea, plots of safe operating cycle under different borehole conditions were drawn so that field staff could determine from these plots whether storm valve traps high-pressure gas, and take pertinent measures of well control.