A Five-Step Bullheading Killing Well Control Method for Fractured Formations without a Safety Pressure Window

While using conventional killing well control methods to deal with the gas kick in fractured formations without a safety pressure window,rapid lost circulation and blowout may occur again.Based on the guideline for the safe control of wellbore pressure and establishment of safe pressure window,a five-step bullheading killing well control method was proposed to handle the gas kick in fractured formations without a safety pressure window,including squeezing diversion,stable bullheading,stepwise halting,pressure stabilizing with hoisted filling,and leakage plugging under pressure.The new approach presented the calculation methods for the key parameters,such as flow rate of killing fluid,leakage pressure difference,casing pressure and safety pressure window etc.The five-step bullheading killing well control method has been applied in Tarim Oilfield since 2006,and handled overflow for 1 138 times and 38 times of well control risks,improving the success rate of well killing significantly.The research results showed that the five-step bullheading killing well control method could effectively control the wellbore pressure and realize the safe drilling in the fractured formation with the coexistence of blowout and lost circulation.