Study of Risk Matrix for Overflow-Backpressure-Based Deepwater Managed Pressure Drilling

Overflow accidents are frequent in deepwater managed-pressure drilling, and the monitoring basis and control methods of risks are vague, necessitating the establishment of a suitable risk matrix. Based on the traditional risk matrix analysis method, this paper establishes a overflow-backpressure risk matrix with overflow size and backpressure threshold as judgment criteria, and formulates 11-level backpressure application plans and backpressure application calculation models. The results show that the overflow-backpressure risk matrix with overflow size and backpressure threshold as judgment criteria meets the requirements of deepwater managed-pressure drilling design and can significantly determine the risk level of overflow occurrence. The formulated backpressure application calculation model refines the backpressure control situation of managed-pressure drilling and can apply different backpressure according to different risk levels. After applying risk control measures, the maximum allowable drilling speed and backpressure in different working conditions of the 3950-4130 m wellbore section were designed on-site at well A1, and the risk level was reduced to 0. This overflow-backpressure risk matrix can classify and control the risk of overflow in deepwater managed-pressure drilling.