Safety analysis of deepwater well control based on STAMP/STPA

Key words:  deepwater  well control  safety analysis  restriction  accident model and process

Abstract:

Traditional methods of safety analysis cannot solve the evaluation problem of the abnormal interactions among elements of complex systems. In view of the complex and dynamic characteristics of deeper well control, the safety analysis of deepwater well control during the drilling process is regarded as a system control and feedback problem in this study. Based on the accident model on the system theory, and the STAMP model, we use the STPA safety evaluation method to establish the control interaction model and feedback control loop of the well control system. In the model, the system safety risks and restrictions are identified. Then the control structure of the safety-related is defined, and the key factors which contribute to unsafe control behaviors are analyzed. Using the dynamic multiphase simulation software OLGA, and adopting the STAMP/STPA as the criterion, we analyze the process of well control and simulate the unsafe control behaviors during the deepwater drilling. The dynamics analysis of the well control safety is performed, where the case without control after well kill and the delay of control from shut in to well kill are taken as examples. The results show that the STAMP/STPA method is an effective solution to evaluate the safety of deep water well control from the perspective of control and feedback. The rational control can prevent accidents occurrence and escalating, which ensured the system safety in the certain time horizon, by modeling the process of well kick, shut in and well kill. The results also demonstrate that the method is available and useful for the safety analysis of deepwater well control.