Risk assessment on well control in deepwater drilling based on fault tree analysis

The harm of deepwater blowout is extremely serious, which may lead to useless wellbore and the disaster of rigs and staff. At present, the well blowout precaution and control technology in deepwater drilling is still a world-class technical problem for the petroleum industry both at home and abroad. Based on the fault tree analysis, the top events resulting in the accidents in deepwater drilling are discussed. Emphasis is laid on the discussion of the correlation between bottom events and their effect on the system. The probability of top events is also analyzed. All provides theoretical basis for reducing the deepwater well control accidents to the greatest extent. Based on the analysis on risks in deepwater drilling, the fault tree for the analysis of well control in deepwater is established, for which both qualitative analysis and quantitative analysis are conducted. Risk analysis shows that the critical factors affecting deep water well control are that the negative effect of design methods and operating failures exceeds the safety limits. It is significantly helpful to prevent blowout by reducing the occurrence probability of elementary events. The occurrence probability of elementary events is enhanced by one time, while that of blowout is increased by 10 times. In view of the risk elements in deepwater well control, measures of preventing blowout are put forward from the perspectives of technologies and equipments as well as the requirements on operating personnel.