Application of Fault Tree Analysis to Risk Assessment of Lost Circulation Hazards in Drilling

Lost circulation is one of the most difficultly predicted and controlled drilling accidents.Based on accident-causing theory,the conceptual model of drilling lost circulation was developed,the risk sources of drilling lost circulation were classified into geological conditions,bottom hole pressure,lost circulation factors and salvage failure.On the basis of fault tree analysis,the fault tree model of drilling lost circulation was developed and the method to assess the risk of lost circulation was proposed.Taking Dong An NO 1 well as an example,the four aspects of lost circulation were analyzed;the lost circulation fault tree model of Dong An was constructed.The most dangerous factor of lost circulation was geological condition according to the least cut-set and the least path-set.Suggestions were given to prevent lost circulation,including paying more attention to geological conditions while designing,establishing rescue mechanism and operating follow regulations.It shows that the fault tree analysis can be effectively used in safety assessment of drilling lost circulation accidents.