Wellbore loss is a significant risk threatening the quality and safety of bridge plugging + perforation in coal-bed methane(CBM).So,combined with complex engineering cases,some simulation was conducted on well-bore loss based on achieved awareness on perforation from basic theoretical studies and application practices,as well as numerous ex-periences from CBM operation in Shanxi Province.Results indicate that(i)the loss with too rapid velocity may lead to a strong wa-ter hammer effect on the end face of bridge plug during plug sitting,further to cause the weak point of cable he-ad to break off and downhole tools to fall into a well;and(ii)the phenomenon of empty wellbore induced by strong loss can eas-ily result in ball-drop failure and secondary engineering complexities.It is concluded that changes in both fluid flow rate in-side casing and liquid level in wellbore during bridge plugging + clustering perforation in CBM reservoirs in case of well-bore loss may seriously affect the key issues such as pumping rate,bridge plug sitting,and soluble ball drop at wellhead;and tak-en leakage position and degree into account,boundary conditions under safe operation are determined through simulation calcula-tion,and then countermeasures against wellbore loss are made,so that the safety of bridge plugging + perforation can be ensured.
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