Investigation of Lost Circulation and Wellbore Strengthening During Drilling Petroleum Wells: An Overview

Lost circulation is the partial or complete loss of drilling fluid into a formation. It is among the major non-productive time events in drilling operations. Most of the lost circulation events are fracture initiation and propagation problems, occurring when the fluid pressure in a wellbore is high enough to create fractures in a formation. Wellbore strengthening is a common method to prevent or remedy lost circulation problems. Although many successful field applications have been reported, the fundamental mechanisms of wellbore strengthening are still not fully understood. There is still a lack of functional models in the drilling industry that can sufficiently describe fracture behavior in lost circulation events and wellbore strengthening. A finite-element framework was first developed to simulate lost circulation while drilling. Fluid circulation in the well and fracture propagation in the formation were coupled to predict dynamic fluid loss and fracture geometry evolution in lost circulation events. There are two common wellbore strengthening treatments, namely, preventive treatments based on plastering wellbore wall with mudcake before fractures occur and remedial treatments based on bridging/plugging lost circulation fractures. Two analytical models were developed for the investigation of preventive and remedial wellbore strengthening. The models developed and analyses conducted in this paper present a useful step towards the understanding of the fundamentals of lost circulation and wellbore strengthening, and provide improved guidance for lost circulation prevention and remediation.