Common Indicators of Wellbore Instability:
Encountering wellbore instability while drilling is very common. It can happen in many different formations due to various reasons. An unstable wellbore can cause hole collapse, hole enlargement, hole bridging, loss of hole, stuck downhole tools, improper well evaluation, etc. It can also compromise well integrity if proper annular isolation is not achieved due to poor casing cementation. The good news is that the wellbore instability phenomenon is very well understood in the industry and can be mitigated to minimize the time & cost impact with proper pre-planning and appropriate measures. Common indicators of wellbore instability are:
· Over gauge hole
· Under-gauge hole
· Excessive cuttings
· Excessive caving
· Gradual increase in torque and drag
· Higher circulating pressure
· More than calculated fill-up volume of drilling fluid
· More than calculated cement volume requirement