Well casing is subjected to a wide variety of loading mechanisms that can cause temporary or permanent deformations. These deformations can be due to geological processes or well operations. They can impair or prevent access to the full depth of the well or compromise the pressure integrity. They can occur instantaneously or progress over many years.
Many historical well workover reports have reported casing deformations as “casing collapse” when a tool string cannot pass by a “tight” interval. In fact, collapse is not a common deformation mode,with shear and buckling deformations being much more likely modes of well failure.
Some of the most common scenarios that lead to well failures for each deformation mode include:
Shear – When the Earth Moves
- Water injection
- Steam injection
- Overburden subsidence
- Faults and slip planes
- Margins of mobile salt bodies
Buckling – When You Push on a Rope
- Pore pressure reduction
- Shallow water flow
- Solids production
- Permafrost thaw
Collapse – When You Can’t Take the Pressure
- Heating of trapped annular fluid
- Salt/shale squeeze
- Overpressure during well operations
Conventional casing inspection logs such as multi-finger caliper or ultrasonic profilers can show that there is wellbore restriction but usually do not provide enough information to determine the type of deformation and its root cause.
Information from these logs can be used in C-FER’s WellXplore software to characterize these deformations and provide detailed measurements of the deformed pipe shape to help well operators decide on appropriate courses of actions to maximize the remaining life of the well.
A series of articles is available that describes the most common forms of deformations that have been observed with WellXplore including: Shear, Buckling and Collapse.