By examining the reduced axial force, Fa*, in a casing string, the operating conditions under which the uncemented portion of the casing will buckle are defined. This leads directly to methods of preventing buckling.
The axial force is influenced by changes in pressures and temperature that can occur once the string has been constrained by cementing.
The actual axial force, Fa, at any depth, z, in a casing string above the top of cement usually depends on;
- the cemented-in buoyant weight
- changes in fluid gradients and surface pressures from the cemented-in in buoyant weight
- changes in temperature from the cemented-in in buoyant weight
- changes in surface force from the cemented-in in buoyant weight.