CASING BUCKLING
Buckling in a tubular string results in a helical configuration in which spiralling increases with distance below the neutral point. When a casing string is only partially cemented, it can become unstable and consequently, buckle and deflect laterally. This is especially true if the casing is exposed to increased mud weight and high circulating bottom hole temperatures as is the case when drilling proceeds for several thousand feet below the original shoe into a geo-pressured interval.
Buckling and deflection in the string produces doglegs in the pipe and subsequent drilling and tripping operations rapidly wear the inside of the casing across the buckled interval and can ultimately lead to casing failure which is very costly and difficult to rectify once it occurs. Other disadvantages of buckled casing are: difficulty in running drilling and completion operations, failure of casing couplings due to deformation, and breakage of threads.
The purpose of the next section is to provide a basic understanding of the stresses which lead to casing buckling and methods for its prevention.