The creation and presence of hydraulic fractures can cause casing failure both during and after the fracturing operations. During the fracturing operations, casing can fail under tension. The three main causes are thermal shrinkage of the casing, off-balance fracture growth, and pseudo-openhole environment. Other contributing factors are borehole inclination with respect to the fracture plane, and the quality of the cement bond.
Factors contributing to casing failure during well production include changes in in-situ stresses due to reduction in reservoir pressure,
off-balance fracture growth, formation layering and its inclination with respect to the wellbore, and shear strength of the interfaces.
The low formation shear strength along the propped fracture plane increases the probability of shear movement along it. The presence of the fracture will direct this movement towards the casing and can cause its shear failure. Rapid production pressure declines increase the shear stresses acting on the fracture plane and can cause movement along the fracture plane and ultimately casing failure.
These mechanisms causing borehole instability and associated casing failures will be discussed in this presentation, along with specific case histories.