The cement sheaf behind the casing of the petroleum well is subject to stress in production or injection conditions, created by the bottom-hole pressure across the perforated reservoir.
This can lead to cement break and creating a channel between the perforated reservoir and non-perforated reservoir.
Predictive model for cement failure under pressure drop between perforated reservoir and non-perforated reservoir is given at Cement Failure @ model an depends on the difference between BHP, formation pressure in perforated and non-perforated formations and the distance between them..
See Also
Petroleum Industry / Upstream / Rock Geomechanics