When the producing zone of interest resides in close proximity to another zone containing water or natural gas, too often interzonal communication interferes with production. These are areas where primary cementing is not always successful due to reservoir or formation characteristics. Over time communication begins in the annulus impairing production. Traditional methods of perforating and remedial cement can be risky. Controlled CET can be accurately applied between the desired and undesired intervals to restrict or shut-off interzonal communication without risking production impairment.