Historically, the sole purpose of oil and gas wellbore casing is to provide a secure conduit for the production of hydrocarbons to surface, retain the integrity of the borehole through native rock, and to prevent communication between the outside of the casing (annulus) with the inside of the casing in either direction except as required for hydrocarbon production, injection or disposal.

Over time and for a variety of reasons, the cement seal in the casing annulus breaks down allowing vertical communication of natural gas or fluids. This can result in unwanted and undesirable interzonal communication which can interfere with production efficiency or result in methane leakage to surface, an operational and environmental hazard.

CET uses powerful, hydraulically controlled casing expansion to expand casing in a uniform manner without damaging it to create a seal in the annulus or reseal leaking cement.

Of significant importance for the long-term integrity and operational effectiveness of the wellbore, controlled CET does not put holes in the casing nor restrict the normal use of the wellbore. Current methods of re-sealing the casing annulus involve perforating, puncturing or even removal by section milling intervals of casing. Should the remedial cementing that take place thereafter fail, the wellbore suffers a permanent loss of casing sealing integrity.