Oil and Gas Glossary

zonal isolation

Refers to the state or quality with which the fluids in one permeable zone can be kept separate from those fluids of another. Zonal isolation is created and maintained in the well bore by cementing the production string in place and by appropriate use of casing plugs and packers. Beyond the well bore radius and inside the formations, zonal isolation is a function of the existence of permeable barriers such as impermeable shale members, dense sediments, or cap rock. The quality of zonal isolation is directly related to the quality of the cement and bonding which is found between casing, cement sheath, and formation; and to the degree of or lack of permeability of the members which can serve as permeability barriers.