(1) (n.) Well Completions. A device fitted with a hinged collar and bowsprings to keep the casing orliner in the center of the wellbore to help ensure efficient placement of acement sheath around the casing string. If casing strings are cemented off-center, there is a high risk that a channel of drilling fluid or contaminated cement will be left where the casing contacts the formation, creating an imperfect seal. See: bow-spring centralizer, cementing, deviated hole, eccentricity. (2) (n.) Well Completions. A device used to keep a tool string in the center of the tubing, casing or wellbore. Tool centralization may be required for several reasons: to prevent the tool from hanging up on obstructions on the wellbore wall, to place fluid efficiently and to avoid excessive standoff. (3) (n.) Formation Evaluation. A device that helps to maintain the logging tool in the center of the borehole. On wireline tools such devices typically have three or more flexible bow springs. They may be mounted on the outside surface of the logging tool or else mounted in-line, between two cartridges or sondes. Some measurements, such as acoustic logs, respond better when the tool is centralized, while others, including induction logs, are better when eccentralized. Ant: Eccentralizer. See: Bow-Spring Centralizer, Sonde