Casing Centralizer

Types of Casing Centralizer

Three designs dominate. The bow spring centralizer consists of curved steel springs welded or hinged to two end collars. It is flexible, so it compresses through tight spots and then springs back, and it is the standard choice for most vertical and moderately deviated wells. The rigid centralizer has a solid body with straight or spiral blades machined or cast into it. It provides much higher restoring force and is used in horizontal and highly deviated wells where the casing tends to lie on the low side of the hole. The solid body centralizer is a variant of the rigid type with a fully continuous body and no welded components, offering the highest strength and the best performance in the most demanding wellbores, at a higher cost. Selection depends on hole angle, dogleg severity, casing weight and the required standoff.

Spacing and Placement

Centralizer spacing is normally determined by a cementing simulation that balances standoff against drag. The general principle is that centralizers are placed most densely across the producing interval and any section where cement isolation is critical, and less densely elsewhere. In vertical wells, spacing of one centralizer per joint is typical. In deviated wells spacing must be reduced, and in horizontal sections a rigid or solid centralizer every joint or every other joint may be required. The critical check is drag: too many centralizers, or centralizers with too high a restoring force, can increase running drag to the point where the string cannot be run to depth. Always confirm the spacing calculation against the actual hole geometry before ordering quantities.