Over the past decade the use of expendable concentric under reamers or “whole openers” concentric under reamers or “whole opners” in deep water drilling has become widespread. An estimated 75% of the salt/sub salt sections in the Go now use under reamers. there are various reasons to Enlarge a hole, including enhancing equivalent circulating density. to reduce cementing pressure and to counter salt ceep so causing will reach bottom. Under reamers are especially important in deep water wells that require numerous casing strings.