دیکشنری تخصصی مهندسی نفت - نسخه آنلاین

n: a device used to enlarge the size of an existing borehole. It has teeth arranged on its outside circumference to cut the formation as it rotates.

n: a special drilling tool that can enlarge an existing hole to the required diameter.

a larger device (usually of a fixed diameter) that enlarges the wellbore to a diameter equal to or less than the upper casing drift). Compare to an under-reamer or watermelon mill or string mill.