Releasable mill

摘要

A mill assembly having a milling head which is releasable from the mill body, such as by shearing a shear pin. The release mechanism can be released by dropping a pumpable plug through the work string to block fluid flow through the releasable milling head, or by increasing fluid flow through a constriction in the releasable milling head to increase the back pressure above the milling head. A check valve in the milling head can prevent uphole flow through the work string in the event of a pressure excursion. A fishing neck can be attached to the milling head.