Abstract: A system of cleaning a portion of the casing prior to a plugging operation may include a centralizer, a first radially extendable cutting tool, a second radially extendable cutting tool, a preliminary extendable cleaning tool, and a fluid jet cleaning tool. In a preferred embodiment a centralizer, a radially extendable cutting tool, and a fluid jet cleaning tool are run into a wellbore where the radially extendable cutting tool cut the window through the inner production tubular and the fluid jet cleaning tool removes the remaining's cement and other debris allowing a plug to be placed within the window. In another embodiment a centralizer and a first extendable cutting tool may be run into the well where a small window is cut and then the centralizer first extendable cutting tool are removed from the wellbore. A centralizer, a second extendable cutting tool, and a fluid jet cleaning tool a run into the wellbore.

Abstract: A mill assembly having a milling head which is releasable from the mill body, such as by shifting a ball clutch mechanism. The ball clutch mechanism can be shifted 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.

Abstract: 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.

Abstract: 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.