METHOD AND APPARATUS FOR ACCURATE MILLING OF WINDOWS IN WELLCASINGS

摘要

A method and apparatus for predictable downhole milling of a casing window having predetermined location, orientation, dimension and contour geometry. An elongate substantially rigid milling shaft (62) has at least one casing wind ow milling element (88, 90) in fixed relation therewith and has a pilot mill (3 4) in articulated and rotary driven connection with the milling shaft (62). The milling shaft (62) is in articulated and rotary driven connection with a rotary drive mechanism. The articulated connection (56, 58) of the pilot mil l (34) and milling shaft (62) may incorporate an articulation control system t o permit the pilot mill (34) to be maintained substantially coaxial with the milling shaft (62) so that its trajectory at a predetermined stage of window milling can be controlled by the milling shaft (62) when positive guiding by a deflecting tool (12) can no longer be ensured.