Patent ID: 8905126

Claim:
A drift sub equipped to be capable of cleaning at least part of the interior surface of a casing in a subterranean well prior to the insertion therein of completion hardware and/or accessories, the drift sub comprising: a tubular housing having an upper end, a lower end and a bore extending therebetween, said housing being deployable into and moveable within the casing; a plurality of mill blades supported on said housing and arranged in at least one row around the outer circumference of said housing, each said mill blade being movable between at least one retracted position and at least one extended position relative to the housing, said mill blades in said extended position extending radially outwardly beyond the outer diameter of said housing and capable of contacting the interior surface of the casing, and said mill blades in said retracted position being unable to contact the interior surface of the casing, wherein said mill blades are initially positioned in said retracted position upon deployment of said housing into the casing; an inner sleeve disposed within said bore of said housing and biasingly engaging each said mill blade, said inner sleeve being configured to be selectively movable axially relative to said housing only in the direction of said lower end thereof at least from a first position to a second position and therefrom to a third position, said inner sleeve in said first and third positions biasing said mill blades in said retracted position and said inner sleeve in said second position biasing said mill blades in said extended position; and an outer sleeve disposed within said bore radially outwardly relative to said inner sleeve and being releasably engaged therewith, said outer sleeve being configured to be selectively moveable axially relative to the housing only in the direction of said lower end thereof at least from a first position to a second position, wherein movement of said outer sleeve from its said first position to its said second position causes said inner sleeve to move from its said first position to its said second position, wherein said inner and outer sleeves are configured to be positioned in said respective first positions upon deployment of said housing into the casing and, thereafter, movement of said outer sleeve from its said first position to its said second position moves said inner sleeve from its said first position to its said second position, causing said mill blades to move into said extended position, and movement thereafter of said inner sleeve from its said second position to its said third position causes said mill blades to move into said retracted position, and whereby said inner sleeve in its third said position is unable to move back to its first or second said positions, securing said mill blades in said retracted position.