Abstract: A locking apparatus for positioning a well tool within a subterranean well bore and comprising a primary locking member attached to the well tool; a nipple incorporable in a subterranean well conduit; and running and retrieving tools for positioning the lock member is disclosed. The lock has a no-go shoulder for initially positioning the lock adjacent the nipple and radially expandable locking dogs for carrying both upwardly and downwardly directed forces upon full expansion thereof after the no-go shoulder has been disengaged. At least two interlocking members disengagable only by separate manipulations maintain the locking dogs in a radially expanded fully engaged position. A retrieving tool having a rotational alignment means to position the tool relative to the lock is used to separately manipulate the interlocking members and to pull the disengaged lock from the well.

Abstract: The disclosure provides a method and apparatus for effecting the locking of a well tool in any selected one of a plurality of identical nipples provided in spaced relationship along a well tubing string. Each nipple is provided with an annular recess to receive expandable locking dogs carried by the locking mechanism and an upwardly facing no-go shoulder which is of no lesser diameter than the bore of the tubular string. The locking mechanism is shearably mounted on a running tool and incorporates an expansible C-ring which has a downwardly facing shoulder engagable, when expanded, with the no-go shoulder of the selected locking nipple. The expansible C-ring is held in a retracted position by a collet having spring arms which pass freely downwardly through any or all of the nipples but, when moved upwardly through a selected nipple, engage a surface on the nipple and pull the collet out of its retaining position with respect to the expansible C-ring.