1. Field of the Invention:
This invention relates to a locking mechanism secured to the bottom end of a tubing string which is to be secured in a hollow bore sump packer located at a position in a subterranean well, such as a substantially horizontal portion of the well which traverses a production formation.
2. Summary of the Prior Art:
In recent years, considerable interest has been expressed in utilizing the economies associated with drilling a subterranean well along a path which traverses the length of the formation, rather than the height or depth of the formation. Such drilling necessarily requires that the initial or entry portion of the subterranean well be substantially vertical and then be curved to produce a deviated portion which traverses the production formation and may lie in a substantially horizontal plane.
The insertion of a tool string through the curved portion of such deviated well requires the application of a substantial downward force accompanied by a rotation of the tubing string and necessarily generates very high frictional resistance to both movements. As a result, when the end of the tubing string reaches a conventional hollow bore sump packer and is inserted therein, an upward pull on the order of 100,000 lbs. must be exerted on the tubing string to insure that the tubing string is anchored to the sump packer.
Conventional locking mechanisms for sump packers normally involves latching elements which are releasable from the sump packer by the exertion of upward forces thereon on the order of 10 or 15 thousand lbs. The frictional forces acting on the tubing string by virtue of passage through the curved portion of the well bore are typically of a magnitude to make detection at the surface of the well of such a small force change extremely difficult if not impossible.
There is, therefore, a definitive need for a latching mechanism for effecting the locking of a tubing string to a sump packer located in a well bore which will withstand, when locked, an upward tensile force on the order of 100,000 lbs., yet may be released from the sump packer through further manipulation of the tubing string.
An additional problem arises in the utilization of conventional latching mechanisms in that the position of the locking elements is generally controlled by a J-slot and pin connection between an outer sleeve element of the latching mechanism and an inner mandrel which is secured to the tubing string. Because rotation of the tubing string is required to effect the insertion of the tubing string through the curved portion of a deviated well bore, conventional shear screws cannot be employed to effect the securement of the J-sleeve and locking pin in a desired position during insertion in the well. There is, therefore, a further problem that has to be solved in providing a J-pin and slot mechanism for effecting the movement of the locking elements to and from a locking position which will not be secured by shear screws or the like during insertion of the locking mechanism through the curved portion of the deviated well so that the exact position of the latching elements relative to the sump packer when such elements reach the sump packer is unknown, yet the reliable functioning of the latching elements solely by manipulation of the tubing string is an essential requirement.
The principal object of this invention is to provide a locking mechanism for a sump packer located in the deviated portion of a subterranean well which will overcome the above mentioned deficiencies of prior art locking mechanisms.