The present invention relates to wellbore tools and more particularly to an apparatus for retrieval of metal objects, such as cuttings and other foreign objects that accumulate in the process of perforating or milling over bridge plugs and other down hole obstructions from a wellbore.
Various types of bridge plugs are conventionally used in the oil and gas industry. These bridge plugs are installed in the annulus and are often covered in cement. Removal of such plugs can sometimes pose a problem for the industry. A rotary bit drills the cement and plugs out, while some of the cuttings of the plugs are carried out to the surface by a liquid circulated down hole.
Sometimes, a production packer needs to be removed together with the metal pipe that it surrounds. In those cases, milling tools with gravity fed boot baskets are used for retrieving pieces of metal from the wellbore. After retrieval of the production packer, it may become necessary to run a conventional fishing magnet to retrieve additional junk and cuttings.
A conventional fishing magnet is mounted inside a housing that is lowered into a wellbore. It is limited in the ability to retrieve cuttings in that its magnetization is restricted to the extreme bottom surface of the magnet. The fact that circulating fluids lift the cuttings away from the bottom surface of the magnet renders that conventional fishing magnet useless in this situation.
Often times, a boot basket is used for collecting cuttings that did not attach themselves to the conventional magnet. A boot basket has small openings for catching these particles. Consequently, many large size pieces or very small pieces suspended in the fluid flow are not trapped in the basket and remain in the wellbore.
The present invention contemplates elimination of drawbacks associated with the prior art and provision of a wellbore apparatus for removal of metal objects, such as cuttings, and other foreign particles that provides for the use of sets of magnets spaced longitudinally along the tool body.
It is, therefore, an object of the present invention to provide an apparatus for retrieval of metal cuttings and other foreign objects from a wellbore.
It is another object of the present invention to provide a packer-milling tool with magnets set in a spaced relationship longitudinally along the tool body to increase xe2x80x9ccatchingxe2x80x9d capacity of the tool.
These and other objects of the invention are achieved through a provision of an apparatus for removal of metal cuttings and other foreign objects from a wellbore that uses at least two magnet assemblies vertically spaced from each other and mounted on the body of the tool. Each magnet assembly is comprised of a plurality of magnets encircling the body of the tool and covering a surface area greater than one half of the tool body.
One of the embodiments of the invention provides for arcuate in cross section magnet members that are detachably secured on the tool body. The second embodiment provides for trapezoidal in cross section magnet members that extend longitudinally in parallel relationship to a central axis of the tool body. The tool of the second embodiment further provides for magnet protectors mounted adjacent to each magnet member. Each magnet protector has a triangular cross section and has a slanted surface that is angled in the direction of rotation.
The space between each magnet and the next adjacent magnet protector forms a xe2x80x9ctrapxe2x80x9d that receives and retains metal particles pushed away by the leading surface of the adjacent magnet member. Consequently, the capability of the tool to retain cuttings for subsequent retrieval to the surface is significantly increased in comparison with conventional magnet tools.