Abstract:
A device for removing junk from a well by attaching to a tubing string a mill body with a removable milling core and lowering the assembly into a well. A movable collet and check valve are located in the milling core. The milling core can be separated from the mill body by dropping a ball bearing into the tubing and then feeding water under pressure into the tubing behind the ball bearing.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Provisional Application No. 61076089 filed on 26 Jun. 2008, the disclosure of which is incorporated herein in its entirety by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a downhole junk removal tool for use in removing junk from a well bore. 
         [0004]    2. Description of Related Art 
         [0005]    Pump off junk mills are used to remove various downhole obstructions, commonly referred to in the petroleum recovery industry as “junk.” Junk mills are frequently used to clean out various metallic and non-metallic obstructions that are in a downhole. Junk is anything that is not supposed to be in the downhole and can include various objects that are accidentally dropped downhole from the surface such as hand tools, wrenches, or parts that have broken off during drilling such as drill bit teeth, nozzles, etc., or accumulated cement or other sediment left behind from a previous downhole operation. A downhole mill is typically located at an end of a work string so that the cutting head of the mill can be rotated and axially loaded against the material that is to be cut. 
         [0006]    A “mill” is a tool that grinds metal downhole. A mill is normally used to remove junk in the downhole or to grind away all or part of a casing string. In the case of junk, the metal must be broken into smaller pieces to facilitate its removal from the wellbore so that the drilling operation can continue. Virtually all mills utilize tungsten carbide cutting surfaces. 
         [0007]    A typical downhole mill includes rotary cutters with hardened cutting surfaces that cut or grind material such as metal, plastic, etc. In contrast, a downhole drill bit is typically used to cut rock or downhole formation. 
         [0008]    Mills, are run down a borehole to cut man-made obstructions referred to as junk, so that a drilling operation can continue. A further category of junk are larger objects. These may include portions of tools which have been discarded or been broken within the well bore, or large sections of tubes which have been cut away when portions of a casing have been milled or drilled. 
         [0009]    Apparatus within a well bore designed to collect junk primarily fall into two categories that are dependent upon the location of the tool on a work string. The first category relates to apparatus mounted at the bottom of the work string. This apparatus collects all fluids and materials within the well bore as fluids are circulated up the well bore or as the tool is run into the well bore. Such tools are typically referred to as junk catchers. This tool has a collection of petals arranged at the distal end of the work string. As the tool is run into the well, the petals are forced outward to the walls of the well bore where they act to siphon all material through a single large port on the longitudinal axis of the tool. When the tool is pulled from the well the petals close thereby catching large debris and pulling it from the well. 
         [0010]    A significant disadvantage of this tool is that it must be positioned at the end of a work string and thus is typically used on a single run. To operate a dedicated run merely for the purposes of clearing junk is both time-consuming and expensive. 
         [0011]    The second category of junk catchers can be mounted at any position on a work string to allow the tool to be run at the same time as other tools. The tool has a wiper or scraper blade arranged to prevent the fluid including the junk to pass up the annulus between the tool and the well bore wall. The fluid including the junk is forced into a port and through a passage in the tool around the wiper. A filter and a trap are positioned within the passage to catch the junk, which is too large to pass through the filter. 
         [0012]    Such tools have an input port that is sized to ensure that a significant flow velocity is maintained to circulate the fluid through the tool. These tools generally include a by-pass means which rupture to allow the fluid to escape when the filter has been clogged with large debris. Thus, when large debris is present the tool cannot function correctly and, in fact, generally shuts down into a mode that allows the fluid including the junk to by-pass the tool. Additionally, junk tends to ‘ball-up’ at the scrapers or wipers as the larger pieces of junk are swept away from the inlet port up the annulus to become jammed or located around the wiper blades. 
       SUMMARY OF THE INVENTION 
       [0013]    A device for removing junk from a well by attaching the tubing string to the mill body and lowering the assembly into a well. A movable collet located inside the core couples the mill body to the milling core and a check valve is located inside the core. The milling core is controllably separated from the mill body by dropping a ball bearing into the tubing and then feeding water under pressure into the tubing on top of the ball bearing. 
         [0014]    The foregoing has outlined, rather broadly, the preferred feature of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention and that such other structures do not depart from the spirit and scope of the invention in its broadest form. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claim, and the accompanying drawings. 
           [0016]      FIG. 1  is an exploded diagram showing the pump off junk mill components; and 
           [0017]      FIG. 2  is a flow diagram of the process of using the pump off junk mill. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    This invention relates to a pump off junk mill that does not have to be removed from a downhole. The tungsten carbide mill has a full opening through the center with a back pressure valve and core which is connected to a string of tubing that latches into the system. A check valve assembly and the mill core is removed from the tubing by dropping a ball bearing down the tubing and then pumping fluid. A collet located in the milling core is urged to shift, allowing the milling core and its components to be released and drop to the bottom leaving the mill body in tact with the tubing string. 
         [0019]    Thus, the mill body can be used for future cleanouts without removing it from the tubing string. 
         [0020]    Existing mills must be pumped off entirely which leaves the mill as “junk” in the well in addition to junk hanging up in perforations, all of which can result in blocking the well. With existing mills, the premature releasing of the mill prior to the completion of the drilling process can result in increased cost and added time to the drilling process. Current pump out cores use a one piece mill design that utilizes shear/set screws that will shear off during deployment in the well. When the shear/set screws shear, the mill separates from the tubing and drops down to the bottom of a well to become junk which cannot be used in the future. 
         [0021]    The core here disclosed which is attached to a mill can be retrieved and a new core with valve assembly can be added resulting in a unit that can be used again. It is not left in the well as junk which may have to be removed at some future time. 
         [0022]    Existing cores use shear/set pins which can shear and allow a mill to be released and drop down to the bottom of the well. Retrieving the dropped mill can be time consuming and costly. The core here disclosed has a collet that shifts, it does not shear, which allows the mill core to be released and subsequently retrieved when desired. 
         [0023]    Referring to  FIG. 1  there is shown an exploded view of the new improved milling core  10 . A check valve assembly  12  is located within a milling core  14  that is located within a mill body  16 . The check valve assembly comprises, as is shown in  FIG. 1 , a collet  18  that is inserted into an upper housing  20  through an end  22  of the upper housing  20 . The upper housing  20  has openings that receive ball bearings  24 . A ball seat  26  is coupled to end  28  of the upper housing  20 , and receives seal ball  28  that is held against the ball seat by spring  30 . O rings are located between the various parts to provide fluid tight seals. 
         [0024]    An assembly instruction pamphlet for assembling the various parts of  FIG. 1  contains the following information. 
         [0025]    Assemble the milling core and the check vale assembly, making certain that all the proper O rings are installed. 
         [0026]    Put the collet in through the top of the check valve assembly and tap in with an assembly tool 
         [0027]    Insert the spiral lock ring into the gland located inside the upper housing. 
         [0028]    Lower the mill body over the entire check valve assembly and milling core. 
         [0029]    Using a “Tap-in tool”, strike the upper end gently until the collet bottoms out inside the upper housing. This will be about one inch of travel. 
         [0030]    Insert the four ball bearings through holes in the upper housing. Place a small amount of grease on the ball bearings to hold in place, if necessary. 
         [0031]    Using an insertion/retraction tool, screw the tool into the collet (located inside the CVA assembly) which will shoulder at the right depth. Put base plate on the shoulder of the assembly and screw on the nut provided. 
         [0032]    Turn the nut clockwise until the collet is pulled up against the spiral lock ring. This is exactly one inch travel. 
         [0033]    The assembly is now ready for shipment. 
         [0034]    Prior art mills have shear/set pins which can be damaged and can result in the mill being released into the well. This results in a fishing job and additional cost. This can not happen with this invention. 
         [0035]    Referring to  FIG. 2 , the process begins by placing a junk mill on the bottom of a tubing string and placing the junk mill in a well. Block  50 . Then the tubing is hooked up to a Kelly and fluid water or drilling mud is pumped down the tubing, block  52 . The tubing is lowered until the junk in the well is contacted, block  54 . Now 2 barrels per minute of water or drilling mud are pumped through the tubing as the pipe is rotated to the right with about 2000 pounds of weight on the junk mill, block  56 . The particles are washed to the surface, block  58 . After all of the particles are removed, the tubing is pulled to a desired depth for producing gas, block  60 . A ball bearing having a diameter of 15/16 is dropped into the tubing, block  62 . Upon arrival of the ball bearing at the junk mill, water pressure of between 450 psi and 550 psi where a preferable pressure of approximately 500 psi is applied to the tubing, block  64 . The pressure shifts the collet inside the junk mill detaching the 2 inch core of the mill, block  66 . The core is released to the bottom of the well allowing gas or oil to flow up the tubing back to the production unit, block  68 . 
         [0036]    The method eliminates the removal of the tubing string under pressure and subsequent reentry, and leaves a useful cleanout tool in the well for future flow problems. 
         [0037]    While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that various omissions and substitutions and changes of the form and details of the apparatus illustrated and in the operation may be done by those skilled in the art, without departing from the spirit of the invention.