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BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates generally to methods and devices for cleaning and remediating a subsurface safety valve or other downhole tool having a sliding sleeve member.  
         [0003]     2. Description of the Related Art  
         [0004]     Flapper-type valves are often used as safety valves within wells to selectively close off production. The usual flapper valve uses a torsion spring to bias the valve member toward a closed position. During normal operation, however, the flapper member is retained in an open position by an axially moveable flow tube. When the flow tube is moved upwardly within the production tubing, the flapper member is permitted to close under influence of the spring. To reopen the valve, the flow tube is moved downwardly within the production tubing to urge the valve back towards its open position.  
         [0005]     One problem that has traditionally been faced by valves of this type is that scale, dirt, and other debris will often build up within the production tubing during typical production operations. This build up can render the safety valve partially or completely inoperable. The most deleterious build up will be that which occurs on and around the flow tube that is used to open the valve, making the flow tube difficult to physically move upwardly and downwardly. Additionally, the flapper mechanism may be encrusted with scale and other debris making it less likely to fully close when necessary. This means that the valve will be unable to function well in the event of an emergency requiring production flow to be closed off.  
         [0006]     U.S. Pat. No. 6,273,187, entitled “Method and Apparatus for Downhole Safety Valve Remediation,” describes a technique for removing scale and debris build up using explosive charges. The use of explosives, however, carries with it risks of damage to wellbore valve components as well as the potential for a breach of the production tubing string.  
         [0007]     The harmful effects of scale and debris build up can be prevented and reduced by exercising the safety valve, through operation of its components, before the build up has reached a point where the safety valve is no longer fully operational. In the past, this has been accomplished using a gripping tool having mechanical slips that are set against the inside of the flow tube. Once the slips are set, the gripping tool can be pulled upwardly to move the flow tube upwardly or jarred downwardly to move the flow tube downwardly. Unfortunately, tools of this type tend to physically damage the flow tube and other wellbore components, due to the use of the slips.  
         [0008]     The present invention addresses the problems of the prior art.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention provides an improved flow tube exercising tool and method of use. An exemplary flow tube exercising tool is described that is used in conjunction with the hydraulic controller of the safety valve to move the flow tube axially upwardly and downwardly in order to remove build ups of scale and debris from the safety valve and ensure proper operation. The exercising tool provides an engagement portion that underlies the lower end of the safety valve flow tube so that upward movement of the exercising tool will move the flow tube upwardly. Hydraulic fluid is provided to the hydraulic controller to move the flow tube downwardly. Only a single trip of the flow tube exercising tool is necessary to accomplish multiple upward and downward movements of the flow tube. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing.  
         [0011]      FIG. 1  is a side, cross sectional view of an exemplary flow tube exercising tool constructed in accordance with the present invention wherein the exercising tool is being run into production tubing.  
         [0012]      FIG. 2  is a side, cross-sectional view of the exercising tool shown in  FIG. 1  now with the lower engagement portion of the exercising tool engaging the lower end of the safety valve flow tube.  
         [0013]      FIG. 3  is a side, cross-sectional view of the exercising tool shown in  FIGS. 1 and 2  now with the flow tube having been raised to an upper position by the exercising tool.  
         [0014]      FIG. 4  is a side, cross-sectional view of the exercising tool shown in  FIGS. 1-3  now with the tool being disengaged from the safety valve flow tube for removal from the production tubing.  
         [0015]      FIG. 5  is an enlarged view of upper portions of the exercising tool shown in  FIGS. 1-4 .  
         [0016]      FIG. 6  is an enlarged view of upper portions of the exercising tool shown in  FIGS. 1-4  now with the exercising tool engaged with the safety valve.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]      FIGS. 1-4  illustrate a section of a subterranean wellbore  10  that has been lined with steel casing  12  that has been cemented in place by cement layer  14 . The wellbore  10  contains a string of production tubing  16  that defines a production flowbore  18  along its length. A safety valve, generally indicated at  20  is integrated into the production tubing string  16 . The safety valve  20  is a flapper valve, of a type that is well known in the art and described in, for example, U.S. Pat. No. 4,415,036 issued to Carmody. U.S. Pat. No. 4,415,036 is owned by the assignee of the present invention and is incorporated herein by reference. In the safety valve  20 , a flapper valve member (not shown) is biased toward a closed position by a spring (not shown), in the manner well known in the art. The flapper member is opened and retained in an open position by an axially moveable flow tube  22  which, in turn, is actuated by a hydraulic piston-type controller  24 . For clarity, only the flow tube  22  and hydraulic controller  24  portions of the safety valve  20  are depicted in  FIGS. 1-4 .  
         [0018]     At its upper end, the safety valve  20  includes a nipple adapter  26  that is secured by threaded connection  28  to a production tubing string member  30 . The structure of the nipple adapter  26  is best appreciated by further reference to  FIGS. 5 and 6 , which depict portions of it in greater detail. The nipple adapter  26  defines an interior axial flowbore  32  along its length, and an annular dog recess  34  is located within the flowbore  32 . An upwardly directed stop shoulder  35  is also located within the flowbore  32 .  
         [0019]     At its lower end, the nipple adapter  26  is affixed to the hydraulic controller  24 . The hydraulic controller  24  has an annular outer housing that is made up of an upper hydraulic control sub  36  and a lower hydraulic control sub  38 . The lower sub  38  is secured at its lower end to a flapper valve housing  40  that encloses the flapper valve member (not shown). An inner housing portion  42  is secured to the lower sub  38  and a hydraulic fluid piston chamber  44  is defined within the upper and lower control subs  36 ,  38 . An axially moveable piston member  46  is disposed within the chamber  44 . At its lower end, the piston member  46  is secured to the flow tube  22  such that downward axial movement of the piston member  46  within the chamber  44  will result in axial downward movement of the flow tube  22 . One or more hydraulic lines  48  extend from surface (not shown) of the wellbore  10  to the upper hydraulic control sub  36  and interconnect to a fluid passage  50  within the upper sub  36 . The fluid passage  50  interconnects the hydraulic line  48  to the hydraulic fluid piston chamber  44 .  
         [0020]     Also shown in  FIGS. 1-4  is a flow tube exercising tool  52  that is run into the flowbore  18  of the production tubing string  16  at the lower end of a wireline “GS” type running tool  54  of a type known in the art. The flow tube exercising tool  52  includes a tubular mandrel body  55  that is made up of an outer mandrel  56  and a radially inner mandrel  58 . A shear pin  60  releasably interconnects the outer and inner mandrels  56 ,  58  against axial movement with respect to each other. The outer mandrel  56  includes an aperture  62  within which a locking dog  64  is disposed. The inner mandrel  58  has a dog recess  66  (see  FIG. 5 ) which partially houses the dog  64  as well. The dog recess  66  is formed to have an angled cam face  67  at its upper end that faces downwardly and outwardly.  
         [0021]     The outer mandrel  56  is composed of an upper section  68  and a lower section  70  that are releasably affixed to one another by a shear pin  72 . The shear pin  72  is designed to rupture in response to a higher level of force than the shear pin  60 . The lower section  70  also carries a shifting pin  74 . The shifting pin  74  extends radially inwardly through a slot  76  in the inner mandrel  58  and extends further inwardly to project into the flowbore  77  that is defined within the inner mandrel  58 .  
         [0022]     The lower end of outer mandrel  56  is provided with an inwardly-directed tapered surface  78 . The inner mandrel  58  has, at its lower end, a flow tube engagement portion  80  that is shaped and sized to underlie the lower end  82  of the flow tube  22 . In a currently preferred embodiment, the engagement portion  80  is a colleted section  84  with each of the collets  86  presenting a radially outwardly protruding flange  90 . The collets  86  are biased radially outwardly due to shape memory, and, in the initial run-in configuration depicted by  FIG. 1 , are restrained radially inwardly by the lower section  70  of the outer mandrel  56 . The outer radial surface  92  of the outer mandrel  56  presents a downwardly facing stop shoulder  94  (see  FIG. 5 ) that is shaped and sized to abut the stop shoulder  35  of the nipple adapter  26 .  
         [0023]     In operation, the flow tube exercising tool  52  is run down into the flowbore  18  of the production string  16  and lowered until the stop shoulder  94  of the outer mandrel  56  abuts the stop shoulder  35  of the nipple adapter  26 . This is the position shown in  FIG. 1 . Further downward movement of the running tool  54  will cause the shear pin  60  to rupture, thereby permitting the inner mandrel  58  to be moved axially downwardly with respect to the outer mandrel  56 , until the position depicted in  FIG. 2  is reached.  
         [0024]     As the inner mandrel  58  is moved downwardly with respect to the outer mandrel  56 , two things occur. First, the locking dog  64  is set into the dog recess  34  of the nipple adapter  26  in order to securely lock the outer mandrel  56  within the nipple adapter  26 .  FIGS. 5 and 6  illustrate the setting operation. As the inner mandrel  58  moves downwardly (from the position shown in  FIG. 5  to the position shown in  FIG. 6 ), the angled cam face  67  cams the locking dog  64  radially outwardly and into the dog recess  34  in the nipple adapter  26 . The body of the inner mandrel  58  then blocks the locking dog  64  from moving radially inwardly, securing it in place within the dog recess  34 .  
         [0025]     Also, as the inner mandrel  58  reaches its lowermost position, the collets  86  are no longer restrained from outward movement by the lower section  70  of the outer mandrel  56  and will move outwardly so that the flange  90  will underlie the lower end  82  of the flow tube  22 . Once in this position, the flow tube exercising tool  52  may be used, in conjunction with the hydraulic controller  24  to move the flow tube  22  axially upwardly and downwardly in order to remove scale and debris from the safety valve  20  and to ensure that the valve  20  is fully operational. By pulling upwardly on the running tool  54 , the inner mandrel  58  of the exercising tool  52  is moved upwardly with respect to the outer mandrel  56 . Due to the engagement of the flange  90  with the lower end  82  of the flow tube  22 , the flow tube  22  is moved axially upwardly within the valve  20 .  
         [0026]     To return the flow tube  22  to its lowered position, hydraulic fluid is pumped down the hydraulic line  48  to the hydraulic controller  24  and into the hydraulic chamber  44  to cause the piston member  46  and flow tube  22  to move axially downwardly. The flow tube  22  may be manipulated upwardly and downwardly by repeating the above operational steps as many times as desired to ensure proper operation of the valve  20  and the removal of scale and other deposits from its components.  
         [0027]     Normally, the exercising tool  52  may be detached from the flow tube  22  by merely pulling upwardly with sufficient force that the collets  86  are deflected radially inwardly and thus released from the lower end  82  of the flow tube  22 . At that point, the exercising tool  52  is withdrawn from the safety valve  20  and from the tubing string  16 . If, however, the exercising tool  52  cannot be detached in this manner, a release tool  100 , shown in  FIG. 4 , can be run into the interior flowbore  77  of the exercising tool  52  and used to disengage the exercising tool  52  from the valve  20 . The release tool  100  is a tubular sleeve  102  having an axial end portion  104  for contacting the shifting pin  74 . The sleeve  102  is run into the flowbore  77  using a wireline running tool  106 , of a type known in the art. In operation, the end portion  104  of the sleeve  102  contacts the shifting pin  74  and urges it axially downwardly. The shear pin  72  then ruptures, allowing the upper and lower sections  68 ,  70  of the outer mandrel  56  to separate. The lower portion  70  is moved downwardly so that the tapered surface  78  will urge the collets  86  radially inwardly and out of engagement with the lower end  82  of the flow tube  22 . The body of the lower portion  70  essentially acts as a wedge to physically separate the collets  86  from the flow tube  22 . Once disengaged by the release tool  100 , the exercising tool  52  may be removed from the valve  20  by pulling upwardly on the running tool  54 . In so doing, the locking dog  64  will be released from the dog recess  34  when the inner mandrel  58  is raised to the point where the recess  66  is adjacent the locking dog  64 . When this occurs, the dog  64  is cammed radially inwardly toward the recess  66  by sloped surface  110  on the upper side of the dog recess  34 .  
         [0028]     The flow tube  22  may be moved axially upwardly and downwardly in an alternating manner as described above as necessary to remove scale and other debris and ensure proper operation of the safety valve  20 . Movement of the flow tube  22  may be exercised in this manner using only a single trip of the exercising tool  52  into the production tubing  16 . However, the exercising tool  52  may also be run into the production tubing  16  on several separate occasions during the life of the wellbore to ensure continued proper operation of the safety valve  20  throughout.  
         [0029]     Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.

Summary:
A flow tube exercising tool and method for use are described for actuating the flow tube of a downhole safety valve in order to remove build ups of scale and debris from the safety valve and ensure proper operation. The exercising tool provides an engagement portion that underlies the lower end of the safety valve flow tube so that upward movement of the exercising tool will move the flow tube upwardly. Hydraulic fluid is then provided to the safety valve hydraulic controller to move the flow tube downwardly. Only a single trip of the flow tube exercising tool is necessary to accomplish multiple upward and downward movements of the flow tube.