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BACKGROUND 
       [0001]    In the downhole drilling and completion industry flapper valves have been used for an extended period of time. Such devices are useful whenever it is necessary to cause a fluid to move into the downhole environment from a remote location such as a surface location. Flapper valves come in a number of forms but not uncommonly are configured as tubing retrievable injection valves (TRIV), for example. Such valves often comprise a flapper that articulates and a flow tube that translates through a position occupied by the flapper when closed, thereby maintaining the flapper in an open position throughout the injection cycle. The open position is so maintained by the flow tube structurally pushing the flapper out of the way (causing rotation about its pivot) when the flapper valve is in the open position. While such flapper valves work well for their intended purposes, improvement is always desirable whether that improvement be in performance, cost reduction or both. 
       SUMMARY 
       [0002]    A flapper valve with magnetic field hold open arrangement including a housing; a flapper pivotally mounted to the housing; and a magnet housing slidably mounted to the housing such that a magnetic field generating configuration of the magnet housing is movable between a position where it is capable of holding the flapper in an open position and where it is incapable of holding the flapper in an open position. 
         [0003]    A method for holding open a flapper of a flapper valve including pumping an injection fluid through the valve with magnetic field hold open arrangement including a housing; a flapper pivotally mounted to the housing; and a magnet housing slidably mounted to the housing such that a magnetic field generating configuration of the magnet housing is movable between a position where it is capable of holding the flapper in an open position and where it is incapable of holding the flapper in an open position; fording the flapper to an open position; coupling the magnet housing by fluid friction to the flowing injection fluid; urging the magnet housing downstream whereby the magnetic field generating component is in the position to hold the flapper in the open position; and magnetically holding the flapper in the open position. 
         [0004]    A flapper valve with hold open arrangement including a flapper movable between an open condition and a closed condition; and a magnetic field generating component movable relative to the flapper to be in a position where the component is capable of magnetically holding the flapper in the open condition and a position where the component is incapable of holding the flapper in the open condition. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
           [0006]      FIG. 1  is a schematic view of a flapper valve as disclosed herein in a closed position; 
           [0007]      FIG. 2  is a schematic view of the valve of  FIG. 1  in an open position. 
           [0008]      FIG. 3  is a schematic view of a portion of an alternate embodiment of the flapper valve disclosed herein, the portion circumscribed by line  3 - 3  in  FIG. 2 . 
           [0009]      FIG. 4  is an alternate embodiment of a flapper valve in a closed position. 
           [0010]      FIG. 5  is an alternate embodiment of a flapper valve in an opened position. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Referring to  FIG. 1 , valve  10  such as a flapper valve includes a relatively short flow tube  12  disposed in operable communication with a relatively short housing  14 . The flapper valve  10  further includes a flapper  16  articulated to the housing  14  at a pivot point  18 . A seal  20  is disposed at the housing  14  and positioned for interaction with the flapper  16  when the flapper valve  10  is in the closed position. More specifically, the seal  20  ensures that the flapper  16  when closed will form a fluid tight interface with the housing  14 . Such seals are common and tend to be relatively soft. This makes them vulnerable to flow cutting and hence they require protection. Protection in the illustrated configuration is provided by a flow tube that need be only long enough to extend past the seal  20  when the flapper  16  is open. This is illustrated in  FIG. 2 . Further, one of ordinary skill in the art will recognize that as illustrated, the flow tube would not function to open the flapper  16  as is the case in many prior art valves but rather stops short of interacting physically with the flapper  16 . In this configuration, it is the flow of injection fluid that opens and maintains the flapper  16  in the open position. The flow tube in this configuration then has only to protect the seal  20 , which it does in the position illustrated in  FIG. 2 . It is noted that it is possible to apply the concepts herein to a valve with a longer flow tube that also has function to open the flapper  16  but such function is not necessary to the teaching herein. In either case, an extension spring  22  in operable communication with the flow tube  12  and the housing  14  will automatically move the flow tube  12  to the operational position when the flapper  16  is opened, that opening being due solely to flow or to flow in combination with another opening impetus. 
         [0012]    The flapper  16  itself comprises an erosion resistance that is either surface concentrated such as in the form of a coating or a surface layer or may be erosion resistant for a greater percentage of the flapper  16 , including but not limited to the entire flapper being composed of erosion resistant material. This configuration allows the use of the valve  10  with high injection flow rates without a flow tube  12  being long enough to cover the flapper  16 . 
         [0013]    Because the flapper is exposed to flow during use of the valve  10  due to a short flow tube, fluid dynamics considerations are of importance when they are traditionally irrelevant to the flapper. The fluid flowing past and in contact with the flapper  16  causes turbulence behind the flapper  16  adjacent an inside surface  24  of a tubular  26  in which the valve  10  is installed. The turbulence can cause the flapper to move into the flow stream and not stay against the surface  24 . This is a hindrance to injection and hence is to be avoided. The problem is exacerbated by higher injection rates. In order to address this issue the inventor hereof has determined that the effect of turbulence with respect to its ability to move the flapper into the injection flow can be minimized by reducing the fluid volume between a surface  28  of the flapper  16  and the surface  24 . It is to be noted that the surface  28  may be of the flapper itself or may be of a material attached to the flapper. In one embodiment, the surface  28  is formed by providing a conformable material  30  attached to the flapper  16 . The conformable material  30  will assume the shape of the inside surface  24  upon contact therewith and prevent any significant turbulent fluid from urging the flapper  16  away from the surface  24  during injection. This embodiment allows for irregularities in the surface  24  to be accounted for without knowing what those irregularities might be. More specifically, the tubing string in which the valve  10  is installed may have experienced flow cutting or erosion or may have become deformed during run in and resultingly does not necessarily present a cylindrical geometry at the surface  24  for a preconceived surface  28  to geometrically mate with. In such situation a conformable material  30  provides a wider range of functional success in reducing any potential volumes within which turbulent fluids might otherwise act. Conformable materials include but are not limited to rubber, nitrile, foams (including shape memory foam), etc. In other embodiments, the material may be a nonconformable material attached to the flapper or may be the flapper itself. In such cases, the material may geometrically mate well with the inside surface  24  and perform substantially as does the conformable material or may geometrically mate less well with the surface  24  but in any event, the material  30  will be formed to substantially geometrically mate with the surface  24  and accordingly will substantially displace turbulent fluid from the volume defined between the surface  28  and the surface  24 . Due to the reduction in turbulent fluid in this location, impetus on the flapper  16  to move into the flow path of the injection fluid is reduced or eliminated. 
         [0014]    Still referring to  FIGS. 1 and 2 , the torsion spring  19  operates to oppose the force of flowing injection fluid but without sufficient energy to overcome the force of the flowing fluid. The flapper  16  then will be opened by the flowing fluid but will close automatically upon cessation of flow of the injection fluid. In one embodiment, the torsion spring is configured with a greater spring force than the extension spring  22  such that the flow tube may be pushed back to its unactuated position by the flapper  16  through the impetus of the torsion spring  18 . 
         [0015]    In addition to the foregoing, and referring to  FIG. 3 , the flapper may further include a magnetic component  32  that is attractive to the tubing  26  or to another magnetic component  34  disposed in the tubing  26 . The magnet(s) either singly or in combination act to maintain the flapper  16  in contact with the surface  24  thereby reducing any available volume into which fluid may flow which consequently reduces any possible impetus for the flapper  16  to move into the injection flow. In addition, because of the attractive force of the magnets, it is in one embodiment, not necessary to have the surface  28  or material  30  of  FIGS. 1 and 2 .  FIGS. 4 and 5  illustrate such an embodiment. With respect to releasing the magnetic attraction of any of the embodiments herein that include magnetic field generating components whether of opposing poles or only one sided and attractive to a ferrous material, a sliding action will be used. For an understanding of such an action and one embodiment of a configuration capable of producing the sliding action, see  FIGS. 4 and 5  and the description thereof hereinbelow. 
         [0016]    Referring to  FIGS. 4 and 5  simultaneously, an embodiment of a flapper valve  100  that ensures the flapper stays in the open position regardless of turbulence as illustrated. Illustrated is a housing  101  having a magnet housing  102  disposed therein. The magnet housing is axially movable within the housing  101  and is fluid sealed thereto by one or more seal  104 . The magnet housing  102  supports a magnetic field generating component  106  that comprises a permanent magnet or an electromagnet. The magnet housing  102  is biased by a compression spring  108  that may be a coil spring as illustrated or any other type of spring that provides resilience in compression. The spring  108  is maintained in position by a shoulder  110  in the housing  101  and a flapper sub  112  that bounds the annular space in which the spring  108  is located. The flapper sub  112  is a non movable component that is at least partially composed of a nonmagnetic material, the part being where a magnetic field would need to pass through the sub  112 . This area is labeled  115 . The sub  112  is anchored by suitable means  114  at recess  116  in housing  101 . The suitable means  114  may be one or more fasteners such as threaded fasteners, welding, adhesive, press fit, etc. at an end of flapper sub  112  opposite the means  114  is a pivot  118  and torsion spring  120  that together allow pivotal movement of a flapper  122  and a bias of the flapper  122  to its closed position (illustrated in  FIG. 4 ). Adjacent a portion of the flapper  112  is a flapper seat  124  and a seal  126  thereat. Seat  124  may be attached to flapper sub  112  at and by, for example, thread  128 . A flow tube  130  is positioned radially inwardly of the seat  124  and is moveable therein. The flow tube is connected to a tension spring  132  that is also connected to the flapper seat  124 . The tension spring  132  tends to bias the flow tube toward the flapper  122  such that when the flapper  122  is in an open position the flow tube will protect the seal  126  from erosion due to fluid flow. The flow tube  130  need merely extend a small distance past the seal to provide this protection. It is to be understood that the tension spring  132  is sufficient in spring rate only to move the flow tube 130  to the protective position but is insufficient to prevent closure of the flapper  122  based upon input from the torsion spring  120 . This configuration ensures that the flapper  122  will close properly when it is supposed to without the flow tube interfering with the closure. Finally, the flapper  122  is provided with a magnetic field generating component  136 , which in one embodiment comprises a permanent magnet but may be configured as an electromagnet. In one embodiment the exposed surface of the component  136  will be of an opposing magnetic pole to the exposed surface of the component  106 . It is inconsequential which one of the two is north or south pole oriented. 
         [0017]    In operation, a fluid  138  is applied in the direction of flow arrow  140  toward the flapper valve  100 . The fluid  138  forces the flapper to swing open (position depicted in  FIG. 5 ), and simultaneously through fluid drag, moves the magnet housing  102  in the same direction as fluid movement. This action causes the magnetic field generating component  106  to move along with the magnet housing  102  to a position where the arcuate movement of magnetic field generating component  136  will be in register therewith, the movement of component  136  being dependent upon the pivoting movement of flapper  122 . Because the two components  106  and  136  are aligned and positioned in proximity to one another as well as being oppositely poled, the flapper is magnetically held in the open position and hence out of the flow of fluid  138 . By design the spring force of the torsion spring  120  is insufficient to overcome the magnetic attraction between components  106  and  136  and therefore is of no consequence with respect to maintaining the flapper  122  in the open position. As one of skill in the art will recognize, the flapper of a valve of this type must close when injection is stopped. This action is also unimpeded because as soon as the fluid drag on the magnet housing  102  is relieved, secondary to a pause in the flow of fluid  138 , the compression spring  108  will elongate and force the magnet housing  102  to move to the closed position of  FIG. 4 . This will cause the magnetic field generating component  106  to slide away from the magnetic field generating component  136  thereby substantially reducing the attractive force therebetween. The flapper is hence free to close under the impetus of the torsion spring  120 . 
         [0018]    In other embodiments, it is noted that the magnetic field generating components need not be on both sides of the resulting attractive interface but rather one could simply be a magnetically responsive material such as a ferrous metal. A reduced attractive force would result but if the component used has a sufficiently potent field, it would still function as noted above. Sliding action would still be used to break the interface wither by moving a nonmagnetic material into proximity with the components while the magnetically responsive material is slidingly moved away or a configuration where a sliding movement would simply position the field generating component farther away from a responsive material such as by sliding one of the structural features described in a direction that allows a recess to be aligned with the filed generating component. In such an embodiment the recess would position a responsive material far enough away from the field generating component to reduce the attractive force to a magnitude less than a closing force supplied by the torsion spring. 
         [0019]    While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.

Summary:
A flapper valve with magnetic field hold open arrangement including a housing; a flapper pivotally mounted to the housing; and a magnet housing slidably mounted to the housing such that a magnetic field generating configuration of the magnet housing is movable between a position where it is capable of holding the flapper in an open position and where it is incapable of holding the flapper in an open position. A method for holding open a flapper of a flapper valve.