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CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Patent Application Ser. No. 60/560,152 filed Apr. 7, 2004. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates generally to the design of flapper valves. 
   2. Description of the Related Art 
   A flapper valve is a plate-like member that is pivotally affixed to one side of the tubing string and may be rotated 90 degrees between an open position and a closed position. A spring member typically biases the flapper element toward its closed position. The flapper element is typically opened using hydraulic fluid pressure. 
   Flapper valves have a variety of downhole uses, including safety valves. In addition, flapper valves can be incorporated into fluid loss control valves and wellbore isolation valves. In such instances, the flapper valve is installed in an inverted position so that the flapper element opens by being pivoted upwardly (toward the opening of the well). 
   At times, it is necessary to reopen a flapper valve after it has been closed. However, if the hydraulic system for opening the flapper valve should fail, there is a lack of reliable backup means for opening the flapper element. In prior art techniques, a pipe or other tubular member is brought into engagement with the flapper element to push it off of its valve seat and rotate the valve member to its open position. An example of this is described in U.S. Pat. No. 6,705,593 issued to Deaton. However, this opening mechanism is not useful where the flapper element opens upwardly (i.e. toward the surface of the wellbore). In that case, urging a tubular member against the valve member would only force the valve assembly closed. 
   The present invention addresses the problems of the prior art. 
   SUMMARY OF THE INVENTION 
   The invention provides methods and devices for operation of a flapper valve. An exemplary valve assembly is described with a flapper element and a valve opening assembly that will mechanically open the flapper element. The valve opening assembly is particularly valuable where the flapper element fails to open in response to normal hydraulic opening techniques. In a described embodiment, the valve opening assembly includes a valve opening sleeve having a generally hemispherical cross-section and an opening portion that presents a pair of opening shoulders. The opening shoulders engage lugs on the flapper element so that movement of the opening sleeve will urge the flapper element to an open position. The valve assembly may be run into the wellbore with the flapper element in the open position, rather than having to be closed, as with a number of conventional valve assemblies. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein: 
       FIG. 1  is an isometric view of an exemplary flapper valve assembly constructed in accordance with the present invention in a run-in position. 
       FIG. 1   a  is a detail drawing depicting configuration of a J-slot and lug assembly in the valve assembly shown in  FIG. 1 . 
       FIG. 2  is an isometric view of the valve assembly shown in  FIG. 1 , now with the flapper element closed. 
       FIG. 2   a  is a detail drawing showing configuration of the J-slot and lug assembly. 
       FIG. 3  is an isometric view of the valve assembly shown in  FIGS. 1 and 2 , now with the upper valve seat engaged with the flapper element. 
       FIG. 3   a  is a detail depicting configuration of the J-slot and lug assembly in the valve assembly. 
       FIG. 4  is an isometric view of the valve assembly shown in  FIGS. 1-3 , now with the upper valve seat lifted off of the flapper element. 
       FIG. 4   a  is a detail drawing showing configuration of the J-slot and lug assembly. 
       FIG. 5  is an isometric view of the valve assembly shown in  FIG. 1 , now with the flapper element open. 
       FIG. 5   a  is a detail drawing showing configuration of the J-slot and lug assembly. 
       FIG. 6  is an isometric view of the valve assembly shown in  FIG. 1 , now with the flapper element being mechanically lifted off of the lower valve seat. 
       FIG. 6   a  is a detail drawing showing configuration of the J-slot and lug assembly. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 ,  1   a  through  6 ,  6   a  illustrate the construction and operation of an exemplary flapper valve assembly  10  in accordance with the present invention. The flapper valve assembly  10  is primarily useful as a fluid loss control valve, which can be run into a wellbore with a flapper element in either the open position or in the closed position. Secondarily, the flapper valve assembly  10  may be employed as an isolation valve, wherein the valve assembly is run with the flapper element in a closed position. Apart from the “valve opening assembly,” and “opening sleeve,” components, which are described below, the structure and function of the valve assembly  10  is the largely the same as that of the “Full Bore Isolation Valve,” which is marketed commercially by Baker Oil Tools of Houston, Tex. The “Full Bore Isolation Valve” is fully described, for example, in Baker Oil Tools&#39; Packer Systems Technical Unit No. 10212 (Oct. 28, 2004), which is incorporated herein by reference. This variety of valve is designed to provide isolation within a tubing string, holding pressure from both above and below when closed. Because the general details of construction and operation of this type of valve assembly are known to those of skill in the art, and otherwise available, they are not described in great detail herein. 
   The valve assembly  10  is typically incorporated into a production tubing string (not shown) of a type known in the art and disposed into a wellbore in a manner that is well understood by those of skill in the art. An axial flowbore  11  is defined along the length of the valve assembly  10 . Those of skill in the art will recognize that a number of exterior housing sleeves are associated with the Full Bore Isolation Valve that are not depicted in  FIGS. 1-6 , in order to provide clarity to the drawings. The uphole direction during typical downhole operation is illustrated by arrow  12  in  FIG. 1 . Further, the valve assembly is shown in  FIG. 1  to be in a “running-in” position, with the valve assembly  10  open to permit the passage of fluids and tubing or tools therethrough. 
   The flapper valve assembly  10  includes a cylindrical central valve mandrel  14 . The outer surface of the central valve mandrel  14  is inscribed with a lug pathway  16  of the type normally referred to as a “J-slot.” The design of the lug pathway  16  is best seen in  FIG. 1   a  to have a short leg portion  18  and a long leg portion  20  that are joined at an angular point  22 . 
   The lower portion of the mandrel  14  is shown to reveal flapper element  24  that is secured by hinged attachment  26  to a hinge sleeve  27 . The flapper element  24  is a curved plate having a first axial side  24   a  and a second axial side  24   b . In  FIG. 1 , the flapper element  24  is in an open position. It is noted that the flapper element  24  has two side lugs  28  (one shown) that project outwardly from opposite edge surfaces of the flapper element  24 . The central mandrel  14 , with upper valve seat  30  profile, is shown retracted to accommodate the flapper element  24 . The central mandrel  14  is designed to present a lower end face  34  that is shaped in a roughly sinusoidal manner to be generally complimentary to the curved shape of the first axial side  24   a  of the flapper element  24 . Similarly, the lower valve seat  32  also presents a shaped end face  36  that also has a roughly sinusoidal shape to be generally complimentary to the underside  24   b  of the flapper element  24 . The lower valve seat  32  is shown housed within the hinge sleeve  27 . 
   A valve opening assembly, generally indicated at  40 , radially surrounds the flapper element  24  and the central mandrel  14 . The valve opening assembly  40  includes a trigger sleeve  42 , a compression spring  44 , a wicker thread and ratchet mechanism  46 , and an opening sleeve  48 . 
   The trigger sleeve  42  radially surrounds the lug pathway portion  16  of the central mandrel  14  and is axially moveable with respect to the central mandrel  14 . The trigger sleeve  42  includes a radially inwardly projecting lug  50  that engages the lug pathway  16  and is moveable therewithin. It is pointed out that, although only one lug  50  and lug pathway  16  are shown, there might, in practice, be more than one lug  50  and lug pathway  16  associated with the valve assembly  10 . When initially run in to the wellbore, as in  FIG. 1 , the lug  50  is located in the extreme end of the leg portion  18  of the lug pathway  16 . Movement of the lug  50  within the lug pathway  16  will cause compression and release of a lower spring (not shown) in the wicker thread and ratchet mechanism  46 , as is known in the art. 
   The compression spring  44  interconnects the trigger sleeve  42  with the wicker thread and ratchet mechanism  46  of a type known in the art. Opening sleeve  48  radially surrounds the lower portion  32  of the central mandrel  14  and is axially moveable with respect thereto. However, the opening sleeve  48  is affixed to the wicker thread and ratchet mechanism  46 , which provides for incremental one-way motion between the opening sleeve  48  and the central mandrel  14 . In this case, the mechanism  46  allows the opening sleeve  48  to move axially in the uphole direction  12  with respect to the mandrel  14 , while the ratchet engagement prevents movement in the opposite direction. The opening sleeve  48  features a semicylindrical portion  60  and an opening portion  62  that extends approximately ¾ of the distance about the circumference of the lower portion  32 . The opening portion  62  of the opening sleeve  48  presents a pair of rounded shoulders  64  (one shown). 
   When initially run into a wellbore, the flapper element  24  is in the open position shown in  FIG. 1 . A string of washpipe (not shown) is typically disposed within the central mandrel  14 , extending downwardly through and into the lower portion  32  of the central mandrel  14 . The flapper element  24  is held open by the presence of the washpipe at this time. 
   The washpipe is later removed from the central mandrel  14 . When the washpipe is removed, the flapper element  24  closes (see  FIG. 2 ) due to the spring bias of the torsion springs in the hinged attachment  26 . Lugs  28  now align with the opening shoulders  64  of the opening sleeve  48 . 
   Fluid pressure is now increased within the production tubing string of which the valve assembly  10  is a part. The increased fluid pressure causes the central valve mandrel  14  to move down into contact with the flapper element  24 , as illustrated in  FIG. 3 . At this point, the flapper element  24  is positively closed against fluid pressure differentials from either axial direction. Several cycles of pressure increases and decreases may now be accomplished within the tubing string and upper valve seat  30 . 
   To reopen the flapper element  24 , completion of a specific number of pressure cycles is required to allow the lock ring (not shown) to become disengaged. The disengagement of the lock ring enables the central valve mandrel  14  with upper valve seat  34  to be lifted off of the flapper element  24 , as  FIG. 4  depicts. The flapper element  34  is now urged open by actuation of the valve opening assembly  40 . The opening sleeve  48  is moved upwardly as the trigger sleeve  42  moves upwardly with respect to the central mandrel  14 . As this occurs, the lugs  28  of the flapper element  24  ride upwardly upon the curved shoulders  64  of the opening sleeve  48  until the flapper element is in a fully open position (see  FIG. 6 ). Thus, it can be seen that the use of the lug  50  and lug pathway  16  allows the spring  44  to be partially compressed during closing of the flapper element  24  and then fully compressed when the central valve mandrel  14  has been pumped open. Once the valve assembly  10  is vented, the energy stored in the spring  44  is released, allowing the flapper element  24  to be opened via the opening sleeve  48 . 
   It is noted that the mechanical opening mechanism provided by the valve opening assembly  40  and the opening sleeve  48  may be used with flapper valve elements in other types of valve assemblies as well as the isolation valve  10  described herein. 
   The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention.

Summary:
Methods and devices for operation of a flapper valve. A valve assembly is described with a flapper element and a valve opening assembly that will mechanically open the flapper element. The valve opening assembly is particularly valuable where the flapper element fails to open in response to normal hydraulic opening techniques. The valve opening assembly includes a valve opening sleeve having a generally hemispherical cross-section and an opening portion that presents a pair of opening shoulders. The opening shoulders engage lugs on the flapper element so that movement of the opening sleeve will urge the flapper element to an open position. The valve assembly may be run into the wellbore with the flapper element in the open position, rather than having to be closed, as with a number of conventional valve assemblies.