Abstract:
A flapper valve assembly is provided, of the type preventing downward fluid flow when the flapper is closed, which is sized, shaped and configured to provide a smaller maximum outer diameter to minimum internal diameter ratio, thus allowing a larger minimum ID for a given maximum outside diameter, when compared to currently available flapper valve assemblies. An insert assembly is used in the modular saddle flapper valve assembly which has a flapper seat, flapper valve and sleeve. The insert assembly is secured within a tubular housing and enclosed by standard top and bottom subs, either sub being easily removed and replaced with a sub having a different thread size or type, the removal being easily accomplished without disassembly of the insert assembly.

Description:
TECHNICAL FIELD OF THE INVENTION AND INDUSTRIAL APPLICABILITY 
       [0001]    The field of the invention is subterranean well completions, or, more specifically, valve apparatus for preventing flow through a downhole tubular assembly. 
       BACKGROUND OF THE INVENTION 
     Description of Related Art 
       [0002]    Flapper valves, which prevent downward flow when closed, are known to be useful as part of a casing string cemented into a wellbore. The typical flapper valve will be open as the casing string is run into the well and cemented into place. It is common in such applications, for a flapper valve to be run into a well having a 6.125 in. (15.56 cm) hole diameter, as part of a 3.5 in. (8.89 cm) outside diameter (OD) casing string having a nominal internal diameter (ID) of approximately 3.0 in. (7.62 cm). The 6.125 in. (15.56 cm) hole dictates that the flapper valve outside diameter cannot practically exceed 5.875 in. (14.92 cm). 
         [0003]    In the foregoing field situation, it is desirable to use 4.5 in. (11.43 cm) outside diameter casing string, (grade P110, 13.5 pounds per foot (6.12 kg per 30.48 cm) having a nominal internal diameter (ID) of 3.92 in. (9.96 cm), in lieu of the 3.5 in (8.89 cm) OD casing. This ID dictates that a practical flapper valve minimum ID be at least 3.8 in. (9.65 cm) to substantially take advantage of the increased ID of the 4.5 in. (11.43 cm) OD casing. Similarly, anything less causes a restriction in the casing ID that unacceptably prevents the passage of typically associated tools such as bridge plugs, shifting tools, and mechanical packers, some of which have maximum outside diameters of as high as 3.66 in. (9.30 cm). However, no currently available flapper valves, with the required maximum OD of 5.875 in. (14.92 cm), can provide the minimum ID of approximately 3.8 in. (9.65 cm) that would be compatible with the desired 4.5 in. (11.43) OD casing. Operators using currently available flapper valves are limited to the 3.5 in. (8.89 cm) OD casing in a 6.125 in. (15.56 cm) well hole. 
         [0004]    Again, with respect to flapper valve assemblies that prevent downward fluid flow when closed, it is not uncommon in current practice for various components in the casing string to require that flapper valves have top and bottom ends with varying thread sizes and types to accommodate the varying pins, collars and boxes to which flapper valves are sometimes attached as the string is assembled. Currently available flapper valves have ends integrated with housing and/or flapper seat structure, or additional structure, generally, which prevent the ready replacement of a flapper valve assembly ends with ends having a different thread size or type. 
         [0005]    Additionally, the assembly of flapper valve assemblies is generally complicated when the flapper seat, with flapper attached, has been previously integrated with housing structure and the flapper must be held open by inserting temporary, elongated devices into the housing. As the sleeve is then inserted, it is impossible to see the interaction between the flapper, which is biased to close, and the sleeve which must encounter and move the flapper to its full open position as it is inserted. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention overcomes the shortcomings of the prior art by providing a flapper valve assembly, of the type preventing downward fluid flow when the flapper is closed, which is sized, shaped and configured to provide a smaller maximum outer diameter to minimum internal diameter ratio, thus allowing a larger minimum ID for a given maximum outside diameter, when compared to currently available flapper valve assemblies. Additionally, the present invention provides a modular saddle flapper valve assembly which provides an insert assembly having a flapper seat, flapper valve and sleeve, the insert assembly being secured within a tubular housing and enclosed by standard top and bottom subs, either sub being easily removed and replaced with a sub having a different thread size or type, the removal causing no disturbance to or disassembly of the insert assembly. 
         [0007]    In some exemplary embodiments of our invention we have provided, a flapper valve assembly for inclusion in a downhole tubular assembly, the flapper valve assembly comprising: a tubular housing having an interior pocket, the pocket having an inside surface, the tubular housing further having a removable top member forming a tubular housing upper end, and a removable bottom member forming a tubular housing lower end, the bottom member having a top, the upper and lower ends each being attachable within the downhole tubular assembly; and an insert assembly, the insert assembly being insertable into the tubular housing pocket when the top member is removed, and retained within the pocket when the top member is attached, the insert assembly, the insert assembly having: a flapper seat, the flapper seat being substantially sealed against the tubular housing interior pocket inside surface; a flapper having a curved portion, the flapper being movable between a down position and an up position; a bias member biasing the flapper from the up position to the down position; and a sleeve upwardly slidably from a sleeve first position upon the flapper seat, the flapper seat preventing downward movement of the sleeve, to a sleeve second position, such that the flapper is held in the up position when the sleeve is in the first position, the bias member moving the flapper to the down position when the sleeve is in the second position, the sleeve further having a top portion having an outside diameter, and a bottom portion having an outside diameter smaller than the top portion, the sleeve top portion being substantially sealed against the tubular housing interior pocket inside surface, the sleeve bottom portion being saddled by the flapper curved portion when the sleeve is in the first position; wherein flow from the tubular housing pocket through the tubular housing lower end is prevented when the flapper is in the down position and allowed when the flapper is in the up position. 
         [0008]    In some exemplary embodiments, the flapper seat further comprises side portions, the side portions having top, inwardly directed bevels; and further the flapper is positioned between the flapper seat side portions when the flapper is in the down position, the flapper being guided by the flapper seat side portion bevels to the down position between the flapper seat side portions, the flapper seat side portions resisting and/or substantially preventing lateral movement of the flapper during flapper deformation. 
         [0009]    In some exemplary embodiments, the flapper further has opposing side edges and a front edge, and the flapper seat further has an elevation about at least part of the flapper side and front edges, the elevation having a top, inwardly directed bevel; and further wherein the flapper is positioned within the elevation when the flapper is in the down position, the flapper being guided by the flapper seat elevation bevel to the down position within the elevation, the flapper seat elevation resisting and/or substantially preventing lateral movement of the flapper during flapper deformation. 
         [0010]    In some exemplary embodiments, the flapper valve assembly further comprises a plurality of pins, and further the flapper seat has side portions and a curved surface disposed between the side portions, each side portion having at least one pin hole for receiving at least one of the pins, and the flapper seat curved surface having at least one pin hole for receiving at least one of the pins, the flapper curved portion having first and second edges and a forward edge, the flapper curved portion being sized such that when the flapper is in the down position, the flapper curved portion first edge is proximate the at least one pin in the flapper seat first side portion, the flapper curved portion second edge is proximate the at least one pin in the flapper seat second side portion, and the flapper curved portion forward edge is proximate the at least one pin in the flapper seat curved surface. In some exemplary embodiments, the flapper valve assembly further comprises a pair of guide members, each guide member being attachable to one of the flapper seat side portions using the at least one pin received by such side portion, each guide member being shaped and attachably positioned such that one of the flapper curved portion edges is proximate the guide member when the flapper is in the down position. In some exemplary embodiments, the each of the guide members has an inside surface, the inside surface having a top bevel, the bevel being positioned to guide the descending flapper into the flapper&#39;s down position between the guide members. 
         [0011]    In some exemplary embodiments, the sleeve has a minimum internal diameter and the flapper valve assembly has a maximum outer diameter, the ratio of the maximum outer diameter to the sleeve minimum inside diameter being 1.55 or less. In some exemplary embodiments, the tubular housing has a wall, the wall having a thickness, the wall thickness to flapper valve assembly maximum outer diameter ratio being 0.0625 or greater. 
         [0012]    In some exemplary embodiments: the tubular housing bottom member has a bottom end for attachment to a first downhole tubular assembly component, the bottom end having a first attachment configuration; and the flapper valve assembly further comprises a tubular housing substitute bottom member, the substitute bottom member having a bottom end for attachment to a second downhole tubular assembly component, the bottom end having a second attachment configuration, the second attachment configuration being different from the first attachment configuration. 
         [0013]    In some exemplary embodiments: the sleeve top portion further comprises at least one channel, the at least one channel being positioned about at least a portion of the sleeve top portion circumference; the tubular housing has at least one hole, the at least one hole being aligned with one of the at least one sleeve top portion channels when the top portion is supported by the flapper seat and the flapper seat is supported by the tubular housing bottom member top; and at least one shear member for insertion into one of the at least one holes and protrusion into one of the at least one sleeve top portion channels; wherein the inserted at least one shear member retains the sleeve within the tubular housing with the tubular housing top member removed. 
         [0014]    In some exemplary embodiments: the tubular housing top member has a top end for attachment to a first downhole tubular assembly component, the top end having a first attachment configuration; and the flapper valve assembly further comprises a tubular housing substitute top member, the substitute top member having a top end for attachment to a second downhole tubular assembly component, the top end having a second attachment configuration, the second attachment configuration being different from the first attachment configuration. 
         [0015]    In some exemplary embodiments, the tubular housing, the tubular housing top member and the tubular housing bottom member have substantially equal outside diameters. In some exemplary embodiments, the insert assembly is attached to the bottom member top. In some exemplary embodiments, the bottom member top forms an upwardly facing interior shoulder, the shoulder supporting the inserted insert assembly. 
         [0016]    In some exemplary embodiments: the flapper seat further comprises at least one channel, the at least one channel being positioned about at least a portion of the flapper seat circumference; the tubular housing has at least one threaded hole, the at least one hole being aligned with one of the at least one flapper seat channels when the flapper seat is supported by the tubular housing bottom member top; and at least one threaded fastener for threaded insertion into one of the at least one threaded holes and protrusion into one of the at least one flapper seat channels; wherein the inserted at least one fastener retains the flapper seat within the tubular housing with the tubular housing bottom member removed. 
         [0017]    In some exemplary embodiments of our invention we have provided a flapper valve assembly for inclusion in a downhole tubular assembly, the flapper valve assembly comprising: a tubular housing having an interior pocket, the pocket having an inside surface, the tubular housing further having a removable top member forming a tubular housing upper end, and a removable bottom member forming a tubular housing lower end, the bottom member having a top, the upper and lower ends each being attachable within the downhole tubular assembly; and insert assembly means, the insert assembly means being insertable into the tubular housing pocket when the top member is removed, and retained within the pocket when the top member is attached, the insert assembly means having: flapper seat means, the flapper seat means being substantially sealed against the tubular housing interior pocket inside surface; flapper means having a flapper, the flapper having a curved portion, the flapper being movable between a down position and an up position; bias means for biasing the flapper from the up position to the down position; and sleeve means having a sleeve, the sleeve being upwardly slidably from a sleeve first position upon the flapper seat means, the flapper seat means preventing downward movement of the sleeve, to a sleeve second position, such that the flapper is held in the up position when the sleeve is in the first position, the bias means moving the flapper to the down position when the sleeve is in the second position, the sleeve further having a top portion having an outside diameter, and a bottom portion having an outside diameter smaller than the top portion, the sleeve top portion being substantially sealed against the tubular housing interior pocket inside surface, the sleeve bottom portion being saddled by the flapper curved portion when the sleeve is in the first position; wherein flow from the tubular housing pocket through the tubular housing lower end is prevented when the flapper is in the down position and allowed when the flapper is in the up position. 
         [0018]    In some exemplary embodiments of the present invention, the flapper valve assembly further comprises means for substantially preventing lateral movement of the flapper curved portion during deformation of the flapper in response to pressure on the flapper curved portion. 
         [0019]    The foregoing features and advantages of our invention will be apparent from the following more particular descriptions of exemplary embodiments of the invention as illustrated, for some embodiments, in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a sectional view of the tubular housing in an exemplary embodiment of the present invention. 
           [0021]      FIG. 2  is a rear view of the insert assembly in an exemplary embodiment of the present invention. 
           [0022]      FIG. 3  is a perspective view of the flapper seat and flapper in an exemplary embodiment of the present invention, with the flapper in the down position. 
           [0023]      FIG. 4  is a side view of the insert assembly in an exemplary embodiment of the present invention. 
           [0024]      FIG. 5  is a side view of the sleeve in an exemplary embodiment of the present invention. 
           [0025]      FIG. 5A  is a sectional side view of a sleeve in an exemplary embodiment of the present invention. 
           [0026]      FIG. 6  is a rear perspective view of the flapper seat and flapper in an exemplary embodiment of the present invention. 
           [0027]      FIG. 7  is a side view of the flapper seat and flapper in an exemplary embodiment of the present invention. 
           [0028]      FIG. 8  is a top view of the flapper seat in an exemplary embodiment of the present invention. 
           [0029]      FIG. 9  is a top rear perspective view of the flapper seat in an exemplary embodiment of the present invention. 
           [0030]      FIG. 10  is a side view of the flapper seat in an exemplary embodiment of the present invention. 
           [0031]      FIG. 11  is a rear view of the flapper seat in an exemplary embodiment of the present invention. 
           [0032]      FIG. 12  is a top rear perspective view of the flapper in an exemplary embodiment of the present invention. 
           [0033]      FIG. 13  is a side view of the flapper in an exemplary embodiment of the present invention. 
           [0034]      FIG. 14  is a front top perspective view of the flapper in an exemplary embodiment of the present invention. 
           [0035]      FIG. 15  is a bottom side perspective view of the flapper in an exemplary embodiment of the present invention. 
           [0036]      FIG. 16  is a perspective view of a flapper seat in an exemplary embodiment of the present invention. 
           [0037]      FIG. 17  is a detail view of the portion of the flapper seat in  FIG. 16 , encompassed by circle A. 
           [0038]      FIG. 18  is a side view of the flapper seat of  FIG. 16 , with pin holes shown in broken line. 
           [0039]      FIG. 19  is a side view of the flapper seat of  FIG. 16 , with pin holes shown in broken line. 
           [0040]      FIG. 20  is a top view of the flapper seat of  FIG. 16 . 
           [0041]      FIG. 21  is a top view of a flapper in an exemplary embodiment of the present invention. 
           [0042]      FIG. 22  is a side view of the flapper of  FIG. 211 . 
           [0043]      FIG. 23  is an end view of the flapper of  FIG. 211 . 
           [0044]      FIG. 24  is a sectional side view of the flapper of  FIG. 21 . 
           [0045]      FIG. 25  is a side view of a pin used in exemplary embodiments of the present invention. 
           [0046]      FIG. 26  is a perspective view of the insert assembly of an exemplary embodiment of the present invention with the flapper closed. 
           [0047]      FIG. 27  is a perspective view of the insert assembly of an exemplary embodiment of the present invention with the flapper open. 
           [0048]      FIG. 28  is an exploded view of the insert assembly of an exemplary embodiment of the present invention. 
           [0049]      FIG. 29  is a perspective view of the flapper seat of an exemplary embodiment of the present invention. 
           [0050]      FIG. 30  is a top view of the flapper seat of an exemplary embodiment of the present invention. 
           [0051]      FIG. 31  is a side view of the flapper seat of an exemplary embodiment of the present invention. 
           [0052]      FIG. 32  is a rear view of the flapper seat of an exemplary embodiment of the present invention. 
           [0053]      FIG. 33  is a side sectional view of the flapper seat of an exemplary embodiment of the present invention, viewed along section line  33 - 33  in  FIG. 32 . 
           [0054]      FIG. 34  is a top view of the flapper of an exemplary embodiment of the present invention. 
           [0055]      FIG. 35  is a side view of the flapper of an exemplary embodiment of the present invention. 
           [0056]      FIG. 36  is a front view of the flapper of an exemplary embodiment of the present invention. 
           [0057]      FIG. 37  is a side sectional view of the flapper of an exemplary embodiment of the present invention, viewed along section line  37 - 37  in  FIG. 36 . 
           [0058]      FIG. 38  is a perspective view of the guide wall of an exemplary embodiment of the present invention. 
           [0059]      FIG. 39  is an end view of the guide wall of an exemplary embodiment of the present invention. 
           [0060]      FIG. 40  is a top view of the guide wall of an exemplary embodiment of the present invention. 
           [0061]      FIG. 41  is a side view of the guide wall of an exemplary embodiment of the present invention. 
           [0062]      FIG. 42  is a bottom view of the guide wall of an exemplary embodiment of the present invention. 
           [0063]      FIG. 43  is a top view of the insert assembly of an exemplary embodiment of the present invention with the flapper closed. 
           [0064]      FIG. 44  is a first side view of the insert assembly of an exemplary embodiment of the present invention with the flapper closed. 
           [0065]      FIG. 45  is a second side view of the insert assembly of an exemplary embodiment of the present invention with the flapper closed. 
           [0066]      FIG. 46  is a front view of the insert assembly of an exemplary embodiment of the present invention with the flapper closed. 
           [0067]      FIG. 47  is a top view of the insert assembly of an exemplary embodiment of the present invention with the flapper open. 
           [0068]      FIG. 48  is a first side view of the insert assembly of an exemplary embodiment of the present invention with the flapper open. 
           [0069]      FIG. 49  is a rear view of the insert assembly of an exemplary embodiment of the present invention with the flapper open. 
           [0070]      FIG. 50  is a second side view of the insert assembly of an exemplary embodiment of the present invention with the flapper open. 
           [0071]      FIG. 51  is a side view of an exemplary embodiment of the present invention. 
           [0072]      FIG. 52  is a sectional side view of an exemplary embodiment of the present invention cut along section line  52 - 52  in  FIG. 51 . 
           [0073]      FIG. 53  is a sectional side view of the tubular housing of an exemplary embodiment of the present invention cut along its longitudinal center line. 
           [0074]      FIG. 54  is a sectional side view of the top sub of an exemplary embodiment of the present invention cut along its longitudinal center line. 
           [0075]      FIG. 55  is a sectional side view of the bottom sub of an exemplary embodiment of the present invention cut along its longitudinal center line. 
           [0076]      FIG. 56  is a perspective view of the insert assembly of an exemplary embodiment of the present invention with the flapper closed. 
           [0077]      FIG. 57  is a perspective view of the insert assembly of an exemplary embodiment of the present invention with the flapper closed. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0078]    The following discussion describes exemplary embodiments of the invention in detail. This discussion should not be construed, however, as limiting the invention to those particular embodiments. Practitioners skilled in the art will recognize numerous other embodiments as well. 
       Definitions 
       [0079]    Unless specifically indicated otherwise, terms such as “up,” “upward,” “down,” “downward,” “highest,” “lowest,” “above,” “below,” and other terms suggesting a vertical movement, position or relationship, as used herein, refer to positions along, and/or with respect to, the wellbore axis, with the distal end of the wellbore being considered the lowermost, and the surface end being considered the uppermost. Accordingly, movement “up” is toward the surface within the wellbore, although the true path may actually be horizontal, or even downward, with respect to the surface. Similarly, a point “lower” than another point would be farther from the surface, along the wellbore axis, although the points may actually be on an equal plane with respect to the surface. 
         [0080]    The term “running,” as used herein, refers to moving downward into the well with whatever is indicated as being run. The term “pulling,” as used herein, refers to moving upward within a well with whatever is indicated as being pulled. 
         [0081]    The term “well,” as used herein, refers to holes drilled vertically, at least in part, and may also refer to holes drilled with deviated, highly deviated, and/or horizontal sections of the wellbore. The term also includes wellhead equipment, surface casing, intermediate casing, and the like, typically associated with oil and gas wells. 
         [0082]    The term “target completion interval,” as used herein, refers to a portion of a subterranean formation from which an operator wishes to allow flow of fluids into the well. The term includes both a single formation having one or more such portions (typically the case in a horizontal well) and multiple formations penetrated by the wellbore (typically the case in a vertical well), with each formation being a targeted portion. 
         [0083]    The term “frac job,” as used herein, refers to treatment of a hydrocarbon formation, whereby fluids are injected into the formation causing fractures to occur and to enlarge. In some instances, proppants, such as sand, are included in the injection fluid, the proppants being retained within the enlarged fractures, such that the fractures are prevented from fully closing after the injection of the fluid ceases. 
         [0084]    As used herein, the term “downhole tubular assembly” means an assembly of components chosen to perform various downhole functions purposes in fluid producing wells, the functions being enabled, at least in part, by the ability of the present invention to be integrated within the assembly and act as a valve with an open and closed position. Such assemblies include, without implied limitation, a production casing string (or a liner) cemented in a drilled hole, which has an exemplary embodiment of the valve of the present invention fastened between two joints of the casing, the casing or liner extending through one or more target completion intervals. In such an example, the “downhole tubular assembly” will often include joints of casing, casing collars, casing centralizers, and the like. For this example, the valve of the present invention will be included within the other components, usually with a casing joint above (pin down) and a casing collar below, and will be open as the components are assembled and run into the well, and during cementing. An example of a flapper valve assembly being included within a downhole tubular assembly is disclosed, generally, in United States Patent Application 2006/0124315, which is incorporated herein by reference. 
         [0085]    As used herein, the term “shifting tool” refers to a conventional tool run into a well, which when properly positioned and manipulated, will physically move a sleeve within a downhole tool from a lower position to an upper position. An example of such a tool is the Otis Type B Shifting Tool. A shifting tool will typically have expandable keys (“dogs”) which expand within a larger internal diameter portion of a sleeve and encounter an interior sleeve profile such that the sleeve is pulled as the shifting tool is pulled. This interaction with the sleeve interior is well known in the art. 
       DETAILED DESCRIPTION 
       [0086]    Turning now to  FIGS. 1-5 , wherein an exemplary embodiment of the present invention is illustrated. In this exemplary embodiment, and as illustrated in  FIG. 1 , a tubular housing assembly  10  has a tubular housing  20  having an interior pocket  22  with an inside surface  24 . The tubular housing is threadably attached to a top member (“top sub”)  26  having a bottom end  28 , a top end  30  with threads  32  usable for attachment to a downhole tubular assembly component, such as a casing joint pin. The top sub  26  attachment to the tubular housing is sealed using O-rings  34 . The tubular housing  20  is further threadably attached to a bottom member (“bottom sub”)  40  having a top end  42 , forming an upwardly facing shoulder  44  adjacent the interior pocket  22 , and a bottom end  46  with threads  48  usable for attachment to a downhole tubular assembly component, such as a casing collar. The bottom sub  40  attachment to the tubular housing is sealed using O-rings  50 . The tubular housing  20  further has six circumferentially spaced threaded holes  52  (four shown) extending through the tubular housing  20  into the interior pocket  22 , and two circumferentially spaced shear member, i.e. shear screw holes  54  extending through the tubular housing into the interior pocket. The threaded holes  52  threadably receive conventional ¾ in. (19.05 mm) by ⅜ in. (9.52 mm) steel set screws (not shown), with machine threads in this exemplary embodiment. The shear screw holes  54  are sized to secure conventional ¾ in. (19.05 mm) by ¼ in. (6.35 mm) brass shear screws (not shown). 
         [0087]    Turning now to  FIG. 2 , wherein an insert assembly  60  is depicted for an exemplary embodiment of the present invention (not necessarily to scale). The insert assembly includes a flapper seat  70 , a flapper  80 , a bias member (a spring  82  in this exemplary embodiment), a bias member pin  83  and a slidable sleeve  90 . The flapper seat has a bottom  72 , a curved upper face  74 , two ears  76   a,b , the ears having holes  77   a,b  for receiving the pin  83 , a first circumferential channel  78  and a second circumferential channel  79 . When the bottom sub  40  is attached, the insert assembly  60  is supported by the interior shoulder  44  formed by the bottom sub  40 , and the first channel  78  is in vertical alignment with the six set screw holes  52 , the first channel  78  being sized to receive the ends of the six set screws as the screws are threaded into place. When the set screws are in place within the flapper seat first channel  78  and bear upon the flapper seat  70 , the flapper seat  70  is fixed within the tubular housing interior pocket  22 . The flapper seat second circumferential channel  79  is sized to receive a conventional O-ring (not shown), the O-ring sealing the flapper seat  70  against the tubular housing interior pocket inside surface  24  as the insert assembly  60  is inserted into the interior pocket  22 . 
         [0088]    In the exemplary embodiment of the present invention depicted in  FIGS. 2-5 , the curved flapper  80  has a top surface  84 , a bottom surface  86  and two ears  88   a,b  having holes  89   a,b  for alignment with the flapper seat ear holes  77   a,b , for insertion of the bias member pin  83  through both sets of ears  77   a,b ,  89   a,b  and the spring  82 , as further illustrated in  FIG. 2 . The spring  82  has a first end  82   a  extending onto the flapper top surface  84 , and a second end  82   b  extending into a hole  71  in the flapper seat  80 , such that the spring  82  is forced into compression as the flapper  80  is lifted from the flapper seat  70 . The flapper bottom surface  86  covers and seals the flapper seat  70 , as illustrated in  FIG. 3 , when the flapper  80  is in the down position. 
         [0089]    As illustrated in  FIG. 2  and  FIG. 4 , the sleeve  90  is positioned on the flapper seat  70  with the flapper  80  in an open position as the insert assembly  60  is inserted into the tubular housing interior pocket  22  through the opening made by removing the top sub  26 . The sleeve  90  has a top portion  92  with a larger outside diameter and inside diameter than the sleeve&#39;s bottom portion  94 . As discussed above, the larger inside diameter of the sleeve top portion  92  allows for shifting tool dogs to expand and engage an sleeve top portion interior profile (not shown). The sleeve top portion  92  has a first circumferential channel  96  that is vertically aligned with the shear screw holes  54 , and is sized to receive the ends of the shear screws as the shear screws are fixed in the shear screw holes  54 . The sleeve top portion  92  also has a second circumferential channel  97  for receiving an O-ring (not shown) that causes the sleeve top portion  92  to seal against the interior pocket inside surface  24 . 
         [0090]    In such exemplary embodiments, when the shear screws are in place within the sleeve top portion first channel  96 , the sleeve  90  is fixed within the tubular housing interior pocket  22 . The shear screws prevent the sleeve  90  from moving upwardly within the tubular housing interior pocket  22 , while the flapper seat  70  prevents the sleeve  90  from moving downwardly. Accordingly, the insert assembly  60  is secured within the tubular housing interior pocket  22  when the insert assembly  60  bears upon the interior shoulder  44  formed by the bottom sub  40  and the shear screws have extended through shear screw holes  54  in the tubular housing  20  into the sleeve top portion first channel  96 . These shear screws are sheared when the sleeve  90  is pulled by a shifting tool. Additional securement is provided by the set screws that protrude into the flapper seat first channel  78 . Further, the O-rings in the flapper seat second channel  79  and the sleeve top portion second channel  97  seal the flapper seat  70  and sleeve top portion  92  against the interior pocket inside surface  22 . 
         [0091]    In the exemplary embodiments of the present invention depicted in  FIGS. 1-5 , the sleeve lower portion  94  has a lower surface  98  that is shaped for bearing upon and covering the opening in the flapper seat upper face  74  when the flapper  80  is open. This protects the flapper seat from sand, during frac jobs, and cement slurry, during cementing operations. As a result, and in combination with the sealing of the sleeve top portion  92  and flapper seat  70  against the interior pocket inside surface  24 , fluids entering through the top sub  26  are forced into the insert assembly  60  and held within the insert assembly  60  until discharged through the bottom sub  40 . This substantially isolates the flapper  80  and spring  82  from well fluids while the flapper  80  is open. 
         [0092]    Turning now to  FIG. 5A , wherein a sleeve  90  is depicted for an exemplary embodiment of the present invention. During operation, where the sleeve  90  is internally pressured, it is beneficial to allow pressure equalization between the sleeve interior  120  and the interior pocket  22 . Pressure equalization is accomplished through four weep holes  93   a - c  (three shown) spaced circumferentially about the sleeve top portion  92 , and, to some extent, through the interface between the sleeve lower surface  98  and the flapper seat upper face  74 . The sleeve interior  120  includes an sleeve interior profile  122  formed by a reduced internal diameter of the sleeve interior. As discussed above, a shifting tool will typically have expandable keys (“dogs”) which expand within this larger internal diameter portion of the sleeve interior and will encounter the sleeve interior profile  122  such that the sleeve  90  is pulled as the shifting tool is pulled. 
         [0093]    In such exemplary embodiments, it is to be noted that both the top sub  26  and the bottom sub  40  may be removed without disturbing the insert assembly  60 . This modular construction allows an operator to readily exchange the bottom sub  40 , for example, for another bottom sub having a different thread  48  size or type. The top sub  26  is analogously interchangeable with top subs with different thread  32  sizes and types on the top sub top end. 
         [0094]    A notable advantage of the present invention, made possible by the provision of the insert assembly  60 , is that manufacturing assembly is greatly simplified by the simultaneous insertion of the flapper seat  70 , open flapper  80 , and positioned sleeve  90 . It is not necessary to hold a pre-integrated flapper in an open position while a sleeve is inserted, as is currently the case. 
         [0095]    Turning now to  FIGS. 6-15 , wherein an exemplary embodiment of a flapper seat  100  and an attached flapper  110  are illustrated, along with individual depictions of the flapper seat  100  and the flapper  110 . The relative dimensions of the flapper seat  100  and the flapper  110  are substantially to scale, and illustrate the relative shapes of the flapper lower face  112  and the flapper seat upper face  102 . Also illustrated is the flapper seat first channel  106 , second channel  107 , bottom end  108 , and flapper top surface  116 . [In this exemplary embodiment, the flapper ears  114   a,b  are positioned inside the flapper seat single ear  104 . The spring is not shown, but is of analogous function to that of spring  82 .] In this exemplary embodiment of the present invention, the above-described field situation is specifically addressed in which it is desirable to run a downhole tubular assembly having 4.5 in. (11.43 cm) outside diameter (OD) casing (3.92 in. (9.96 cm) nominal internal diameter (ID)) into a 6.125 in. (15.56 cm) diameter hole. As indicated above, this hole size dictates that the maximum outside diameter of a flapper valve assembly, of any type, is limited to approximately 5.875 in. (14.92 cm), and no current flapper valve assembly having such an outside diameter can provide the required minimum internal diameter of approximately 3.8 in. (9.65 cm). In accordance with the limitations dictated by the conditions of this field situation, it is clear that an acceptable ratio of the maximum outside diameter of the flapper valve assembly to the minimum internal diameter of the flapper valve assembly will be equal to approximately 1.55 (5.875 in. (14.92 cm) divided by 3.8 in. (9.65 cm). As this ratio becomes smaller, larger and larger casing sizes are usable for a flapper valve assembly having a fixed maximum outside diameter. Similarly, as the ratio becomes smaller, and the casing size is fixed, a smaller and smaller well hole size will be available for the casing. Conversely, as the ratio becomes larger a larger maximum outside diameter is required for a given casing size. 
         [0096]    Exemplary embodiments of the type depicted in  FIGS. 6-15 , are shaped, sized and configured, such that the flapper seat  100  will be insertable into a tubular housing having a maximum OD of 5.875 in. (14.92 cm) with an acceptable tubular housing wall thickness of approximately 0.5 in. (12.7 mm) adjacent the flapper seat  100 . The sleeve in such embodiments has a minimum ID of approximately 3.8 in. (9.65 cm) and a lower portion wall thickness of approximately 0.025-0.125 in. (0.63-3.17 mm) The minimum ID of the flapper seat  100  is 3.8 in. (9.65 cm). Accordingly, when the flapper seat in such exemplary embodiments is constructed with components having dimensions proportional to those shown in  FIGS. 6-15 , the finished flapper valve assembly will be usable with the 4.5 in. (11.43 cm) OD casing in the 6.125 in. (15.56 cm) hole as described above. 
         [0097]    A wall thickness of at least approximately ⅜ in (9.5 mm) will be acceptable for the tubular housing in exemplary embodiments of the present invention, depending on the material used in its construction. 
         [0098]    Table 1 below provides information relevant to the foregoing ratio with respect to the prior art and exemplary embodiments of the present invention represented by  FIGS. 6-15 . The prior art includes the disclosures of representative patents and published patent applications, where a flapper, flapper seat and sleeve are present, where downward flow is prevented by the closed flapper. [Inclusion of such prior art devices herein does not imply that a particular prior art example is usable in a manner similar to the present invention.] Maximum outside diameter (“MOD”) was set at 5.875 in. (14.92 cm.) with the minimum internal diameter (“MID”) being determined by scaling from the assumed 5.875 in. (14.92 cm.) outside diameter, using measurements taken from an appropriate figure in the patent. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 5.875 INCH (14.92 CM.) 
               
               
                   
                   
                 EQUIVALENT 
               
               
                   
                   
                 MAXIMUM INTERNAL 
               
               
                   
                   
                 DIAMETER 
               
               
                   
                   
                 AVAILABLE WITH 
               
               
                   
                 RATIO - 
                 5.875 INCH (14.92 CM.) 
               
               
                 TOOLS 
                 MOD/MID 
                 MOD LIMITATION 
               
               
                   
               
             
             
               
                 Hernandez &amp; Klatt 
                 1.55 
                  3.8 in. (9.65 cm) 
               
               
                 US App. 2006/0124315 
                 1.65 
                 3.56 in. (9.04 cm) 
               
               
                 (FIG. 4) 
               
               
                 US App. 2006/0124311 
                 2.57 
                 2.29 in. (5.82 cm) 
               
               
                 (FIG. 2) 
               
               
                 U.S. Pat. No. 6,328,109 
                 1.69 
                 3.48 in. (8.84 cm) 
               
               
                 (FIG. 3B) 
               
               
                   
               
             
          
         
       
     
         [0099]    From Table 1 it shown that only the present invention can satisfy the 3.8 in. (9.65 cm) minimum internal diameter required. 
         [0100]    For some exemplary embodiments of the present invention, construction materials include 4140 steel for the top sub  26  and bottom sub  40 , nitride frac hardened steel for the flapper seat  70  and sleeve  90 , cast iron for the flapper  80 , and 4340 steel for the tubular housing  20 . 
         [0101]    Prospectively, it is anticipated that the torsion spring  82  will be constructed from 0.0720 in. (1.83 mm) oil tempered steel spring wire (heat number 307096; ASTM-A-229-99 Class 1) in some exemplary embodiments. 
         [0102]    Turning now to  FIGS. 16-25 , wherein an exemplary embodiment of the present invention is shown to include a flapper seat  200  and flapper  250 , the flapper seat having an upper face having a curved portion  204  and opposing, substantially flat, first and second side portions  206 , 208 , the first side portion  206  having two, substantially vertically oriented pin holes  210   a,b , the second side portion  208  having two, substantially vertically oriented pin holes  212   a,b . In exemplary embodiments of the type illustrated in  FIGS. 16-25 , the flapper seat upper face curved portion  204  has a pin hole  214  positioned opposite from bias member first and second ears  216 , 218 , the bias member ears being contoured and shaped such that the ears outer edges  220 , 222  are substantially flush with the flapper seat exterior side surface  224 . As shown in  FIG. 25 , pins  260  are insertable in the pin holes  210   a,b ,  212   a,b ,  214 , each pin having an upper end  262  protruding from the pin hole. In some exemplary embodiments the upper end is beveled, and in some exemplary embodiments, the bevel is formed at approximately 30 degrees from horizontal. In some exemplary embodiments, a conventional adhesive, is used to secure the shear member pins  260  in the pin holes  210   a,b , 212   a,b , 214 , with the bevels declining inwardly. 
         [0103]    As illustrated in  FIGS. 21-24 , the flapper  250  in exemplary embodiments of the type illustrated in  FIGS. 16-25 , is shaped in substantially similar fashion as shown in  FIGS. 21-24 . The flapper has a curved surface  252 , first and second edges  254 , 256 , and a forward edge  258 , the distance between the first edge  254  and the second edge  256  being no larger than the distance between the flapper seat side portions  206 , 208 , such that when the flapper is lowered to a position where the flapper curved surface  252  is against the flapper seat curved portion  204 , the flapper first edge  254  is proximate the pins  260  in the flapper seat first side portion pin holes  210   a,b , the flapper second edge  256  is proximate the pins in the flapper seat second side portion pin holes  212   a,b , and the flapper forward edge  258  is proximate the pin in the flapper seat upper face curved portion pin hole  214 . The pins  260  are originally positioned in the pin holes  210   a,b , 212   a,b , 214  with the bevels declining inwardly, such that as the flapper  250  closes, it will be guided, if needed, to the proper position and will not come to rest upon the upper end  262  of any pin  260 . In operation, when the flapper  250  is so positioned with respect to the pins  260 , and pressure is applied through the sleeve  90  to the flapper, the pins prevent the movement of the flapper first and second edges  254 , 256  in an outward direction, i.e. flattening of the flapper is prevented. Use of the pins  260  for this purpose allows the flapper thickness to be reduced from a thickness otherwise required to prevent flattening in the absence of the pins at higher pressures. 
         [0104]    Pins  260  for use in the flapper seat pin holes  210   a,b , 212   a,b ,  214  are constructed from conventional drill rod in some exemplary embodiments. In some exemplary embodiments the pins are constructed from plain hardened steel having a double shear strength of approximately 12,800 pounds (5,806 kg), with a Rockwell hardness of C50, as described in the American Society of Mechanical Engineers specification ASME B 18.8.2, effective as of the date of this application. In some exemplary embodiments the pin diameter is approximately ¼ in. (6.35 mm) and overall length approximately ¾ in. (12.7 mm) In some exemplary embodiments the pin diameter is 5/16 in. (7.94 mm) In some exemplary embodiments the flapper  250  is constructed from cast iron bar stock, including heat treated ductile iron having approximately 100,000 psi (689476 kPa) tensile strength, approximately 70,000 psi (482,633 kPa) yield strength, and an approximately 3 percent elongation rating. 
         [0105]    In tests, exemplary embodiments have been tested and shown to withstand approximately 7800 psi (53,7779 kPa) of differential pressure on the closed flapper, when the flapper was 0.35″ at its thickest point, and approximately 9800 psi (67,569 kPa) of differential pressure when the flapper was 0.44 in. (11.18 mm) at its thickest point. 
         [0106]    Turning now to  FIGS. 26-50 , wherein an exemplary embodiment  300  of the present invention is depicted and shown to include a flapper seat  302  and flapper of  350  of similar construction to the flapper seat  200  and the flapper  250  depicted in  FIGS. 16-25 , and also includes five pin holes  310   a,b ,  312 , a,b ,  314  corresponding to the five pin holes  210   a,b , 212   a,b , 214  shown in  FIGS. 16-25 . Five pins  260  are also shown. In some exemplary embodiments guide walls  370 , 372  are pinable to the first and second side portions  306 , 308  as further illustrated in the exploded view provided in  FIG. 31 . As illustrated in more detail in  FIGS. 38-42 , each guide wall  372 , 374  has a substantially flat inside surface  376 , 378  extending upwardly to a downwardly sloping bevel  380 , 382 , with a substantially flat top surface  384 , 386  and bottom surface  385 , 387 . Each guide wall has an exterior curved surface  388 , 390  shaped to follow the exterior circumference of the flapper seat  300 . Penetrating each of the guide walls  372 , 374  are two pin holes  392   a,b , 394   a,b . each pair alignable with corresponding pairs of pin holes  310   a,b , 312   a,b  for receiving a pin  260  through the guide wall  372 , 374  and then into the flapper seat  350 . As shown in  FIGS. 26-28 , the guide walls so pinned are substantially flush to the flapper seat first and second side portions  306 , 308 , and to the outer surface of the flapper seat. 
         [0107]    As further illustrated for exemplary embodiments of the type illustrated in  FIGS. 26-50 , the closed views provided in  FIGS. 43-46 , in particular, illustrate that the flapper  350  is closely received during and after closing, with the first and second edges  354 , 356  being proximate the guide wall inside surface  376 , 378 , while the flapper&#39;s forward edge  358  is proximate the pin  260  in pin hole  314 . Such proximity to the guide wall inside surfaces  376 , 378  provides lateral resistance to any lateral movement and/or deformation of the flapper  350 . In some exemplary embodiments the pins  260  are constructed from 4140 or 4340 alloy steel and the flapper  250  is constructed from cast iron bar stock, including heat treated ductile iron having approximately 115,000/130,000 psi (792,897/896318 kPa) tensile strength, approximately 76,000/85,000 psi (524001/586054 kPa) yield strength, and an approximately 4 percent elongation rating. 
         [0108]    Turning now to  FIGS. 51-55 , wherein an exemplary embodiment  400  of the present invention is shown to have, a tubular housing assembly  410  having a tubular housing  420  having an interior pocket  422  with an inside surface  424 . The tubular housing is threadably attached to a top member (“top sub”)  426  having a bottom end  428 , a top end  430  with threads  432  usable for attachment to a downhole tubular assembly component, such as a casing joint pin. Threads  429  are provided on the lower exterior of the top sub. The top sub  426  attachment to the tubular housing is sealed using conventional O-rings in O-ring grooves  433   a,b  in the top sub  426 . The tubular housing  420  is further threadably attached to a bottom member (“bottom sub”)  440  having a top end  442 , forming an upwardly facing shoulder  444  adjacent the interior pocket an interior surface  424 , and a bottom end  446  with threads  448  usable for attachment to a downhole tubular assembly component, such as a casing collar. The bottom sub  440  attachment to the tubular housing is sealed using O-rings in O-ring grooves  449   a,b  in the bottom sub  440 . The bottom sub  440  further has interior threads  452  for receiving flapper seat threads  453  in such a manner that the flapper seat  302  is secured within the tubular housing  420 . This attachment does not interfere with the removeability and/or interchangeability of the bottom sub  440 , such that the bottom sub may be chosen to match the downhole tubular assembly component that is otherwise being used in the well. 
         [0109]    The tubular housing  420  also has interior threads  456  for threadable attachment of the top sub  426  using threads  429 . The tubular housing also has four (two shown) circumferentially spaced holes  458   a,b  for positioning four (two shown) shear members, i.e. screws  460   a,b  for retaining the sleeve  90  in its original position against the flapper seat  300  with the flapper  350  in the open position. 
         [0110]    Turning now to  FIG. 56 , wherein is depicted an exemplary embodiment  500  of an insert assembly of the present invention, wherein structure substantially similar to the pinned guide walls  372 , 374  is integrated into the flapper seat  502  during original manufacture, eliminating the need to pin additional structure on the flapper seat. 
         [0111]    Turning now to  FIG. 57 , wherein an exemplary embodiment  600  of the present invention is depicted and shown to include a flapper seat elevation  604  encompassing the flapper on three sides, and having a bevel  606 , directed inwardly toward the interior of the flapper seat  602 ) to guide the flapper  350  within, i.e. partially encompassed by, the elevation as it moves to the down position. The elevation functionally replaces the five pins  260 , discussed above in other exemplary embodiments, and resists and/or substantially prevents lateral movement of the flapper  350  toward the front edge  608  or side edges  610 ,  612  of the flapper seat  602  in response to pressure on the flapper curved surface. In some exemplary embodiments, the elevation is separated into two or more sections, for example, two side portions and one front portion. 
         [0112]    All equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. The descriptions in this specification are for purposes of illustration only and are not to be construed in a limiting sense.