Patent Publication Number: US-2002007950-A1

Title: Valves

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates to improvements in valves. In particular, but not exclusively, the invention relates to an improved downhole valve.  
       BACKGROUND OF THE INVENTION  
       [0002] In oil and gas exploration and production, subsurface hydrocarbon-bearing formations are accessed by drilled bores extending from surface. The bores are lined with metal casing, and the bores of production wells normally accommodate at least one tubing string for carrying production fluid to the surface. The casing and the tubing often feature valves to control the flow of fluid through the bore. Two forms of valve are in common use in these applications: ball valves and flapper valves. Ball valves generally provide an effective seal, but restrict the available bore area. Flapper valves typically allow provision of a larger area bore but tend to be more difficult to seal, particularly in the case of curved flapper valves; the curved form is preferred as it minimises the loss of bore area when the valve is open. Further, flapper valves tend to be more sensitive to debris and other material collecting on a closed valve, which may then prevent the valve from opening or from opening fully.  
       [0003] It is among the objectives of embodiments of the present invention to provide an improved valve which obviates or mitigates some of the disadvantages of conventional ball and flapper valves.  
       SUMMARY OF THE INVENTION  
       [0004] According to the present invention there is provided a valve comprising: a body defining a through bore and a valve seat; and a valve member mounted in the body and moveable between positions to open and close the body bore, the valve member defining a portion of a surface of a sphere, in the open position the valve member being located to one side of the bore and in the closed position the valve member surface engaging the valve seat.  
       [0005] The provision of a valve member of this form provides for a degree of flexibility in the location of the valve member in the closed position, while still maintaining an effective seal between the valve member and the valve seat; even if the valve member is rotated from its preferred closed position the form of the valve surface in contact with the valve seat, that is a part-spherical surface, remains the same. Such flexibility is not available in conventional curved flapper valves, in which even a limited degree of movement of the valve member relative to its seat is likely to result in a loss of sealing. Further, as the valve member defines only a portion of a sphere surface, the member occupies a smaller volume than a corresponding ball valve, thus facilitating provision of a larger area bore through the open valve.  
       [0006] Preferably, the valve member defines a segment of a wall of a hollow sphere. One or both of the part-spherical upper and lower surfaces of such a valve member may be adapted for cooperating with valve seats.  
       [0007] Preferably, the valve is a downhole valve, adapted for location in downhole tubulars such as casing, liner, drill pipe or production tubing.  
       [0008] Preferably, the valve member is movable between the closed and open positions along a path corresponding to the surface of said sphere; in effect, the valve member is rotated about an axis of the sphere. The effective axis of rotation may lie within the body, either on or spaced from the centre line of the body bore, in which case the valve member may be pivotally mounted to the body. Most preferably however, the effective axis of rotation lies outwith the body, such that the curvature of the valve member may be reduced, and thus the depth of the valve member may also be reduced, minimising the cross sectional area occupied by the valve member in the open position.  
       [0009] Preferably, the valve body defines a valve member-receiving volume, adapted to be occupied by the valve member in the open position, and having at least an inner wall corresponding substantially to the form of the adjacent face of the open valve member. Thus, there will tend to be a minimum of void space surrounding the valve member in the open position. However, a void, in the form of a “tonsure”, may be provided to accommodate debris which is carried into the volume on the valve member opening. Due to the form of the valve member, and the manner in which the member is translated between the open and closed positions, the body may be substantially thicker at this point than a conventional valve body, increasing the ability of the valve body to withstand elevated pressures.  
       [0010] Preferably also, the valve seat is movable relative to the valve member. Most preferably, the valve seat is adapted to be urged towards the valve member, to maintain seal integrity therebetween. The seat may be arranged such that fluid pressure in the body bore tends to urge the seat towards the member, for example by provision of a differential piston arrangement on the seat.  
       [0011] Preferably also, two valve seats are provided, one on each side of the valve member, such that the valve is capable of holding pressure from both sides. Of course, a valve capable of holding pressure from both sides may also be provided with only a single valve seat, provided that the seat itself is sealed to the valve body. The form of the valve member allows the member to slide between the seats, into the closed position.  
       [0012] The valve member may be pivotally mounted to the body or may be slidable relative to the body. In the latter case, the valve may further comprise a curved track along which the valve member is movable. The valve member may be actuated to move between the open and closed positions by any convenient means, including an electric motor, a physical link to a remote power source or prime mover, or pressure forces transmitted by fluid in control lines, or via a bore or bore annulus. Where the valve member is slidable relative to the body, the valve member may be conveniently actuated via a flexible member capable of transmitting a compressive force, such as a push chain, examples of which are manufactured by Franz Morat KG of Eisenbach, Germany.  
       [0013] According to another aspect of the present invention there is provided a valve comprising:  
       [0014] a body defining a through bore; and  
       [0015] a valve member mounted in the body and being moveable along a curved path between open and closed positions, the path corresponding to an arc of a circle having its centre located outwith the body.  
       [0016] Of course the entire path between the open and closed positions of the valve member need not necessarily be curved, or correspond or approximate to such an arc, for example in some valves it may be convenient to include a substantially straight path portion.  
       [0017] The valve may provided integrally with a section of tubing, that is, for example, a section of casing may form a pressure housing for the valve. Alternatively, the valve may have a discrete pressure housing and may be adapted, for example, to be run into existing casing. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0018] These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
     [0019]FIG. 1 is a rear view of a valve in accordance with an embodiment of a first aspect of the present invention;  
     [0020]FIG. 2 is a sectional view on line A-A of FIG. 1;  
     [0021]FIG. 3 is a sectional view on line B-B of FIG. 2;  
     [0022]FIG. 4 is a schematic perspective view of part of a valve, including a lower valve body and valve member, in accordance with an embodiment of another aspect of the present invention; and  
     [0023]FIG. 5 is a schematic perspective view of an upper valve body for the valve of FIG. 4. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
     [0024] Reference is first made to FIGS.  1  to  3  of the drawings which illustrate a valve  10  in accordance with an embodiment of a first aspect of the present invention. The valve  10  is intended to be located in a tubing string for location in a drilled bore and comprises a body  12  defining a through bore  14  and upper and lower valve seats  16 ,  17  (FIG. 2). A valve member  18  is mounted to the body  12 , the valve member  18  defining a segment of a wall of a hollow sphere. Pivot arms  20 ,  21  extend from the sides of the member  18  and engage respective pivot pins  22 ,  23  on the body  12 . The common axis of the pivot pins  22 ,  23 , and thus the pivot axis of the valve member  18 , is perpendicular to and intersects an axis of the circular section body bore  14 . The valve member  18  may be pivoted from an open position, as illustrated in the Figures, to a closed position in which the valve member  18  closes the bore  14 . In the open position, the valve member  18  is located outwith the bore wall  24 , but within the circumference of the generally cylindrical body  12 . Thus, in order to accommodate the valve member  18 , the bore  14  is offset within the body  12 , that is the main axes of the body  12  and the bore  14  are spaced apart.  
     [0025] The bore wall  24  defines a gap  26  to allow the valve member  18  to move through the wall between the open position and the closed position, in which the valve member  18  extends across the bore  14 . The valve member  18  may be rotated between the open and closed positions by any convenient means, as will be apparent to those of skill in the art.  
     [0026] When closed, the valve will hold pressure from both above and below, and the valve seats  16 ,  17  are arranged such that an elevated pressure on one side of the closed valve member  18  tends to urge the respective valve seat  16 ,  17  into contact with the valve member surface.  
     [0027] Reference is now made to FIGS. 4 and 5 of the drawings, which are schematic illustrations of elements of a valve  30  in accordance with an embodiment of another aspect of the present invention. The valve  30  includes a two-part body  32  (FIG. 4),  33  (FIG. 5) defining a through bore  34  having a centre line offset from the centre line of the body, and upper and lower valve seats  36  (only lower seat shown). A valve member  38  is mounted to the lower body  32  via a T-shaped key  40 , extending from the upper end of the valve member  38 , and located in a corresponding curved undercut slot  42  in the body wall. The slot  42  follows an arc of a circle having its centre outwith the body  32 . Further, the valve member  38  is in the form of a segment of the wall of a hollow sphere with a corresponding centre, such that the upper and lower valve member faces which provide contact with the valve seats are concave partspherical and convex part-spherical, respectively.  
     [0028] The parts of the body  32 ,  33  cooperate to define a volume adapted to receive the valve member  38  when the valve  30  is open. As the valve member  38  is translated along a curved path of a radius corresponding to the radius of the member  38 , the valve member-receiving volume may be relatively shallow, and only slightly deeper than the thickness of the valve member  38 . Indeed, in this embodiment the outer face of the body  44  which defines the inner wall of the valve member-receiving volume is substantially part-spherical. Thus, advantageously, the wall of the body  46  may be relatively thick in this area. Clearly, the thicker portions of the body wall  46  offer increased resistance to failure or deformation due to exposure to elevated internal pressure, and furthermore the thicker portions  46  serve to reinforce and support the adjacent, thinner wall portion  48 .  
     [0029] The spacing between the valve member  38  and the body  33  is selected to accommodate some debris, as may gather on the upper face of the closed member  38 . In particular, a circular tonsure  50  is provided on the body face  44 .  
     [0030]FIG. 4 shows the valve  10  in the open configuration, and the valve is closed by pushing the valve member  38  downwardly along the slot  42 , and between the valve seats  36 , such that the member  38  extends across the bore  34 . The member  38  may be actuated between the open and closed positions by any suitable means, as will be apparent to those of skill in the art.  
     [0031] Those of skill in the art will note that the above-described valve forms offer many of the advantages of a flapper valve, in that the provision of the valve does not result in a significant restriction in the available bore diameter. Further, the part-spherical form of the valve members  18 ,  38  facilitate formation of a fluid tight seal between the valve seats and the valve member surfaces, both above and below the valve member, such that the valve arrangement is ideally suited to applications in which it is desired to accommodate pressure both above and below the valve. The ability to obtain a seal between the valve member and the valve seats is enhanced as a degree of rotation of the valve member relative to the seats may be accommodated without any change in the shape of the valve member surfaces which are in contact with the valve seats. This contrasts with conventional curved flappers, in which even a minor misalignment between the valve member and the valve seats will likely prevent formation of a seal. The manner in which the valve member moves between the closed and opened positions also facilitates opening of the valve when debris has gathered on the upper face of the closed valve member: the sliding movement of the valve member through an opening in the bore wall tends to push any debris from the valve member, in contrast to a conventional flapper in which debris can be trapped between the opening flapper and the valve body, thus preventing the flapper pivoting fully upwards to the closed position. The embodiment of FIGS. 4 and 5 also provides the advantage of a relatively robust yet compact valve body.  
     [0032] It will also be apparent to those of skill in the art that the above-described embodiments are merely exemplary of the invention, and that various modifications and improvements may be made thereto, without departing from the scope of the present invention. For example, it is not essential that the entire valve member is part-spherical in form: only one face of the member may be part-spherical, or only a valve seat-engaging annular area of one or both major surfaces of the member may be part-spherical.