Abstract:
The problem of flappers that will not close due to high velocity gas rushing past and creating a vortex that has zones of high pressure pressing the flapper against the force of the torsion spring is reduced or overcome with modifications in the passage through a subsurface safety valve so as to reduce the intensity of the vortex to allow the torsion spring to pivot the flapper to closed position. Various shapes are inserted adjacent the flapper base to create turbulence to minimize or prevent the vortex and the associated pressure increases that would otherwise prevent flapper closure with the flow tube retracted. Inserts that create turbulence are placed in a recess that in part holds the flapper when it is rotated to the open position.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is subterranean safety valves of the flapper type and more particularly vortex control features that allow the flapper to close in high velocity fluid flow applications. 
       BACKGROUND OF THE INVENTION 
       [0002]    Subsurface safety valves generally have a flapper that is closed by a torsion spring that is mounted on a pivot pin for the flapper. A hydraulic control system actuates a piston to move a flow tube in the valve passage against the flapper to hold it open. If pressure in the hydraulic system is removed or lost, the closure spring acts on the flow tube to lift it away from the flapper that until that time had been behind the flow tube in a recess in the housing. Once the flow tube moves up the torsion spring in the flapper pivot shaft would do the work of starting rotational movement of the flapper toward its conforming seat. When the flapper contacted the seat the pressure of the fluid below kept the flapper in that closed position sealed against the flapper seat. Pressurizing the control system again brought the flow tube against the closed flapper and made it pivot off the seat back to the open position. 
         [0003]    As safety valves were made with larger flow bores and dealt with higher velocities particularly in gas service transient vortexes were formed of high pressure zones that changed location depending on the velocity. At certain flow passage dimensions and flow velocities these high pressure zones occurred in front of an open flapper to create a sufficient hold open force that the torsion spring was unable to move the flapper to the closed position even after the flow tube was raised to allow such flapper movement. 
         [0004]    In the past, in addressing the larger sized flapper safety valves and the limitations of the torsion spring to move an ever heavier flapper, designs were developed along the lines of providing an assist to the torsion spring to start the flapper moving toward the closed position when the flow tube was raised up. U.S. Pat. No. 6,227,299 used a leaf spring  122  located behind the flapper  86  to add a closing force. US Publication 2009/0151924 uses a shape memory alloy closure spring to get a boost in the flapper closing force. Going in the opposite direction, U.S. Pat. No. 7,703,532 holds the flapper open with movably mounted magnets and U.S. Pat. No. 7,270,191 provides a mechanism to open the flapper when it will not go from the closed to the open position with the hydraulic system. US Publication 2009/0032238 uses repelling magnets in the housing and the flapper to give an assist to a torsion spring on the flapper pivot pin. U.S. Pat. No. 7,448,219 is a hingeless flapper design that shapes the flapper to be aerodynamic so that it can operate responsive to the flow passing by in an automotive application. U.S. Pat. No. 7,644,732 uses a bypass technique for dealing with pressure surges in a lubrication system when the circulating oil is still cold. 
         [0005]    The various solutions discussed above have in common a focus on adding a closing force when it is time for the flapper to go to the closed position. The present invention addresses the configuration of the flow passage to reduce or eliminate the effect of flow induced pressure transients that can overcome the ability of the flapper torsion spring to close it in high velocity fluid flow situations in the order of 300 feet per second or higher. Rather than adding to the mechanical closing force applied to the flapper, the present invention focuses on dissipation of flow induced moving pressure gradients that can act on the flapper at the time it needs to close and reducing their affects by shaping the profile of the flow passage in the vicinity of the flapper or the flapper itself so that the localized pressure differentials are not large enough to overcome the torsion spring trying to close the flapper. Those and other aspects of the present invention will become more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is provided by the appended claims. 
       SUMMARY OF THE INVENTION 
       [0006]    The problem of flappers that will not close due to high velocity gas rushing past and creating a vortex that has zones of high pressure pressing the flapper against the force of the torsion spring is reduced or overcome with modifications in the passage through a subsurface safety valve so as to reduce the intensity of the vortex to allow the torsion spring to pivot the flapper to closed position. Various shapes are inserted adjacent the flapper base to create turbulence to minimize or prevent the vortex and the associated pressure increases that would otherwise prevent flapper closure with the flow tube retracted. Inserts that create turbulence are placed in a recess that in part holds the flapper when it is rotated to the open position. Additionally and alternatively the flapper itself can be machined so as to create a larger annular space behind the flapper when it is open so that some part of the generated vortex can be used to push the flapper to the closed position and to offset the high pressure zones created on the other side of the open flapper. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a prior art view of a flapper in the open position even after the flow tube moves uphole and flow passing through the passage that holds the flapper open due to a vortex causing high pressure; 
           [0008]      FIG. 2A  schematically shows the vortex against the flapper to hold it open; 
           [0009]      FIG. 2B  illustrates the vortex shown in  FIG. 2A  and the high velocity flow passing straight through as the flapper is held open; 
           [0010]      FIG. 3  shows one form of a device to reduce the pressure in the vortex using a partial sleeve that comes to a point directed at the incoming flow and has opposed sides sloping away from the leading point; 
           [0011]      FIG. 4  puts an insert in the groove where the flapper is located when it is open showing a series of transverse ridges; and 
           [0012]      FIG. 5  shows an insert member in the groove where the flapper is located in the open position where the insert has an internal open space. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    As an introduction to the issue addressed by the invention  FIG. 1  illustrates a tubular string  10  that has a safety valve housing  12  secured to the string  10  at opposite ends  14  and  16 . In the position of  FIG. 1  the flow tube (not shown) has already been raised by a control system (not shown). Normally, the raising of the flow tube allows a torsion spring  20  about a pivot shaft  18  to apply its stored potential energy force and rotate the flapper  22  toward a schematically illustrated seat  24 . All the components of the housing  12  are not shown to add clarity to the identification of the issue using  FIG. 1 . Arrow  26  represents the incoming high velocity stream that is most likely to be gaseous and in the order of about 300 feet per second or higher to cause the problem. Flow lines  28  graphically illustrate how most of the flow goes straight through the housing  12  in a direction toward the surface. However, depending on the velocity and the composition of the passing fluid some of the flow begins to ebb into the recess  30  and create a vortex  32  generally that begins away from the location of the flapper  22  and works its way around the housing  12  in the recess  30 . The vortex creates a high pressure concentration that is shiftable with the velocity that passes through the housing  12 . In the beginning as the velocity picks up the vortex  32  is located near the lower end  34  of the flapper  22 . At that location, the vortex  32  can actually be an aid to closure of the flapper  22  as it can pass through the gap  36  between the inside of the recess  30  and the housing  12 . Once reaching the small annular space  38  defined by the tapered surface  40  on flapper  22  and the housing  12 , the presence of the higher pressure at location  38  helps push the flapper away from wall  42 . However as the velocity increases and the center of the higher pressure vortex  32  moves closer to the surface and toward the pivot shaft  18  the moment balance shifts and there is an ever greater moment acting on the top side  44  of the flapper that can be easily in excess of the closing moment applied by the torsion spring  20  as aided by what remaining portions of the vortex  32  still in the vicinity of the gap  36 . 
         [0014]      FIG. 2A  adds to the schematic representation of how the vortex  32  works its way circumferentially to the top surface  44  of the flapper  22 .  FIG. 2B  is the same illustration as  FIG. 2A  but showing a different viewing angle for more of a perspective view. Should the velocity at the time the flow tube is raised in an effort to have the torsion spring  20  rotate the flapper  22  to a closed position against its seat  24 , the result can be that there is no flapper  22  movement at all. This can defeat the operation of the safety valve and can cause a blowout that would otherwise be prevented by the proper operation of the safety valve. 
         [0015]    There are several ways that this situation can be addressed and three variations are illustrated in  FIGS. 3-5  as preferred without any intent on limiting the variety of the approaches that look to reconfigure the internal passage in the housing  12  or the relation of the passage  44  to the flapper  22  or/and shaping of the flapper so that the vortex  32  is minimized in its intensity to the point where the torsion spring  20  can close the flapper  22 ′ as needed or in the ideal case prevent the vortex  32  from forming at all. In  FIG. 3  the shoulder  46  and the flapper base  48  define the recess  30 ′ between them. Since the view in  FIG. 3  is in section, only one half of the insert  50  is illustrated. The balance of the insert  50  that is not shown is preferably the mirror image of what is depicted. As a result the shape forms a downhole oriented point that can be sharp or blunt  52  from which opposed sides  54  extend and diverge in a direction toward the surface. The flow direction is given by arrow  56 . The thickness of the insert  50  as well as its shape can be optimized using Computational Flow Dynamics software that can create a three dimensional model of the flow regime through the passage  44 . Thus the height of the insert  50  can be varied to be taller, shorter or about the same height as the shoulder  46  that defines the recess  30 ′. 
         [0016]    In a variation of the  FIG. 3  design the insert  50  can be shaped to be a cylindrical member that fills partially to totally that portion of the recess  30 ′ that continues beyond the sides of the flapper  22 ′ so that in essence the circumferential extent of the recess  30 ′ is somewhat wider that the width of the flapper  22 ′ and that is it. Alternatively the flapper base  48  can be extended to accomplish the same result in a one piece rather than a two piece construction. 
         [0017]    Another option is shown in  FIG. 4  where the insert  58  is similarly positioned as in  FIG. 3  and this time has a series of ridges such as  60  and  62  that are transverse to the direction of flow  64  that would otherwise cause the vortex  32  to form. The number and height and orientation of the ridges can also be optimized for the expected flow velocities. There can be ridge combinations that are transverse as shown in  FIG. 4  combined with some ridges that are closer to parallel to the flow direction. A surface roughening on the face of the insert that faces the passage  44  is another alternative to control the vortex  32 ′. 
         [0018]    Another approach is seen in  FIG. 5  where the insert  65  has a void  66  that in the  FIG. 5  is illustrated as square. Here again as in  FIGS. 3 and 4  what is shown is a part of the insert  64  without the mirror image of it that is not in the illustration. Here again the void shape can be varied and optimized by mathematical modeling. There are other options for vortex control that can be implemented. For one the width of the gap  36  can be varied. Another approach is to increase the volume of the space behind the flapper and the surrounding housing. One example is to machine grooves on the back side of the flapper that faces the wall  42 ′ such as schematically illustrated by the dashed line  68 . There is a limit to the extent that the grooves on the back of the flapper can be used especially in the larger sizes as the flapper has to take large pressure differentials when closed and adding grooves can promote flapper distortion under maximum working pressure differentials to the point where leakage can occur. The idea on the back of the flapper is to create empty space behind the flapper to enable the vortex  32  to get into that space and add a closing moment that can help the torsion spring close the flapper. 
         [0019]    It should also be noted that as the velocity increases the vortex  32  moves closer to the pivot shaft  18  and has a much smaller moment arm in the high pressure zone that it creates. That is one reason that the various inserts of  FIGS. 3-5  end at the flapper base  48 . Optionally there can be a gap between the insert of any of the illustrated configurations or others that can be developed with mathematical modeling and the flapper base. 
         [0020]    Another option to get an assist to the flapper  22 ′ is illustrated in  FIG. 3 . A passage or passages  70  can start at passage  44  at a location  72  that is above the shoulder  76  where the flow tube  77  lands when the valve is in the open position. When the vortex  32  is centered on the flapper  22 ′, the tubing pressure in the passage  44  can be communicated to the zone behind the flapper  22 ′ at  74 . The passage  70  can be run as shown in  FIG. 3  or it can use an external jumper if the passage from location  72  is run to the exterior face  79  and then jumpered to the outer face and into a lateral bore of the housing  81  in behind the flapper  22 ′. 
         [0021]    While the illustrated valve is shown as operated with a flow tube  77  other designs using flappers that operate without a flow tube are also contemplated. Such devices can be powered by magnetic or other force fields to move the flapper between the open and closed positions. 
         [0022]    The above description is illustrative of the preferred embodiment and various alternatives and is not intended to embody the broadest scope of the invention, which is determined from the claims appended below, and properly given their full scope literally and equivalently.