Abstract:
A ball catcher is adapted to be fluidly connected to a wellhead port to receive wellbore fluids and balls carried therewith. A diverter is fit to the catcher body and has a wellhead end positioned to intercept the fluid flow from the wellhead port so as to divert debris and balls carried therein into a ball recovery chamber. The diverter has a bore in fluid communication with the flow outlet and the wellhead end has flow passages formed therethrough to the bore for receiving the fluid flow free of debris and balls and discharging the fluid flow from the catcher body. The diverter and the ball recovery chamber can be connected to quick removal for replacement, repair or cleaning.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a regular application claiming priority of U.S. Provisional Patent Application Ser. No. 60/945,989 filed on Jun. 25, 2007, the entirety of which is incorporated herein by reference for all purposes. 

   FIELD OF THE INVENTION 
   This invention relates generally to apparatus and method for the retrieval of balls from a wellbore, such as drop balls, frac balls, packer balls and other balls for interacting with downhole tools in the wellbore. The balls are recovered with the fluid stream which flows from the wellbore, such as after stimulation operations. More particularly, the apparatus and method uses apparatus affixed to the wellhead for intercepting, separating or diverting the balls from the fluid flow for recovery. 
   BACKGROUND OF THE INVENTION 
   It is known to conduct fracturing or other treating procedures in a wellbore by isolating zones in the wellbore using packers and the like and subjecting the isolated zone to treatment fluids at treatment pressures. In a typical fracturing procedure, for example, the casing of the well is perforated to admit oil and/or gas from the formation into the well and fracturing fluid is then pumped into the well and through these perforations into the formation. Such treatment opens and/or enlarges draining channels in the formation, enhancing the producing ability of the well. Alternatively, the completion can be an open hole type that is completed without Casing in the producing formation area. 
   It is desired to stimulate multiple zones, or intervals within the same zone, using onsite stimulation fluid pumping equipment (pumpers). A packer arrangement is inserted at intervals isolating one zone from an adjacent zone. It is known to introduce a drop ball through the wellbore to engage one of the packers in order to block fluid flow therethrough. Passage through a downhole packer is thereby plugged off with this drop ball that is pumped into the wellbore during the stimulation flush. The drop ball blocks off this downhole packer, isolating the wellbore uphole of the downhole packer and consequently a second zone, above this downhole packer, can be stimulated. Once stimulated, a subsequent drop ball can be dropped to block off a subsequent packer uphole of the blocked packer for stimulation thereabove. This continues until all the desired zones are stimulated. 
   At surface, the wellbore is generally furnished with a frachead unit including a multi-port block or a Y-type frac header, isolation tool or the like, which provides fluid connections for introducing stimulation fluids including sand, gels and acid treatments. 
   After the well operations, fluid from the well is flowed to surface through the wellhead or frachead. The fluid is urged from the well such as under formation pressures and/or the influence of a gaseous charge of CO 2  or N 2 . The fluid from the well exits the wellhead from a horizontally extending fitting. To separate the balls from the fluid, it is known to use a cross fitting apparatus such as a plate extending across the flow path from the wellhead. The plate is typically a plate across the flow path having large slots or screen at the face such as an upside down “U” or fork shape for impeding balls recovered with the fluid while permitting fluid to flow therethrough the “U” shape 
   It is known for balls, of which various sizes are employed in one well operation, to become lodged at the prior art U-shape or screen and block fluid flow. In other instances, the balls can break apart which encourages further blockages. 
   There is a need for a more effective apparatus for retrieving balls from a wellbore after a well operation. 
   SUMMARY OF THE INVENTION 
   Embodiments of the present invention intercept and divert balls returning with wellbore fluid into a ball recovery reservoir. A ball catcher body includes a replaceable diverter which separates balls and debris from the fluid flow. 
   In one aspect of the invention, apparatus is provided for retrieving oversize debris and balls carried with a fluid flow from a wellhead port. A catcher body is adapted to be fluidly connected to the wellhead port and has a flow outlet. A diverter is fit to the catcher body and has a wellhead end positioned to intercept the fluid flow from the wellhead port so as to divert debris and balls carried therein into a ball recovery chamber. The diverter has a wellhead end has flow passages formed therethrough for receiving the fluid flow free of debris and balls. The diverter has a bore in fluid communication with the flow outlet. Fluid flow through the flow passages enters the bore for discharge from the catcher body. 
   In another aspect of the invention, the catcher body is connected and positioned along a fluid flow path from the wellhead. The catcher body has a first flow path contiguous with fluid flow from the wellhead and an intersecting stagnant ball recovery reservoir. The catcher body has a catcher flow outlet for fluid free of debris and balls. The debris and balls have a first velocity vector along the flow path towards the catcher flow outlet. A diverter, fit to the catcher body and having a wellhead end extending into the flow path intercepts the fluid flow. The diverter has a bore being open at a tail end and in fluid communication with the catcher flow outlet. The diverter has a diverter face at the wellhead end and being positioned inline with the first velocity vector for intercepting and substantially arresting the debris and balls and for diverting the debris and balls along into the ball recovery reservoir. An annular chamber formed in the discharge outlet about the wellhead end of the diverter receives the fluid flow. A plurality of flow passages extending through the wellhead end of the diverter conduct fluid flow, free of debris and balls, from the annular chamber to the bore for discharge through the tail end. 
   As a result, a reliable and easy to clean ball catcher is provided for servicing wells after stimulation and cleaning operations such as after drilling removal of bridge plugs and the like. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a wellhead of conventional configuration fit with a flow port such as a frachead and a ball catcher according to one embodiment of the invention; 
       FIG. 2  is a cross section of a ball catcher body according to one embodiment of the invention fit to a flow port of a wellhead illustrating the sequential movement of a ball carried out of a wellbore with fluid flow to divert for recovery in the ball recovery reservoir; 
       FIG. 3A  is a side cross-sectional view of an embodiment of a ball diverter; 
       FIGS. 3B and 3C  are face and partial top views of the diverter of  FIG. 3A  along the lines I-I and II-II respectively; 
       FIG. 4  is a partial cross-sectional close up view of the diverter of  FIG. 4  installed in the ball catcher body; 
       FIGS. 5A ,  5 B,  5 C,  5 D and  5 E are cross-sectional views of various embodiments of a diverter; 
       FIG. 6  is a cross-section of an alternate embodiment of a ball catcher body and illustrating a diverter accordingly to  FIG. 5E ; and 
       FIG. 7  is a cross-sectional view of a wellhead of conventional configuration fit with a first ball catcher and showing a second ball catcher for connection to the wellhead according to another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIG. 1 , in the context of fracturing a formation traversed by a wellbore and recovering fluid therefrom, a wellhead  10  is connected to the wellbore (not shown) for introducing fracturing fluid and drop balls for various operations to the wellbore. The wellhead comprises a shutoff valve  11  and a flow port  12  thereabove, typically integrated with a frachead. Thereafter a fluid flow F carrying debris and drop balls B are flowed out of the well through the flow port along a fluid path  13 . While a variety of materials such as frac sand are carried out of the wellbore with the fluid flow, for the purposes of simplicity herein, this application discusses the apparatus and operations in the context of the recovery of balls. 
   With reference to  FIG. 2 , an embodiment of a ball catcher  20  is adapted to be connected to the wellhead&#39;s flow port  12 , such as through an isolation valve  14 , for catching drop balls B before they travel downstream and adversely affect other equipment. 
   As shown, the ball catcher  20  comprises a catcher body  21  fit to the wellhead  10  or isolation valve  14  at a wellhead connection using industry approved threaded or flanged connections. The catcher body  21  further comprises a stagnant reservoir or ball recovery chamber  22  which intersects the fluid path  13 . Fluid flow F flows along a first velocity vector or fluid path  13  and is interrupted with a diverter  23  fit to a catcher flow outlet  24 . The fluid flow F carries the balls to impact the diverter, separating fluid flow F and the balls B for discharge of the fluid flow from the catcher flow outlet  24  and recovery of the balls at the ball recovery chamber  22 . 
   With reference also to  FIGS. 3A-3C , the diverter  23  has a wellhead end  30  for intercepting the fluid flow F and a diverter body  31  fluidly sealed, such as by an O-ring  29 , to the catcher flow outlet  24 . The diverter body  31  has bore  32  and a fluid discharge or tail end  33 . The bore  32  is open at the tail end  33  and in fluid communication with the catcher flow outlet  24  for the collection and discharge of fluid flow F liberated of oversize solids such as the balls B. The wellhead end  30  of the diverter  23  projects into the fluid path  13  and comprises a diverter face  34  positioned in the fluid path  13 . The diverter face  34  is positioned inline with the first velocity vector for intercepting and substantially arresting the debris and balls B and for diverting the debris and balls along into the ball recovery chamber  22 . 
   Referring also to  FIG. 2 , kinetic energy in balls B is dissipated at the diverter face  34  and the balls fall under gravity into the ball recovery chamber  22 . The ball recovery chamber  22  is intersects and fluidly contiguous with, but diverges from, the flow path  13 . As shown, the flow path can be substantially horizontal from the wellhead  10  and ball recovery chamber  22  is positioned below the diverter face  34 . The diverter face  34  can be angled downward, from top to bottom and away from the fluid path  13 , for directing, deflecting or urging the balls downward into the ball recovery chamber  22 . A cross-sectional dimension of the diverter face  34  can be substantially the diameter of that of the flow path  13 . Best seen in  FIG. 3 , the diverter face  34  can have a concave face having an axis oriented generally downwards towards the ball recovery chamber  22 . 
   With reference to  FIG. 4 , the diverter face  34  diverts oversize solids, such as debris or balls B. 
   In one embodiment, the diverter face  34  diverts a portion or all of the fluid flow F therearound. An annular chamber  40  is formed in the catcher body  21  or catcher flow outlet  24  about the wellhead end  30  of the diverter  23 . The annular chamber  40  receives fluid flow F continuing to flow substantially along the flow path  13  and about the diverter face  34 . The fluid flow F flows through the annular chamber  40  and inward through flow passages  41  formed or extending through the wellhead end  30 . The bore  32  receives fluid flow F free of debris and balls for discharging the fluid flow from the catcher body. 
   With reference to  FIGS. 5A-5C , the diverter  23  can be removeably fit to the catcher body, similar to a cartridge, for ease of replacing the wear components. The diverter body  31  can be one piece  31   s , as shown in  FIG. 5C , or two or more pieces  31   m , as shown in  FIGS. 5A and 5B . A two-piece body  31   m  permits the most wear prone portion, the wellhead end  30 , being separable from the tail end  33 . The wellhead end  30  could be manufactured of wear resistant material. Alternatively, the flow passageways  41  are wear resistant, being coated with wear resistant material or be manufactured using replaceable, hardened orifices (not shown). The wellhead end  30  comprises the diverter face  34  and the flow passages  41  for conducting fluid flow F to the bore  32 . The wellhead end  30  of a two-piece diverter body  31   m  has a threaded pin portion  42  and fluid seal  43  for sealing to a box end  44  of the tail end  33 . The tail end  33  has a second fluid seal, such as the O-ring  29 , for sealing to the catcher body  21 . 
   As shown in  FIG. 4 , the diverter body  31  can be cylindrical for insertion into the catcher flow outlet  24  and secured or retained therein by quick connection such as a coupling  50  and hammer nut  51 . The diverter can also be retained using a flanged or similar connection (not shown). The coupling  50  can be threadably engaged with the diverter&#39;s tail end  33 . Replacement of the diverter can be effected by equalizing fluid pressure in the catcher body  21 , releasing the hammer nut  51  and replacing the entire diverter body  31  or replacing a worn wellhead end  30  of a two-piece diverter body  31   m.    
   The flow passages  41  can be radial flow passages  41  or extend substantially in-line with the flow path  13 . As shown in  FIGS. 5A-5C  and  5 E, some flow passages  41  though the wellhead end  30  can be radial, extending to the bore  32 . Further, the flow passages  41  can be oriented radially and opposingly positioned to neutralize fluid energy as the fluid flow F enters the diverter bore  32 . The plurality of flow passages can be arranged in pairs of opposing flow passages  41   p  for directing fluid flow F to impinge each other within the bore  32  and dissipate energy to minimize erosion. 
   The flow passages  41  in the diverter are sized to pass the fluid flow F and can be oversized to accommodate accumulative loss due to plugging. Further, the fluid passages can be sized to be large ( FIGS. 5B ,  5 C and  5 E) for passing a range of particulates to the downstream equipment. In another embodiment, the fluid passages can be small ( FIGS. 5A and 5D ) for blocking the passage of large particulates for the protection of the downstream equipment, the large particulates being collected instead in the ball recovery chamber  22 . A plurality of small flow passages  41 , such as those shown in  FIG. 5A , can act as screen to reject undesirable particulates. Similarly, a cylindrical screen could be fit over larger flow ports. 
   For example, with reference to the embodiment of  FIG. 4 , eight flow passages  41  arranged in four pairs  41   p , positioned at quadrants, at ⅛″ diameter each can pass 5-7 m 3  (per hour) of fluid (such as water or lighter hydrocarbons). Eight flow ports at 5/32″ diameter can (each) pass 9-11 m 3 /hour and ¼″ ports can (each) pass 20-25 m 3  (per hour). The greater the number of flow passages passing the return fluid, the less the erosion, thus increasing the life and efficiency of the diverter or diverter cartridge. 
   With reference to  FIG. 6 , in another embodiment, the diverter  23  can further comprise in-line flow ports through the diverter face  34  and oriented into the fluid path  13 . The in-line flow passages are smaller in diameter than are the solids or balls B being rejected and collected in the ball recovery chamber  22 . 
   Operation 
   As shown in the embodiments shown in  FIG. 2 , upon establishing fluid flow F from the wellbore, balls B (and other debris) engage the diverter face  34  and are collected in the ball recovery chamber  22 . Fluid flow F continues downstream, passes through the diverter&#39;s flow passages and is discharged through the diverter&#39;s tail end  33  to other equipment as is the usual practice in the industry. 
   Periodically, the wellhead  10  is shut in and a bleed valve  60 , such as positioned atop the catcher body  21 , is vented to equalize pressure therein and the ball recovery chamber  22  can be emptied of debris and balls B. The diverter  23  can be quickly inspected and replaced as necessary, therefore decreasing the down time in flow back procedures. The ball recovery reservoir can further comprise a pup joint  55  coupled releaseably to the ball recovery chamber  22  using quick connect couplings  56 . In another embodiment the wellhead  10  can be isolated from a catcher body  21  and fluid from the downstream equipment can be backflowed through the diverter  23  and ball recovery chamber  22  for cleaning. 
   With reference to  FIG. 7 , a second ball catcher  20 B, or more depending upon the wellhead, can be fit to the wellhead  10  of  FIG. 1 , also with isolation valving  14 , 14  between the wellhead  10  and each of the ball catchers  20 , 20 B. Accordingly, the first ball catcher  20  can be serviced, for replacement of the diverter  23  or inspection and cleaning of the chamber  22 , while the second ball catcher  20 B is in operation. In this way, wellhead flow is not interrupted. In some wellbores, even a temporary interruption can result in an unfavorable loss of suspended materials which are being elutriated from the wellbore with the fluid flow. Accordingly, redundant ball catchers  20 , 20 B are affixed to two or more flow paths  13  from the wellhead so that fluid flow F from the wellbore can be substantially continuous to the second ball catcher  20 B while the first ball catcher  20  is taken out of service. 
   Undesirable sand plugs or debris plugs can occur from the fallout and or the formation may lose its upward energy and die which requires expensive coil tubing to clean the well pipe. Also flowback disruption during coil clean out, or for example bridge plug mill out, needs to be avoided because the fallout can create a sand plug and jam around the coil tubing causing further and significant expense. The second ball catcher  20 B can be opened for operation, both being used temporarily, before closing in the first catcher for servicing. 
   In another embodiment shown in  FIG. 6 , an isolation valve  62  can be provided to optionally temporarily block the ball recovery chamber  22  from the catcher body  21  for servicing. Further, a purge port  63  can be provided to introduce nitrogen to purge the ball recovery reservoir of noxious gases such as hydrogen sulphide.