Abstract:
A tool for dropping one or more balls and then one or more darts features a closable ball drop opening that works automatically after the ball release to minimize damage to the subsequently released dart. A retainer keeps the darts from coming back up above the dart launcher in the event of a pressure surge in the well. The dart launcher features a dedicated movable barrel for each dart that can be locked in a fully misaligned and fully aligned position with the casing or tubular. A handle is retained to the dart housing and can be manipulated to defeat the lock and rotate a given barrel. The darts may be inspected in their respective barrels before launch and the launch order is variable.

Description:
PRIORITY INFORMATION 
   This application claims the benefit of U.S. Provisional Application No. 60/591,058, filed on Jul. 26, 2004. 

   FIELD OF THE INVENTION 
   The field of this invention related to surface cementing heads for dropping balls and wiper plugs into a wellbore. 
   BACKGROUND OF THE INVENTION 
   In cementing casing or liners the procedure typically involves dropping one or more balls for engagement with a downhole seat sized for that ball to allow pressure buildup to set downhole devices such as external casing packers. After the ball is dropped and the downhole equipment is set, the delivery of the cement occurs in conjunction of delivery of one or more wiper plugs or darts down the casing. These plugs separate mud from cement or clean the inside of the casing. 
   Typically the ball-dropping device is located below the dart-releasing device so that the darts must travel past the ball-releasing device after it has dropped the balls. One problem with this layout is that the ball dropping device, after release of the ball, presents either a large opening or edges that can engage the trailing cups on the dart as it is pumped by. What has happened is that tears can develop in these cups allowing fluid bypass around the dart. This can stop the forward motion of the dart or impede its ability to separate fluids or to clean the inside wall of the casing or tubular as it is forced downhole. Accordingly, as described below with regard to the preferred embodiment, as solution to this problem has been devised to try to minimize the tendency to tear the darts as they pass the ball release device. 
   In another aspect, a provision is made to prevent the darts from coming back uphole, in the event of a pressure surge. Such darts are retained from traveling above their release mechanism. The release mechanism for the darts features, in the preferred embodiment, individual release barrels for each dart allowing for the darts to be dropped in any order. It further allows observation of what dart is in which barrel without affecting the operation of the other barrels holding other darts. Each barrel is movable between a fully misaligned and fully aligned position with the casing or tubular and can be locked in at least two positions. A handle assembly stays with the dart dropping unit and manipulation of the integrated operating handle acts to defeat the lock and rotate a barrel into an aligned position with the casing for launch of the dart. 
   U.S. Pat. No. 6,182,752 shows a tool that drops darts by continuing rotation in a fixed direction requiring a predetermined order of dropping once the darts are loaded and no provision for checking which dart is in which barrel after loading. 
   The above described advantages and other features of the invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the claims, which appear below. 
   SUMMARY OF THE INVENTION 
   A tool for dropping one or more balls and then one or more darts features a closable ball drop opening that works automatically after the ball release to minimize damage to the subsequently released dart. A retainer keeps the darts from coming back up above the dart launcher in the event of a pressure surge in the well. The dart launcher features a dedicated movable barrel for each dart that can be locked in a fully misaligned and fully aligned position with the casing or tubular. A handle is retained to the dart housing and can be manipulated to defeat the lock and rotate a given barrel. The darts may be inspected in their respective barrels before launch and the launch order is variable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevation view of the assembly showing the dart dropping housing above the ball dropping housing; 
       FIG. 2  is a section view of a ball trapped in the dropper before release; 
       FIG. 3  is the view of  FIG. 2  showing the door opened and the ball having been released; 
       FIG. 4  shows the door to the casing closed before the darts are dropped; 
       FIG. 5  is the view along line  5 - 5  of  FIG. 1 ; 
       FIG. 6  is the view along line  6 - 6  of  FIG. 1 ; and 
       FIG. 7  is an enlarged view of the dart dropper showing the lock and handle feature. 
       FIG. 7   a  is a view along lines  7 - 7  of  FIG. 7  with the handle extended out fully vertically and then rotated into a perpendicular horizontal plane. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , the plug or dart dropping housing  10  is mounted above the ball dropping housing  12 . While one of each is illustrated those skilled in the art will appreciate that more than one of each can be used. The housing  12  is shown in greater detail in  FIGS. 2-4 .  FIG. 4  will be used to describe the components of the housing  12 . A handle  14  is mounted for 360 degree rotation of a cam  16 . The handle  14  is secured by a pin  18  to cam  16 . The casing or tubular  20  has an interior wall  22 . A door  24  has a curved surface  26  designed to approximate the curvature of the interior wall  22  of the casing  20  when in the position shown in  FIG. 4 . The cam  16  has a guide rod  28  that extends into the door  24 . A spring  30  surrounds rod  28  to bias the door  24  into a position where curved surface  26  is positioned as close as possible to the interior wall  22 . Door  24  has an upper tapered surface  32  to ease its travel path up the outside wall  34  of the casing  20  when the handle  14  is rotated 180 degrees from the position shown in  FIG. 4 . The door  24  moves in tandem with the cam  16  because pin  28  secures the door  24  to the cam  16 . 
   The operation is best understood by going back to  FIG. 2 . There a ball  36  is loaded and retained in a space  37  by an extension  38  of the plug  16 . Note that rod  28  extends into extension  38  for tandem movement. A curved ramp  41  can be seen in the out of contact position from the ball  36  when the handle  14  is pointing left in  FIG. 2 . As the handle  14  is rotated, the extension  38  takes rod  28  with it forcing the ramp  32  up the outside wall  34  of the casing  20  and up against the bias of spring  30  that surrounds rod  28 . 
   The movement of handle  14  180 degrees to the  FIG. 3  position takes door  24  away from opening  42  in the casing  20  allowing the curved ramp  41  to push the ball  36  through opening  42  and allow it to fall or be pumped downhole through casing  20 . 
   After release of ball  36 , the handle  14  is rotated another 180 degrees in either direction to allow door  24  to be again aligned with opening  42  and to allow the spring  30  to bias door  24  so that its curved surface  26  stays as closely aligned as possible with the inner wall  22 . In this position it is selectively locked as shown schematically as  15  in  FIG. 4 . What will happen next is that a plug or dart will be dropped from housing  10 . Because the door  24  with its curved surface  26  now sits in actual or near alignment with interior wall  22 , there is a reduced chance of damage to the plug or dart  44  as it clears housing  12 . The dart typically has one or more cups for sealing against the wall  22  of the casing  20  to allow it to be easily pumped down. These cups have caught on openings, sharp edges or ledges presented by the ball droppers of the prior designs and the result has been damage or destruction of the cups on the dart  44 . The assembly described above with door  24  addresses this issue by closing the opening  42  after the ball is released and in a manner that minimizes pinch points that can damage the dart  44  that is subsequently dropped past opening  42 . 
     FIG. 6  illustrates that housing  10  can have mirror image ball dropping assemblies each having a door  24  that works in the above described manner and closes with surface  26  as nearly flush as possible with the interior surface  22  of the casing  20  so as to minimize subsequent damage to the dart  44 . While reference has been made to a ball  36  those skilled in the art will appreciate that other shapes can be used and that fluid pressure rather than curved ramp  41  can be used to get the ball  36  out. 
   Referring now to  FIGS. 6 and 7 , the details of the dart dropping housing  10  will be explained. Housing  12  has a central bore  45 . For illustrative purposes, there are three barrels  46 ,  48  and  50  that are each independently rotatable into or out of alignment with bore  45  and two of which  46  and  48  are shown in  FIG. 7 . Each barrel can be locked in either position and features an integral handle assembly that can defeat the lock to facilitate rotation. An open barrier  52  is within the inner wall  22  that continues below as part of the casing  20 , as shown in  FIG. 4 . This barrier keeps the darts  44  from going further up beyond housing  10  in the event of a pressure surge in the well. At the same time, because barrier  52  is open, flow can pass through it to allow pumping the dart  44  down the casing  20 .  FIG. 5  shows the operating shaft assemblies  54 ,  56  and  58  that respectively operate barrels  46 ,  48  and  50 . One shaft assembly will be described in detail, as in the preferred embodiment they are all identical. A lower shaft  60  is linked (preferably by meshing gears, not shown) or via arms  61  and  63  for rotation of a barrel such as  46  about an arc  49  as shown in  FIG. 5 . Similarly, barrels  48  and  50  are respectively independently rotated about arcs  47  and  51  by their operators  56  and  54 . An upper shaft  62  is keyed to lower shaft  60  at connection  64 . A handle  66  is screwed to bolt  68  in the stowed position. A ball  70  at the lower end of handle  66  keeps the handle within cap  72  after the handle is unthreaded from bolt  68  and lifted away from bolt  68  up to the point where ball  70  is stopped by travel stop  75 . A dog  74  extends into a groove  76  in upper shaft  62 . When the handle  66  is pulled away from bolt  68  until ball  70  stops further outward travel of the handle  66 , the handle  66  is rotated to a position perpendicular to axis  63  while still retained by the shaft  62  to engage the dog  74  to cam it away from groove  76  along mating tapers  78 . While still engaged by shaft  62 , the handle can rotate about axis  63  in an opening  73 , see  FIG. 7   a , that is sufficiently wide to allow handle  66  to rotate shaft  62  well under 60 degrees to align or misalign a barrel such as  46  with the central bore  45 .  FIG. 7   a  has been added to show the handle pulled all the way up along axis  63  and turned to a plane perpendicular to axis  63  and then rotatable in that plane perpendicular to axis  63  to align a barrel in the passage  45 . The bell  70  can be unthreaded from  68  and raised straight up inside shaft  62  along axis  63 . The opening  77  on top of cap  72  is smaller than the receptacle  70  preventing it from coming straight out of shaft  62  along axis  63 . When the handle is fully extended along axis  63  until it hits opening  77  in cap  72 , the handle can be turned 90 degrees into gap  73  in the side of cap  72 . In the position of  FIG. 7   a  the handle  66  can turn left or right as shown by arrows  79 . Since the top of shaft  62  is also slotted in alignment with slot  73 , the left or right movement  79  of handle  66  will turn shaft  62  and  60  which move in tandem. Handle  66  is not removable from shaft  62 . At this point dog  74  snaps into another groove  76  to lock the barrel  46  in the position of alignment with bore  45 . An indicator  80  of a type known in the art signals the passage of dart  44  out of barrel  46 . The other darts  44  in the other barrels  48  and  50  can then be released in the same way, after barrel  46  is retracted out of alignment with bore  45 . 
   This arrangement offers advantages over prior dart dropping designs. One is that each barrel can be inspected to be sure there is a dart  44  in it before the cementing procedure starts. The darts  44  can then be dropped in any desired order. The handle  66  that operates an individual barrel cannot be lost as it is made to be retained by the cap  72 . Any of the barrels can be selectively locked in the drop position where there is alignment with bore  45 . The locking is automatic upon rotation into position and dog  74  falling into slot  76  when barrel  46  aligns with bore  45 , for example. By manipulating the handle, after dropping the dart  44  the dog is retracted allowing the reverse movement to occur to fully misalign barrel  46  from bore  45  and lock that position as dog  74  falls into another slot (not shown) on cap  72 . Again the other barrels preferably work in the same manner. 
   While three barrels in one housing  10  are shown, varying numbers of barrels can be used in each housing. Shafts  60  and  62  can be in one piece and can also be power driven as opposed to manual handle  66 . 
   Using the combination of equipment described above, one or more objects of the same or different dimensions can be dropped from housing  12  followed by closure of the opening or openings  42  with a door  24  to present a flush or nearly flush surface  26  adjacent the inner wall  22  of the casing  20 . The darts  44  can then be dropped in any order from a given housing  10  with little concern about damage as they pass openings  42  that are covered with a door  24  that is flush or nearly so. If there is a pressure surge as the darts are being dropped, the barrier  52  prevents them from being blown past the housing  10 . The built in handle  66  can&#39;t be lost. The barrels  46 ,  48  and  50  can be selectively locked in a fully aligned position with bore  45  or in a fully misaligned position or any other desired position. The dog  74  engages a groove such as  76  automatically and can be defeated by permitted movements of the handle  66  within cap  72 . 
   While the preferred embodiment has been set forth above, those skilled in art will appreciate that the scope of the invention is significantly broader and as outlined in the claims which appear below.