Abstract:
The invention comprises a tool for launching objects downhole, such as one or more plugs in a desired sequence. The movements leading to the release of the individual plugs are regulated by virtue of displacement of oil through at least one orifice. The wiper plugs are retained in the tool until such time as they are physically displaced beyond the lower end of the tool. The biased retainers holding the plugs within the tools are released upon a predetermined movement of the plugs beyond the lower end of the tool. If the retaining mechanism for the plug does not automatically release upon sufficient extension of the wiper plug from the tool, a pressure assist can be used to launch any given plug. The darts used to move an actuating piston to release the plugs are separated from the plugs and retained in the tool so that they do not need to be drilled out later.

Description:
FIELD OF THE INVENTION 
     The field of this invention relates to launching objects downhole, particularly wiper plugs used in cementing of tubulars downhole. 
     BACKGROUND OF THE INVENTION 
     Currently available designs for launching plugs downhole employ a variety of mechanical retention devices for sequential release of plugs. These devices are typically collets or a variety of shearable devices intended to sequentially release wiper plugs into a liner ahead of the cement and behind it. Typically, these devices are attached at the bottom of the liner setting tool. After the liner is properly hung, the tool is called upon to sequentially launch the wipers to facilitate the cementing of the liner through a cementing shoe. Typical of such products is the LFC four-plug system, product No.  269-27  made by Baker Oil Tools. In this device, a series of darts of different sizes engage different sized wiper plugs to pry them loose from the connection mechanism. The dart goes down with the wiper plug and must be drilled out later. A shock loading is placed on the retention mechanism as the dart lands in its respective plug. While there are many variations of these wiper plug-launching systems, the nature of the retention devices used for the wiper plugs has in the past caused some operational difficulties in a variety of different ways. In some situations, the wiper plugs would not release at all. In other situations, more than one wiper plug released when only one was intended to be released. Darts used to launch the plugs had to be drilled out. 
     Typically in these systems, after landing the first wiper plug, a barrier through or around the plug is broken to allow pumping of the cement before pushing the next plug down behind the cement. Plugs with breakable barriers for this purpose have been used in the past. These plugs are also typically made of soft materials so that they can be quickly drilled out after the cementing operation is concluded. Typical of such plugs are those illustrated in U.S. Pat. Nos. 5,435,386; 5,361,835; and 5,311,940. 
     It is an object of this invention to provide a reliable apparatus for launching objects downhole, particularly wiper plugs in the proper sequence with confidence. In describing and claiming the invention, references to “wiper plugs” or “plug” are intended to be broad enough to include any other objects such as “balls,” as one example. This objective is accomplished by regulated movement of the various components to avoid abrupt movements due to pressure buildups normally used in delivery of wiper plugs where darts land in them in order to launch. The objective is further met by a sequential operation which can effectively launch one or a plurality of plugs in a desired sequence. Provisions are made for a pressure-assisted shear release as an emergency technique for release of the wiper plug in the event it does not automatically release for any reason. These and other objectives of the invention will become more readily understandable to one of skill in the art from a review of the preferred embodiment described below. 
     SUMMARY OF THE INVENTION 
     The invention comprises a tool for launching objects downhole, such as one or more plugs in a desired sequence. The movements leading to the release of the individual plugs are regulated by virtue of displacement of oil through at least one orifice. The wiper plugs are retained in the tool until such time as they are physically displaced beyond the lower end of the tool. The biased retainers holding the plugs within the tools are released upon a predetermined movement of the plugs beyond the lower end of the tool. If the retaining mechanism for the plug does not automatically release upon sufficient extension of the wiper plug from the tool, a pressure assist can be used to launch any given plug. The darts used to move an actuating piston to release the plugs are separated from the plugs and retained in the tool so that they do not need to be drilled out later. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a-g  show a sectional view of the tool upon attaining the desired position with a ball dropped to obstruct a port in an actuating sleeve. 
     FIGS. 2 a-g  show the actuating sleeve shifted, breaking a rupture disc in the tool. 
     FIGS. 3 a-g  show the launching of the dart to obstruct a lateral port at the conclusion of the initial movement of the actuating sleeve. 
     FIGS. 4 a-g  show the first wiper plug released out the bottom of the tool after further shifting of the actuating sleeve. 
     FIGS. 5 a-g  illustrate the first wiper plug going to the cementing shoe, followed by cement from an exposed lateral opening in the tool. 
     FIGS. 6 a-g  illustrate the dropping of a second dart, obstructing the lateral opening in the tool. 
     FIGS. 7 a-g  illustrate further shifting of the actuating sleeve by pressure on the second dart to release the second wiper plug after cementing has concluded. 
     FIGS. 8 a-h  illustrate the second wiper plug being released from the tool and landing on the first wiper plug near the cementing shoe. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 a-g , the plug-launching tool T has a top sub  10  with a thread  12 . Connected above thread  12  and not shown in the figures is the hanger mechanism for hanging the liner to the tubular through which it has just been run. The liner  14  is the one to be cemented using the tool T. Connected to the top sub  10  is body  16 . Thread  18  connects body  16  to top sub  10 . A bottom sub  20  (see FIG. 1 d ) is connected to body  16  at thread  22 . Attached to bottom sub  20  by virtue of thread  26  is a sleeve  24 . Sleeve  24  encloses wiper plugs  28  and  30  during run-in. Wiper plug  28  is attached to wiper plug  30  by virtue of pin  32  extending into groove  34 , which is built into wiper plug  30 . Pin  32  is biased inwardly by spring  36  but, in the position shown in FIG. 1 e , cannot come out of groove  34  because of sleeve  24 . Similarly, wiper plug  30  has a pin  38  biased inwardly by a spring  40 . Sleeve  24  holds the pin  38  in a groove  42  in end connection  44 , which is in turn secured to shaft  46  at thread  48 . At the upper end of shaft  46 , an actuating piston  50  is secured at thread  52 . 
     Defined between shaft  46  and body  16  are sealed cavities  54 ,  56 , and  58 . Cavity  54  is sealed off by seals  60  and  62  at its lower end, respectively, against body  16  and shaft  46 . Cavity  54  has an outlet port  64  which is obstructed by a “rupture disc,” which is defined as any device which can obstruct the path and then open it after a predetermined pressure, chemical or other triggering event or signal is applied. In the preferred embodiment, a rupture disc  65  is employed in passage  64  so as to give good control of the predetermined pressure that needs to be applied before rupture disc  65  breaks to allow an incompressible fluid such as, for example, mineral oil, which is in cavity  54 , to be pushed out of the tool T through filter  51  and replaceable orifice  67 . After breakage, the size of the opening left by the broken rupture disc or the diameter of passage  64 , or the opening in replaceable orifice  67 , can serve as the flow restrictor for the mineral oil in cavities  54 ,  56  and  58 . This flow restriction regulates movement of piston  50  to avoid putting pressure shocks on the formation. The upper end of the cavity  54  is defined by movable piston  66 , which has peripheral seals  68  and  69  and a thru path  70 , which is obstructed by a rupture disc  72 . Again, as in the case with rupture disc  65  and with all the other “rupture discs” to be described in the preferred embodiment, other devices which block off a bore until a predetermined condition occurs, whereupon the bore is opened up. The preferred breakpoint for rupture disc  72  is lower than rupture disc  65 . Since each floating piston  66  and  74  is in pressure balance until rupture disc  65  breaks, the set pressure of rupture disc  65  can be higher than rupture discs  72  and  80 , and rupture disc  65  will break first. Cavity  56  is defined between piston  66  and movable piston  74 . Piston  74  has peripheral seals  76  and  77  and a bore  78 , in initially obstructed by rupture disc  80 . Rupture disc  80  is preferably set to break at the same pressure as the pressure required to break rupture disc  72 . This is because rupture disc  80  is in pressure balance until rupture disc  72  is broken. Cavity  56  is filled with mineral oil or any other suitable incompressible fluid. Displacement of the oil acts as a fluid damper on the actuating piston  50 . Finally, cavity  58  is defined between piston  74  and actuating piston  50  and is sealed off by seal  80  against the body  16 . 
     Referring to FIGS. 1 a  and  b , the actuating piston  50  has a ball seat  82  to accept a ball  84  to apply pressure in passage  86 . In order to allow the ball  84  to be pumped down to seat  82 , an opening  88  in actuating piston  50  is aligned with lateral port  90  in top sub  10  so that fluid can pass around the tool T and deliver the ball  84  to the seat  82 . Annular gap  94  allows the fluid to bypass the tool T after emerging from port  90 . Pressuring on ball  84  sets a liner hanger (not shown) and releases a running tool (not shown) and shifts actuating piston  50  without releasing wiper plug  28 . 
     Referring again to FIGS. 1 e  and  f , it can be seen that the wiper plugs  28  and  30  have been pushed into sleeve  24  with their wiping elements  95  and  96  compressed. The wiper plug  28  has a pair of O-rings  98  and  100  which seal in bore  102  (see FIG. 8 h ) when the wiper plug  28  is caught on its shoulder  104 . This occurs near the cementing shoe (not shown) which is just below stop ring  106  shown in FIG. 8 h . Referring again to FIGS. 1 e-f , it can be seen that the wiper plug  28  has a breakable barrier  108  which again can be a rupture disc or any other assembly which opens up passage  110  in wiper  28  at a predetermined applied differential pressure or other condition. 
     Sleeve  24  also includes a passage  112  which allows the space above plug  28  to fill with wellbore fluids at the pressure for the depth where the tool T is found to avoid collapse of sleeve  24  due to trapped atmospheric pressure internally. 
     The wiper plug  30  has an elongated seal  114  of the type described in U.S. Pat. No. 5,611,547. Seal  114  generally sees higher differential pressures than seals  98  and  100 . Accordingly, seal  114  is uniquely configured to deal with high differential pressures and temperatures which could be seen downhole. A large port  116  is in sleeve  24  above wiper plug  30 . The purpose of this port is to prevent collapse of sleeve  24  due to differential pressures resulting from any trapped atmospheric pressure liquid in cavity  118 . With the passage  116 , cavity  118  is at the surrounding wellbore pressures and flow can come in to cavity  118  as the plugs  28  and  30  are displaced out of sleeve  24 . 
     The principal components of the plug-launching tool T having been described, its operation will now be described in more detail. As shown in FIG. 1, the initial step is to pump ball  84  down against seat  82  to allow pressure in passage  86  to shift the actuating piston  50 . This same pressure buildup sets the liner hanger (not shown) and releases the running tool (not shown). Pressure applied to actuating piston  50  increases the pressure in cavities  54 ,  56 , and  58 . Again recalling that pistons  66  and  74  are floating, the applied pressure due to attempt to move the actuating piston  50  downwardly results in an increase in pressure behind rupture disc  65  which is in outlet port  64 . Eventually, the rupture disc  65  breaks (after the liner hanger, not shown, sets), allowing the fluid-filled cavity  54  to decrease in volume as its contents are slowly pushed through the ruptured disc  65  and orifice  67 . As fluid is displaced out of cavity  54  allowing its volume to decrease at a regulated rate due to the size of the orifice  67 , the actuating piston  50 , along with the shaft  46  connected thereto, moves the wiper plugs  28  and  30  at a controlled rate to the position shown in FIGS. 2 d-f . At this time, pin  32  is still retained in sleeve  24 . However, the movement of the wiper plugs  28  and  30  has been gradual. In the position of FIGS. 2 d-f , wiper plug  28  is still retained within sleeve  24  and retained to wiper plug  30 . 
     Referring to FIGS. 3 a  and  b , a dart  120 , having a seal  122 , is pumped into contact with actuating piston  50 . This can happen because the movement of actuating piston  50 , shown in FIG. 2 b , has left port  90  exposed due to the top of actuating piston  50  moving past it. Thus, dart  120  again obstructs passage  86 , allowing for further pressure buildup which will move dart  120  and actuating piston  50  in tandem. When the pressure is increased in passage  86 , the pressure is further increased to the point where rupture disc  72  in the now-shifted piston  66 , will break because it now can see a pressure difference in view of breakage of rupture disc  65  and piston  66  hitting its travel stop. It should be noted that breaking of rupture disc  65 , coupled with a reduction in volume of cavity  54 , has been accomplished by displacing piston  66  to the position shown in FIG. 2 d . In any event, a buildup in pressure above dart  120  in passage  86  will result in breakage of rupture disc  72  and displacement at a controlled rate of fluid from cavity  56 , whose volume will now decrease as floating piston  74  is to be displaced toward piston  66 , which has now bottomed against bottom sub  20 . Thus, FIGS. 3 a-f  illustrate the onset of pressure buildup which breaks rupture disc  72 , while in FIGS. 4 a-f , the assembly including the dart  120 , actuating piston  50 , shaft  46 , and wiper plugs  28  and  30 , have all shifted downwardly. At this point, as shown in FIGS. 4 f-g , wiper plug  28  is now below the sleeve  24 , allowing the inward bias of spring  36  on the pin  32  to be overcome as pressure forces pin  32  out of groove  34 , overcoming the bias of spring  36 . As the wiper plug  28  emerges from sleeve  24 , the wiping elements  95  spring outwardly to seal off against the liner  14 . In a position shown in FIG. 4 f , the wiper plug  28  is in the position for imminent release, which is shown more clearly in FIG. 5 g . The difference between FIGS. 4 and 5 is that in FIG. 5, the movable piston  74  has concluded its movement and bottomed on piston  66 . As shown in FIG. 5 g , the wiper plug  28  is now clear of sleeve  24  and is launched in advance of cement or other sealing material which can now be pumped through passage  86  through port  90 , which is again exposed when dart  120  clears seal  122  past port  90 . Surface personnel will know that the wiper plug  28  has been launched when they see a sudden decrease in pressure as seal  122  of dart  120  moves past port  90 . The same kind of signal will also be seen when actuating sleeve  50  has been pushed sufficiently far to break rupture disc  65 . This will occur because of a sudden pressure decrease as seal  92  of the actuating sleeve  50  clears past port  90 , as shown by comparing FIGS. 1 a  and  b  with FIGS. 2 a  and  b.    
     It should be noted that any mechanism that releases upon movement of the plugs  28  and  30  is within the scope of the invention. Sleeve  24  can have an internal ramped recess which will release a plug  28  even before it fully clears sleeve  24 . Pins can move to the bottom of a slot at which point they shear off, releasing the plug. As long as the movement is regulated, a variety of release techniques that actuate with movement can be used. 
     Accordingly, at the conclusion of the steps shown in FIG. 5, the wiper plug  28  has been successfully launched and is now being displaced downhole ahead of the cement or other sealing material which is being pumped through passage  86  and port  90 . Eventually, as shown in FIG. 8 h , the wiper plug  28  lands in bore  102  of stop ring  106 . At this time the pressure buildup of the pumped cement will break the barrier  108  to allow the cement to proceed through the cementing shoe and up around the outside of the liner  14  to cement it. It should be noted that at this time the wiper plug  30  is not yet in position, and those skilled in the art will appreciate that FIG. 8 h  is the final position after cementing is concluded and wiper plug  30  is launched, as will be described below. However, for continuity as to the positioning of wiper plug  28 , its ultimate position downhole is referred to at this time by directing the reader&#39;s attention to FIG. 8 h.    
     To conclude the cementing operation, it is desired to launch the wiper plug  30  from its retained position within sleeve  24  to displace cement from the liner. A second dart  124 , shown in FIG. 6, is dropped on top of the first dart  120 . Again, this obstructs the port  90  by virtue of seal  126 . Pressure applied to passage  86  displaces the actuating piston  50  and breaks the rupture disc  80  in piston  74 . When rupture disc  80  breaks, the volume of cavity  58  can be reduced, which in turn allows the shaft  46 , driven by actuating piston  50 , to push the wiper plug  30  beyond sleeve  24 . Again, the process is repeated as pin  38  is forced out of groove  42  against the bias of spring  40  by pressure from uphole. The wiping elements  96  expand to obstruct the inside diameter of liner  14 . The downward movement of wiper plug  30  terminates as shown in FIG. 8 h  when it hits wiper plug  28 . At this time, the seal  114  is in bore  102  and all of the cement pumped ahead of wiper plug  30  is now displaced around the cementing shoe and around the outside of liner  14 . It should be noted that the wiping elements  96  do not enter into bore  102  of stop ring  106 , but may seal internally in liner  14 . The main seal, however, for the wiper plug  30  is the bullet seal  114 . 
     If for any reason the wiper plug  28  when in the position of FIG. 4 f  does not release, pressure applied in passage  86  when port  90  is ultimately exposed will act on the now-expanded wiper elements  95  such that the force put on the wiper plug  28  will either shear the pin  32  or instead, shear a portion  128  of the wiper plug  30  which presents immediately below the groove  34 . In either event, by application of sufficient fluid force to the wiper plug  28 , if it hasn&#39;t already released when extended out of sleeve  24 , a release can still be accomplished as a backup measure should the pin  32  fail to clear groove  34 . A similar technique can be applied to wiper plug  30  if, in the position shown in FIG. 7 f , it still fails to release from groove  42 . 
     Those skilled in the art will appreciate that any number of wiper plugs, such as  28  and  30 , can be launched from the plug-launching tool T. The successive of movements required to launch additional wiper plugs can be accommodated with the addition of further movable pistons, such as  66  and  74 , so that additional steps of movement can be coordinated from the surface by virtue of dropping additional darts, such as  120  and  124 , to conclude the additional movements necessary to put any number of plugs outside the sleeve  24  in a desired sequence. All the darts are retained in the tool and are not launched with a wiper plug. In that way they do not have to be drilled out after cementing. 
     The advantage of the rupture disc  65  is that all the movements can occur at predetermined pressures and will occur fairly gradually as the rate of expulsion of fluid through the outlet port  64  can be regulated by virtue of either an orifice  67  in port  64 , or a broken rupture disc  65 , or the size of port  64  itself. Surface personnel can more easily tell what is happening since movements downhole are intended to occur at particular applied pressures. Thus, surface personnel can see through pressure changes at the surface that the requisite next move of the tool T downhole has occurred. With the use of rupture discs  72  and  80 , each of the desired steps occurs at predetermined pressures, while the rate that each step is accomplished is regulated through the ability of the displaced fluid to escape through the opening provided by a broken rupture disc  65 . The formation is not shocked by sudden movements and the apparatus works more smoothly due to its gradual movements. The design is compact by employing an elongated series of cavities which ultimately communicate with each other through the breakage of rupture discs located in movable pistons. The actuation of the plugs using darts now involves a separation by way of the actuating piston so that the darts can be retained and the movement which releases the plugs can be controlled. While the preferred embodiment is for dropping wiper plugs, any object that can fall downhole can be launched with the disclosed apparatus. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.