Abstract:
A wiper plug release tool uses a first pump down plug that lands in the tool to pressurize an internal chamber to slide a sleeve that undermines a set of dogs to allow the lower wiper plug to be decoupled from support. The shifting of this sleeve cams a second set of dogs into an internal passage in the tool to act as a landing location for a second pump down plug. Landing the second pump down plug on the now extended dogs allows a net pressure to be applied to an upper piston which shifts a sleeve to release the support for the second wiper plug. The upper piston remains in pressure balance unless the second pump down plug can be landed on the dogs that only extended because the sleeve that released the lower wiper plug had shifted.

Description:
FIELD OF THE INVENTION 
     The field of this invention is wiper plug dropping tools and more particularly those that can sequentially launch wiper plugs using pump down plugs that are retained in the tool. 
     BACKGROUND OF THE INVENTION 
     In cementing casing or liner, wiper plugs are used to isolate the delivered cement from existing well fluids and to drive any leftover cement out of the casing or liner and through the cement shoe, which is a one way valve at the lower end of the casing or liner string. Some systems get by with only a single wiper plug. In those systems the cement is delivered on top of existing well fluids with no barrier. After the cement is delivered, the one wiper plug is dropped to displace the cement from the casing or liner and into the surrounding annulus. After that the cement shoe at the bottom of the string along with the wiper plug are simply milled up and the well is continued deeper. 
     In two wiper plug systems of the past, one of the concerns was to only drop one wiper plug at a time. Earlier designs of multi-plug systems used a system of two shear pins. The lower pin supported the lower wiper plug from the wiper plug above it. The upper pin held the upper plug to the tool body and was designed to shear at a higher pressure than the lower shear pin. A pump down plug seated in the tool to allow pressure to break the lower shear pin while claiming to keep the upper wiper plug in pressure balance. What was supposed to happen is that the lower pin sheared and the lower wiper plug launched. Then another pump down plug was landed to allow a net pressure force to be applied to the remaining wiper plug so that the upper shear pin that was rated higher than the lower shear pin could release. The upper wiper plug then was launched. This design is illustrated in Application WO 94/27026. The problem with this design is that if the lower shear pin didn&#39;t release when needed, pressure would build to the point of breaking the higher set upper shear pin and both wiper plugs would launch together. In other words, there was nothing to assure the upper wiper plug could not be launched with the lower wiper plug. 
     In an effort to address this issue U.S. Pat. No. 6,206,094 was designed to use a hydraulic system with metering capability to advance the lower wiper plug while it was still retained to the tool for a given travel distance at which point the lower wiper plug could launch. A first pump down plug allowed pressure to be applied to move a piston that moved the wiper plug at a controlled rate until it extended far enough from the tool housing to be released. A second pump down plug then allowed another piston to move at a regulated rate to advance the second wiper plug beyond the housing far enough so that it too could be launched. While this tool provided greater assurance of launching only one wiper plug at a time, it was complicated and involved rupture discs and hydraulic flow through metering orifices. It presented some risk for smooth operation as intended. 
     Other known wiper plug launching systems were the LFC Four Plug System offered by Baker Oil Tools that worked similarly to Application WO 94/27026 but used collets which became unsupported or sheared to trigger a release in conjunction with shear pins to hold a sleeve from moving where a collet became unsupported for release. Another similar design is U.S. Pat. No. 5,553,667 (FIG. 9). Other designs in this area include U.S. Pat. Nos. 5,803,173; 6,712,152; 6,698,513; 6,575,238; 6,681,860; 6,672,384 and 7,055,611. 
     What is needed and provided by the present invention is a wiper plug dropping tool that retains the pump down plugs and ensures the orderly release of the wiper plugs. It features a sleeve that is moved to release the lower wiper plug whose movement makes it possible to actually land another pump down plug in a proper position so that the release mechanism for the upper wiper plug can be actuated. Without movement of the release sleeve for the lower wiper plug there is no release of the upper wiper plug. These and other features of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings with the understanding that the full scope of the invention is measured by the claims that appear below. 
     SUMMARY OF THE INVENTION 
     A wiper plug release tool uses a first pump down plug that lands in the tool to pressurize an internal chamber to slide a sleeve that undermines a set of dogs to allow the lower wiper plug to be decoupled from support. The shifting of this sleeve cams a second set of dogs into an internal passage in the tool to act as a landing location for a second pump down plug. Landing the second pump down plug on the now extended dogs allows a net pressure to be applied to an upper piston which shifts a sleeve to release the support for the second wiper plug. The upper piston remains in pressure balance unless the second pump down plug can be landed on the dogs that only extended because the sleeve that released the lower wiper plug had shifted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a - 1   d  show a half section of the tool in the run in position; 
         FIGS. 2   a - 2   d  show the tool of  FIGS. 1   a - 1   d  with the first pump down plug landed; 
         FIGS. 3   a - 3   d  show the tool of  FIGS. 2   a - 2   d  with lower wiper plug released; 
         FIGS. 4   a - 4   d  show the tool of  FIGS. 3   a - 3   d  with the second pump down plug landed and the upper wiper plug released to drop; 
         FIGS. 5   a - 5   d  show the tool of  FIGS. 4   a - 4   d  with the upper release sleeve locked into the released position; 
         FIG. 6  is the view along lines  6 - 6  of  FIG. 1   b ; and 
         FIGS. 7   a - 7   b  show both launched wiper plugs captured in a landing collar downhole. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1   a  upper mandrel  10  has a thread  12  for connecting a string, not shown. A rupture disc  14  allows diversion of pressure from internal passage  16  to the annulus  18 , for an emergency procedure that will be described below. The surrounding casing or liner that defines the annulus  18  is not shown except as  20  in  FIG. 7 , which is at the lower portion of the string to be cemented and generally close to a cementing shoe (not shown). 
     A port  22  leads from passage  16  into chamber  24  that is defined by outer sleeve  26 . Port  28  is offset from port  22  and is isolated by sleeve  30  and its seals  32  and  34 . Sleeve  30  is secured between upper mandrel  10  and lower mandrel  52 . Seal  38  spans the gap between upper mandrel  10  and sleeve  30 . Seal  40  seals between mandrel  10  and sleeve  26  on the other side of port  22  so that when pressure is applied through passage  22  with passage  16  obstructed, as will be explained below, pressure builds up in chamber  24  to put uphole pressure on sleeve  26 . Sleeve  26  carries a snap ring  42  that is designed to snap into surface  44  after uphole movement of sleeve  26 . The snapped in position is shown if  FIG. 5   a . Concluding the description of the sleeve  26  a lower segment  46  attached at thread  48  and having a lower end  50  with an internal recess  51 . 
     Continuing now with the upper mandrel  10 , a lower mandrel  52  is attached at thread  54  trapping a sleeve  56  in between. Seals  58  and  60  mounted to lower mandrel  52  maintain the integrity of passage  16 . Lower launch sleeve  62  is pinned to lower mandrel  52  by pins  70 . Dogs  64  are initially trapped in recess  66  in lower mandrel  52  by sleeve  56 . Dogs  64  extend through openings  68  in lower mandrel  52 . A shear pin or pins  70  retain lower launch sleeve  62  to lower mandrel  52 . Circumferentially offset from pins  70  are passages  72  that lead from passage  16  to chamber  74 . Seals  76  and  78  seal off the lower end of chamber  74 . Passage  80  leads from chamber  74  to passage  16  around sleeve  56 . 
     Upper wiper plug  82  has a recess  84  into which are trapped dogs  86  that pivot at  88  and have a torsion spring  90  to bias them radially inwardly when sleeves  26  and  46  move up as shown in  FIG. 4   c . Upper wiper plug  82  has external fins  92  and an internal bore  94  that allows it to be mounted over lower launch sleeve  62 . A flapper  96  is designed to close the bore  94  after the upper wiper plug is launched. 
     Lower wiper plug  98  is similar to upper plug  82  in that it has a bore  100  that allows it to be mounted over lower launch sleeve  62  and a flapper  102  that closes bore  100  after launch of lower wiper plug  98 . External fins  104  aid in propelling the plug  98  downhole. Lock dogs  106  have a bore  108  and a pin  110  extending though it to retain them to upper wiper plug  82 . In the  FIG. 1   c  position, the dogs  106  are trapped into recess  112  so as to support the lower wiper plug  98  off of the upper wiper plug  82 . Lower launch sleeve  62  has a recessed surface  114  that in  FIGS. 1   c  and  2   c  is offset from dogs  106 . A port  116  that will ultimately be used to flow cement is initially held closed by seals  118  and  120  on upper wiper plug  82 . Seal  122  on lower wiper plug  98  seals against launch sleeve  62  to allow pressure in annulus  18  to be used to propel the plug  98  after dogs  106  are undermined. Finally, sleeve  124  shown in  FIG. 1   c  supports upper wiper plug  82  against dogs  86  that are in turn held in recess  84  by lower segment  46 . If the running tool fails to function and release the liner wiper plugs, rupture disk  14  may be burst with applied internal pressure to serve as an emergency bypass for flow around the tool. 
     The major components now having been described, the operation of the tool will now be reviewed in detail. As shown in  FIG. 2   d  a first pump down plug  126  having a known design lands on shoulder  128  on lower launch sleeve  62  thus blocking the passage  16 . Port  116  is isolated by seals  118  and  120  at this time. As pressure is built up the first thing to happen is to break the shear pins  70  shown in two pieces in  FIGS. 3   b - 3   c . Launch sleeve  62  is able to move down after shear pins  70  are broken until shouldering on ring  124 . The downward movement of lower launch sleeve  62  allows dogs  64  in windows  68  to slide in elongated recess  66  which cams dogs  64  onto surface  130  so that they the move radially inwardly, having already cleared the lower end of sleeve  56  and now supports the dogs  64  in a position where they extend into passage  16  as seen by comparing  FIGS. 2   b  and  3   b . At the same time, as shown in  FIGS. 3   c - 3   d , the shifting of the lower launch sleeve  62  has placed recess  114  opposite dogs  106  to let them come out of lower wiper plug  98  so that it is launched and the port  116  is exposed for pumping cement behind the launched lower wiper plug  98 . As the lower wiper plug  98  leaves the lower launch sleeve  62  the flapper  102  is able to close so that the cement can then drive the plug  98  until it bumps surface  134  in the landing collar that is part of the casing or liner  20 . After bursting the rupture disk in flapper  102 , the cement continues through the landed plug and into the annulus around the casing or liner  20  in a known manner. 
     While the wiper plug  98  is being launched, the sleeve  26  is in pressure balance and can&#39;t move. This is because pressure in passage  16  of the tool communicates to port  22  to act on surface  136  to put an uphole force on upper sleeve  26 , see  FIG. 3   b . At the same time pressure in passage  16  communicates through ports  72  and  80  to surface  138  in cavity  74  that is sealed at seals  76  and  78 . The surface  138  has the same cross-sectional area as surface  136  so that there can be no net force applied to move sleeve  26 , which is initially pinned to the upper mandrel  10  with pin or pins  140 . It is worth repeating that dogs  64  remain retracted until pump down plug  126  passes and pressure buildup causes the lower launch sleeve  62  to shift camming the dogs  64  into passage  16  when only then can they be used to catch the next pump down plug  148  as shown in  FIG. 4   b.    
     Note that as lower launch sleeve  62  moves down it displaces fluid from cavity  142  through passages  144  and  146  as the volume of cavity  142  decreases until the lower launch sleeve&#39;s movement is stopped by hitting sleeve  124  as shown in  FIG. 3   c . At this point the cement port  116  is exposed to pass cement. 
     When the second pump down plug  148  lands on dogs  64  the ports  72  and  80  are isolated and pressure applied to passage  16  is now exclusively directed to ports  22 . An unopposed uphole force is now applied to surface  136  to shear pins  140 . As upper sleeve  26  moves up, its lower end  46  no longer covers dogs  86  putting the upper wiper plug in position for release as shown in  FIG. 4   c . The upward movement of sleeves  26  and  46  is locked in as snap ring  42  contracts against surface  44  as shown in  FIG. 5   a . Applied pressure above the wiper plug fins propels the released wiper plug  82  down the casing or liner  20  until it bumps lower wiper plug  98  as shown in  FIG. 7   a . The entire tool with retained pump down plugs  126  and  148  can be removed as an assembly from the well. 
     Those skilled in the art will now appreciate that the apparatus described above prevents the inadvertent release of two wiper plugs because not only is the upper plug release mechanism in pressure balance when the lower plug is released but the dogs  64  that allow the use of pump down plug  148  to ultimately overcome that pressure balanced configuration are held retracted making them inaccessible to the initial pump down plug  126  as it travels past to its position shown in  FIG. 2   d . There is no way to accidentally release the upper wiper plug  82  before the lower plug  98  is released. In prior designs, such as FIG. 9 of U.S. Pat. No. 5,553,667 the release mechanism for the upper plug is exposed and the lower pump down plug has to travel through it where it can get lodged and result in launching both plugs. Even though the first pump down plug in that prior design is made smaller to fit through the release mechanism of the upper plug the possibility exists that the wrong shear device will fail first and release both wiper plugs. In the present invention, not only is the release mechanism in pressure balance from pressure buildup in passage  16  with pump down plug  126  landed but the movement of the first pump down plug to its landing shoulder  128  while there is no higher shoulder for that pump down plug  126  to land on that would in any way allow an unbalanced pressure force to be applied to the upper release sleeve  26 . 
     The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.