Patent Application
20090188664
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.
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'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.
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.
a-1d show a half section of the tool in the run in position;
a-2d show the tool of
a-3d show the tool of
a-4d show the tool of
a-5d show the tool of
a-7b show both launched wiper plugs captured in a landing collar downhole.
Referring to
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
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
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
The major components now having been described, the operation of the tool will now be reviewed in detail. As shown in
While the wiper plug 98 is being launched, the sleeve 26 is in pressure balance and can'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
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's movement is stopped by hitting sleeve 124 as shown in
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
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
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.
