Wells – Processes – Placing or shifting well part
Reexamination Certificate
1999-07-20
2001-06-12
Bagnell, David (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S332100
Reexamination Certificate
active
06244350
ABSTRACT:
This invention relates to an apparatus for launching at least one plug into a tubular in a wellbore, for example, a liner in an oil or gas well. Wiper plugs are generally, but not exclusively used in connection with the cementing of such liners.
In the cementing of casing and liners in a wellbore, the annular space between the casing/lining and the wellbore is filled with a predetermined quantity of a cement mixture which, after hardening, retains the casing/liner in place in the wellbore.
The cement mixture is pumped in at the top end of the casing or liner, down to the lower end thereof and out into and up the annular space on the outside of the casing/liner.
Before the cement mixture is pumped into the casing/liner, it is usual, although not essential, for a first plug to be introduced at the top of the casing/liner which slides in a sealing-tight relationship against the casing/liner. When a predetermined quantity of cement mixture has been introduced into the casing/liner, a second plug is introduced in order to separate the cement mixture from a well liquid which is thereafter supplied under pressure to drive the cement mixture into the casing/liner. The first plug is adapted to be opened for cement mixture to flow therethrough when the plug lands at the lower end of the casing/liner. The cement mixture thereafter flows through the first plug, comes into contact with and displaces liquid which is in the annular space, and pressure from the liquid supplied from the surface acts behind the second plug and pushes thereon until it lands on the first plug.
Sometimes it is disadvantageous to have direct contact between the cement mixture and the liquid in the well and the annular space, since undesirable chemical reactions may take place. In that case a suitable liquid is pumped ahead of the cement mixture. This is done by introducing into the casing/liner a first plug, a separating liquid, a second plug, cement mixture, and finally a third plug. Therefore, the cement mixture substantially only comes into contact only with the separating liquid. It may also be advantageous to pump a number of special liquids through the liner/casing, both before and after the cement mixture, thereby necessitating a number of further plugs.
Generally, in the cementing of liners use is made of plugs having a central opening, so that the liquid can flow therethrough which are placed at the top of the liner. When the plug is to be launched, a sealing element such as a dart is introduced into the stream of liquid from the surface. The sealing element arrives on the plug and seals said central opening, and the water pressure then drives the sealed plug down the liner.
The above described design has been known to fail in use by either launching at least two plugs simultaneously, or by failing to launch any plugs.
According to the present invention, there is provided an apparatus for launching at least one plug into a tubular in a wellbore, said apparatus comprising a hollow upper section and a hollow lower section said hollow upper section comprising at least first and second upper ports longitudinally spaced therein, said second upper port being disposed above said first upper port, a landing seat between said hollow upper section and said hollow lower section, and a fluid displaceable member retained below said second upper port, said hollow lower section adapted to retain at least one plug and comprising at least a first lower port thereabove and a landing collar for said fluid displaceable member, the arrangement being such that in use, when the apparatus is installed at the top of a liner and lowered into a wellbore, and a dart lands on said landing seat blocking said first upper port allowing a fluid pressure differential to be created about said fluid displaceable member through said second upper port which displaces said fluid displaceable member to said landing collar, allowing a fluid pressure differential about said plug through said first lower port to launch said plug.
Preferably, said apparatus further comprises a third upper port in said hollow upper section above said second upper port and a second fluid displaceable member retained below said third port said hollow lower section adapted to retain a second plug, and comprising a second lower port thereabove, so that in use, a second dart lands on said first dart blocking said second upper port it allows a fluid pressure differential to be created about said second fluid displaceable member through said second upper port which displaces said second fluid displaceable member to said first fluid displaceable member blocking said first lower port, allowing a fluid pressure differential about said second plug through said second lower port to launch said second plug.
Advantageously, said fluid displaceable member is a sleeve which, in use, substantially blocks the annulus between the apparatus and the tubular.
When the sleeves come into the lower position, they produce the required effect by closing the liquid supply to the underside of the plug which is to be discharged from the apparatus into the liner. The pressure on the top side of the plug then displaces the plug downwards in the apparatus. The first sleeve closes the outlet of the annular space at the bottom, the second sleeve closing ports which conduct liquid from the annular space to the underside of the second plug. A third sleeve will close ports which conduct liquid from the annular space to the underside of a third plug, and so on.
Preferably, said fluid displaceable member is shear pinned to said apparatus.
Advantageously, said landing seat blocks a central fluid path between said hollow upper sections and said hollow lower sections.
Preferably, each port is the form of a horizontal row of ports.
Advantageously, said hollow upper section and said hollow lower section are of circular cross-section having equal outer diameters.
Preferably, the fluid displaceable member comprises a seal.
There is also provided a method for launching at least one plug using the apparatus defined hereabove.
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Gudmestad Tarald
Salte Jone
Bagnell David
Hawkins Jennifer M
McClung Guy
Weatherford / Lamb, Inc.
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