Cementing plug

Details Cementing plug Cementing plug

1999-06-04

2001-05-29

Bagnell, David (Department: 3672)

Wells

Pistons, fluid driven into well

C166S291000

Reexamination Certificate

active

06237686

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a cementing plug and, more particularly to an easily drillable plug for use in well cementing operations.
BACKGROUND OF THE INVENTION
It is conventional practice, in the drilling and completion of wells, that prior to the placement of cement, the casing and hole are filled with drilling mud. In order to reduce contamination of the interface between the mud and the cement a bottom cementing plug is placed in the casing and pumped ahead of the cement slurry. The bottom plug is typically constructed with a one piece hollow metallic or a one piece non-metallic core having an elastomer covering molded to the core. The elastomer cover typically incorporates a plurality of wipers. The function of the wipers is to wipe the internal surface of the casing, maintain the separation of fluids during the displacement of the cement slurry down the casing and provide a means of sealing upon displacement of the plug. The bottom plug incorporates a rupture diaphragm that will rupture upon the bottom plug reaching a float shoe, float collar or landing collar located near or at the bottom of the casing. When the bottom plug reaches the float shoe, float collar or landing collar, the increase in fluid pressure will result in the diaphragm rupturing allowing the cement slurry to pass though the bottom plug and continue out the bottom of the casing, filling the space between the casing and the well bore.
Upon placing all the cement into the casing a top plug is located on top of the cement. The top plug is typically constructed having a solid elastomer, one piece metallic or one piece non-metallic core having an elastomer covering molded to the core, the elastomer cover incorporating a plurality of wipers. The function of the wipers is to wipe the internal surface of the casing, maintain the separation of fluid during the displacement of cement slurry down the casing and provide a method of providing a sealing mechanism upon landing the top plug on top of the bottom plug. When displacement of the cement slurry is complete the top plug will land on top of the bottom plug remaining in this position. The required length for the top plug and the bottom plug varies with the intended application, and is based upon a number of factors including the pressure being contained.
After the cement slurry has become hard, the top and bottom plugs are drilled out using a drilling bit. Typical prior art cementing plug sets incorporate teeth, lugs or threads that act to prevent the plugs from rotating during the drill-out procedure, thereby reducing the time required to perform the drill-out operation.
SUMMARY OF THE INVENTION
What is required is an alternative configuration of cementing plug.
According to the present invention there is provided a cementing plug which includes a plurality of body segments. Means is provided for securing the plurality of body segments together to form a plug body. Elastomer wipers clamped between the body segments.
The use of a plurality of body segments enables plugs to be produced of varying lengths without having to produce additional molds for molding the plastic cores and elastomer covers. Prior art cement plugs used a one-piece molded core ith a one piece molded elastomer covering. To manufacture the prior art cementing plugs, molds for the plastic cores and molds for the elastomer covers were produced with each mold producing a plug of a set length. With the prior art should it be desired to produce a plug of shorter or longer length of a plug with an increased or decreased number of wipers a new set of molds would be produced to manufacture the new plug. The present invention allows the plug length and the number of wipers incorporated in the plug to be varied by the adding additional segmented plastic cores and wipers. It is intended that each of the body segments be substantially identical, but this is not essential. There are a variety of ways of securing the body segments together, several of which will hereinafter be further described.
Although beneficial results may be obtained through the use of the cementing plug, as described above, even more beneficial results may be obtained when the body segments are made from polymer plastic. Metal and rubber are difficult to drill. With the cementing plug, as described above, the metal and rubber can largely be replaced with more drillable materials, such as plastics.
Although beneficial results may be obtained through the use of the cementing plug, as described above, even more beneficial results may be obtained when a variety of elastomer wipers are used made from elastomers with differing properties. The prior art cementing plugs covered a core with an elastomer cover. This necessarily required that the elastomer wipers be made of the same elastomer materials as the elastomer cover. The selection of elastomer materials, therefore, was of importance. Some elastomers work more effectively for wiping, other elastomers work better at elevated temperatures, other elastomers have better wear properties and other elastomers have better compatibility with specific wellbore fluids. With the cementing plug, as described above, the elastomer wipers need not all have the same properties. A number of elastomer wipers with differing properties can, therefore, be configured to improve performance of the plug in a wide range of downhole operating conditions and fluids. In addition, the cementing plug described above has reduced the amount of elastomer material used, by using individual wipers that are locked between the molded plastic segments which replaces much of the elastomer material with plastic. The elastomer cover that normally covers the core between the wipers is eliminated, which improves the ability to drill out the plugs.
Although beneficial results may be obtained through the use of the cementing plug, as described above, it is important that the elastomer wipers be securely attached to the plug body. Even more beneficial results have, therefore, be obtained when the body segments have opposed mating faces with a receptacle on each of the faces, and each of the elastomer wipers has radial projections. The radial projections are received in the receptacles of mating body segments to lock the elastomer wipers to the plug body.
Although beneficial results may be obtained through the use of the cementing plug, as described above, it slow the drilling process if the body segments rotate when a force is exerted upon them by a drill bit during drilling out of the cementing plug. Even more beneficial results may, therefore, be obtained when the body segments have a projecting lug on one face and a lug receiving aperture on an opposed face. When the body segments are secured together, the projecting lug of one of the body segments engages the lug receiving aperture of another of the body segments to prevent relative rotation of the body segments.


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patent: WO93/08366 (1992-10-01), None
patent: WO94/11610 (1993-11-01), None

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