The present invention relates to a plug device. More particularly, it concerns a plug device for use when temporarily sealing a fluid bore in a pipe, wherein the plug device includes a plug body disposed in a sealing manner in the fluid bore.

When preparing e.g. wells for the recovery of oil and gas from the earth's crust, a so-called completion string is set. The completion string includes a temporary well barrier structured in a manner allowing it to withstand the pressure from the well until a hydraulically operated production packer has been set and function tested.

Upon having found the production packer to be in good order, the temporary well barrier is removed.

Upon having removed the temporary well barrier, it is desirable for the production tubing string to be free of constrictions .

A so-called glass packer is known, the packer of which is blown to pieces by means of an explosive when the glass packer is to be removed, the detonation being controlled from the surface of the well. The fragments or pieces are then produced out of the well.

Experience goes to show that problems sometimes arise with respect to detonating the explosive. In such incidents, the glass packer may be crushed by means of, for example, a body introduced into the well from surface. The crushed packer is then produced out of the well.

Even though such a crushing operation normally will not affect the production of the well, the well will contain an undetonated explosive not possible to control . Such explosives are relatively powerful and may represent a considerable safety risk for the installation associated with the well.

The use of explosives also represents a safety risk with respect to preparation of the plug device, typically onshore, and in connection with transport to the well.

The object of the invention is to remedy or to reduce at least one of the disadvantages of the prior art.

The object is achieved by virtue of features disclosed in the following description and in the subsequent claims.

In this document, positional references, such as "upper", "lower", "upstream" and "downstream", refer to positions shown in the figures, the positions of which will be natural in the situation of use.

In a first aspect of the present invention, a plug device for use when temporarily sealing a fluid bore in a pipe is provided, wherein the plug device includes a plug body disposed in a sealing manner in the fluid bore, and wherein the plug device further comprises a piston arrangement structured in a manner allowing it to provide a pressure increase in an activation fluid having been introduced to the plug body via at least one channel .

The pipe may, for example, be a well pipe used in connection with the recovery of petroleum.

The piston arrangement may be disposed between a drive fluid and the plug body, the drive fluid being arranged to drive the piston arrangement from a first position onto a second position.

In a preferred embodiment, the activation fluid is at a first pressure when the piston arrangement is located in the first position, and at a second, higher pressure when the piston arrangement is located in the second position, and wherein the plug body is structured to disintegrate at a disintegration pressure being equal to or lower than the second pressure. In this document, the term disintegrate is taken to mean that the plug body becomes sufficiently deformed to allow it to be produced out through the well pipe, for example by virtue of the plug body being crushed or split into two or more smaller pieces.

The piston arrangement may include a first piston which, by means of a piston rod, is connected to a second piston. It is to be appreciated, however, that the piston arrangement may be comprised of more than two pistons connected in series with one another by means of a piston rod connecting one piston to a consecutive piston.

The first piston may be provided with an outer piston surface exposed to the drive fluid, and an inner piston surface exposed to a first fluid located in a first fluid chamber, and wherein the second piston is exposed to the activation fluid located in a second fluid chamber. In one embodiment, the first fluid chamber is an annular space defined by a portion of the piston arrangement and a jacket portion of the plug device.

Advantageously, the first fluid is more compressible than the activation fluid. The effect thereof is that the fluid in the first fluid chamber offers little resistance, relatively speaking, upon movement of the first piston, whereby as much as possible of the power of the drive fluid is transmitted to the activation fluid located in the second fluid chamber. For such an embodiment, the first fluid chamber will provide a travel path for the first piston.

Preferably, the first fluid is a gas, and the activating fluid preferably is a liquid.

The first fluid chamber may, for example, contain air at atmospheric pressure.

The second fluid chamber may, for example, contain oil.

Typically, the fluid pressure in the second fluid chamber initially is in the order of 1-500 bars, preferably 1-250 bars. In some instances, a higher fluid pressure in the second fluid chamber may also be required.

Preferably, the area of the piston surface of the first piston, the area of which is exposed to the drive fluid, is larger than the area of the bottom piston surface of the first piston, the area of which is exposed to the first fluid chamber. The effect thereof is that the pressure transmitted to the fluid in the first fluid chamber becomes larger, relatively speaking, than the pressure of the drive fluid because the pressure is inversely proportional to the area of the piston surface. Advantageously, and for the same reason, the area of the piston surface of the first piston, the area of which is exposed to the drive fluid, is larger than the area of the portion of the second piston, the area of which is exposed to the second fluid chamber containing the activation fluid.

It is to be appreciated that, in the case of the piston arrangement comprising more than two pistons, each piston will be exposed to a corresponding fluid chamber, as explained above. To be able to achieve a pressure increase from one piston to another, following piston, the piston area of one piston must be larger than the piston area of the piston following, as explained above.

In a preferred embodiment, the plug body is comprised of a hollow body made of a frangible material. A frangible material is more readily disintegrated into two or more pieces than a resilient material .

In one embodiment, the hollow body is filled with the activation fluid. When the pressure of the activation fluid is increased, the internal pressure of the plug body will increase until the plug body is disintegrated.

Advantageously, at least portions of the fluid-filled plug body are provided with an outer surface being convex in the longitudinal direction of the well pipe. Having such a design, the plug body will be able to better withstand external forces than internal forces .

The above-mentioned combination of a gas-filled first fluid chamber, a liquid- filled second fluid chamber and the differences between the areas of the pistons, provides a very good effect with respect to disintegrating the plug body.

In an alternative embodiment, the activation fluid may exert such a large external pressure on the plug body that it disintegrates, either by virtue of the very fluid, or by virtue of a body being pushed against the plug body by means of the activation fluid so as to be disintegrated. Tests have shown that the best disintegration effect is achieved by allowing said body to be pushed at great speed or to be rammed against the plug body.

Preferably, the frangible material is one of, or a combination of, a ceramic material or a glass material, both of which are capable of being crushed into two or more pieces, or a composite material of a type capable of being crushed into two or more pieces. For example, and not limited thereto, the composite material may be comprised of a material made from carbon, plastics or bakelite.

The plug device may be provided with a rupture element structured to fix the piston arrangement against movement until the drive fluid exceeds a predetermined pressure at which the rupture element ruptures. For example, and not limited thereto, the rupture element may be a shear ring or a sleeve provided with a pre-weakened portion constituting a so-called failure locator, or the rupture element may be comprised of so-called shear pins capable of fixing the piston arrangement against movement. An example of a failure locator in a shear ring is indicated by broken lines in figure 1. The purpose of a rupture element is to render possible to increase the pressure on the piston arrangement whilst being retained, and simultaneous with the pressure being increasing until the rupture element ruptures and the piston arrangement is put into rapid, downward movement. Such a rapid movement will bring about a considerable activation fluid pressure surge against the plug body.

In a second aspect, a method of removing a plug body placed in a plug device and disposed in a sealing manner in a fluid bore in a pipe is provided, wherein the method includes the steps of :

- pressurizing a drive fluid located at a downstream side of a fluid flow against which the plug body seals;

- providing movement of a piston arrangement, which is included in the plug device, from a first position onto a second position in order to produce an increase in the fluid pressure of an activation fluid being in fluid communication with a portion of the plug body; and

- allowing the pressure of the drive fluid to increase until the plug body disintegrates, and then terminating the pressurization at the downstream side of the plug device.

The method may further include producing the disintegrated plug body out of the well.

In a third aspect, the invention relates to the use of a fluid at high pressure in order to disintegrate a plug body in a fluid bore.

Hereinafter, an example of a preferred embodiment is described and is depicted in the accompanying drawings, where :

Figure 1 shows a front elevation, in section, of a plug device according to the present invention before a supplied drive pressure has severed a rupture element in the form of a shear ring fixing a piston arrangement to the plug device; and

Figure 2 shows the plug device of figure 1 after the drive pressure has severed the shear ring, whereby the piston arrangement has been moved downwards in the plug device and thus has produced an activation pressure having disintegrated a plug body in the plug device.

In the figures, reference numeral 1 denotes a plug device in accordance with the present invention, wherein the plug device 1 is defined, in the longitudinal direction thereof, by an upper adapter 3 and a lower adapter 5. Each of the adapters 3, 5 is connected to a well pipe 7 by means of threaded connections. Although not shown in the figures, a person skilled in the art will appreciate that also the lower portion of the lower adapter is connected to a well pipe.

The adapters 3 , 5 are connected to connectors known per se (three shown) denoted in general by reference numerals 9, 9', 9", whereby the plug device 1 includes a train of adapters 3, 5 and connectors 9, 9', 9" screwed together and skilfully adapted to allow them to be disposed at dedicated places in the plug device 1.

Together the adapters 3 , 5 and connectors 9 form the outer housing or enclosure of the plug device 1. In the embodiment shown, which is also a preferred embodiment, the plug device 1 has an external diameter corresponding to the external diameter of the well pipe 7 at the upstream and downstream sides of the plug device 1.

A production bore 11, which extends coaxially through the plug device 1 with respect to the centre axis of the plug device 1, is in fluid communication with the well pipe's production bore 11 ' located at the upstream and downstream sides (not shown) of the plug device 1.

Further, the plug device 1 comprises a piston arrangement 20, which includes a first annular piston 22 and a second annular piston 24. The first annular piston 22 is connected to the second annular piston 24 by means of a first piston rod 26 extending from the first annular piston 22 and being thread- connected to a lip portion 28 of the second annular piston 24. It is to be appreciated that the piston arrangement 20 may comprise more than the two annular pistons 22, 24 shown, 5 wherein the pistons are arranged in series according to the same principle explained in this document and shown in the figures.

Due to the connection between the annular pistons 22, 24, a movement of the first annular piston 22 will bring about ao corresponding movement of the second annular piston 24.

The movements of the first annular piston 22 and the second annular piston 24 are restricted by a first fluid chamber 30 and a second fluid chamber 32, respectively. Hereinafter, the first fluid chamber 30 will also be referred to as an annulars space 30.

' By means of a fluid line 34, the second fluid chamber 32 is in fluid communication with the interior of a plug body 36.

In figure 1, the piston arrangement 22, 24, 26 is fixed in an initial position by means of a rupture body, which is a shear0 ring 40 in the embodiment shown. The shear ring 40 is fixed to the first annular piston 22 for the locking thereof, hence the entire piston arrangement 22, 24, 26, to the upper adapter 3. In the initial position, the annular space 30 and the second fluid chamber 32 assume a maximum volume of fluid5 and a corresponding minimum fluid pressure.

It is to be appreciated that the fluid chambers 30, 32 are secured against leakage by means of gaskets known per se. The gaskets are shown in the figures but are not denoted specifically with reference numerals. o Upon exposing a fluid to a pressure increase in a manner known per se, the fluid of which is located in e.g. the well pipe 7 above the plug body 36 of the plug device 1, the increased pressure will be absorbed initially by the shear ring 40 fixing the piston arrangement 20 against movement. By so doing, the pressurized fluid will discharge through openings 42 in the jacket of the shear ring 40 so as to exert a compressive force on a piston surface 22 ' of the first annular piston 22.

Hereinafter, said fluid will also be referred to as a drive fluid.

As the fluid pressure gradually increases, finally it will exert a compressive force against the piston surface 22 ', hence against the shear ring 40, exceeding the shear strength of the shear ring 40. When this happens, the shear ring 40 will be divided in two, and the piston arrangement 20 will be put into downward movement .

The first fluid chamber or annular space 30 contains a compressible fluid. Advantageously, tests have shown that the annular space 30 may contain air at atmospheric pressure. Alternatively, it is to be appreciated, however, that the first fluid chamber 30 may be filled with other gases having another pressure than atmospheric pressure, also pressures being lower than atmospheric pressure, whereby the annular space 30 is at underpressure. One of the advantages of using air at atmospheric pressure is that it simplifies the manufacturing process of the plug device while, at the same time, it becomes safer.

The air in the annular space 30 offers little resistance, relatively speaking, to the force transmitted via an inner piston surface 30 ' upon movement of the first annular piston 22, insofar as the air is easily compressible, relatively speaking, by the drive fluid acting on the piston surface 22 '.

In one embodiment (not shown) , the upper adapter 3 is provided with one or more bores extending between the first 5 fluid chamber 30 onwards to the outside of the adapter 3. The purpose of the bore(s) is to allow the fluid in the first fluid chamber 30 to be evacuated upon being compressed in response to the downward movement of the first annular piston 22. o The movement of the first annular piston 22 will be transmitted via the piston rod 26 onto the second annular piston 24, and the downward movement of the annular pistons 22, 24 will continue as long as the resultant force from the drive fluid, together with the kinetic energy of the pistons arrangement 20 and the severed shear ring 40, exceeds the counter-forces exerted by the fluids located in the first fluid chamber 30 and the second fluid chamber 32.

As the second annular piston 24 is being moved downwards (in the direction towards the plug body 36) , an incompressible0 fluid, for example oil, in the second fluid chamber 32 will be forced out therefrom and will flow via the fluid line 34 and into the plug body 36. As the incompressible fluid gradually flows into the plug body 36, the fluid pressure therein will increase. At a predetermined pressure, the plug5 body 36 will be disintegrated and open to fluid throughput in the production bore 11, 11'.

Upon having disintegrated the plug body 36, as shown in figure 2, the fluid in the second fluid chamber 32 has been drained into the production fluid flowing within the o production bore 11, 11'.

Until establishing fluid flow in the production bore 11, H', the drive fluid, which caused the shear ring 40 to be divided, will fill a volume 33 above the piston arrangement 20.

Due to the piston arrangement 20 having experienced a 5 downward movement, an annular space 33 ' will form above the second piston 24.

Advantageously, and in order to allow the disintegrated plug body 36 to be produced out of the well, the plug body 36 disintegrates into several fragments. It is therefore o advantageous for the plug body 36 to be made from a frangible material, for example such as, but not limited to, a ceramic material known per se or a glass material.

To be able to withstand the pressure from the well fluid in the well pipe 7 at the upstream side of the plug body 36, thes plug body 36 exhibits a convex surface towards said well fluid. Correspondingly, a concave shape towards the internal fluid of the plug body 36 will facilitate the disintegration of the plug body 36 as the internal fluid exerts a pressure against the internal jacket surface of the plug body 36. 0 From the description above, a person skilled in the art will appreciate that the shear ring 40 must be structured to be severed by a force being smaller than the force for which the plug body 36 is structured to withstand, whereby the shear ring 40 is severed before the plug body 36 ruptures. 5 Thus, the plug body 36 in the plug device 1 according to the invention may be disintegrated in a controlled and safe manner without the use of explosives or objects introduced into the well.

It is to be appreciated, however, that the plug body o according to the present invention also may be disintegrated by virtue of means known per se, which are released or introduced into the fluid bore 11. Such known means may, for example, be ^" a ball, a rod or a so-called "prong".

The disintegrated plug body may then be produced out of the well .