A device for a running tool for a wellbore plug is described, arranged to sealingly abut, by radial expansion, against a wellbore wall, a hydraulic actuator being arranged to be connected to the wellbore plug, and a first portion of a housing forming a piston chamber accommodating a working piston arranged to be connected to the wellbore plug by means of a piston rod.

In the course of well operations during oil and gas

exploration and production, plugs are often used to separate a wellbore portion from the rest of the wellbore. Such plugs may be set, that is to say activated by expansion thereof into abutment against the wellbore wall, by the use of a hydraulic system, as one or more actuators associated with the plug displace (s) one or more plug elements in an axial direction in order thereby to expand the plug in the radial direction into sealing abutment against the wellbore wall.

Running tools of the hydraulic type often have the drawback of having a relative large building length.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through the features which are specified in the description below and in the claims that follow .

A running tool for a wellbore plug is provided, in which the wellbore plug abuts against an end portion of a housing and is connected to a piston rod in such a way that when the piston rod is moved in the axial direction of the housing away from the wellbore plug, the plug expands in the radial direction. The wellbore plug in itself is not described any further as the running tool according to the invention can be used for a wide range of plug types.

The housing forms a piston chamber defined between a fixed end-wall element and a floating end piston. The end-wall element is provided with a through opening for the piston rod, and an internal end-wall opening wall is provided with fluid-sealing piston rod gaskets abutting against the piston rod. The piston rod is attached to a working piston which is axially displaceable in the piston chamber. A hydraulic pump and an associated electric motor are fixed to the working piston. Wires arranged for the. power supply to the motor are extended through the end piston in a fluid-sealing manner and exhibit sufficient slack for the end piston and the working piston to be displaceable relative to each other without the wires restraining such movement.

The floating end piston makes the volume of the piston chamber change in accordance with the displacement of the working piston, this displacement resulting in a varying portion of the piston rod occupying a partial volume of the piston chamber. Thus, there is no need for a hydraulic-fluid accumulator outside the piston chamber.

The working piston and the pump are put together in such a way that one or more fluid lines is/are provided between a first fluid port in the pump and a first portion of the piston chamber defined by the working piston and the end-wall element, in order that a prescribed working pressure may thereby be applied to this piston chamber portion.

A second fluid port in the pump is in fluid communication with a second portion of the piston chamber which is defined by the working piston and the floating piston.

When the running tool is ready for operation, the piston chamber is filled with an appropriate hydraulic fluid.

The end-wall element may be provided with a closable drain line to be used when, among other things, the piston chamber is being filled with the hydraulic fluid, evacuation of any undesired content of gas being enabled through the drain opening.

At least the portion of the housing forming the piston chamber is formed of a cylinder-shaped body. The housing may be formed of two tubular bodies which are joined together by means of the end-wall element, preferably by the opposite pipe end portions being provided with threads which are arranged to engage corresponding threaded portions on the end-wall element. The housing preferably exhibits an

external, uniform mantle surface.

The motor may be a brushless electric motor.

The invention relates more specifically to a device for a running tool for a wellbore plug arranged to sealingly abut, by radial expansion, against a wellbore wall, a hydraulic actuator being arranged to be connected to the wellbore plug, and a first portion of a housing forming a piston chamber which accommodates a working piston arranged to be connected to the wellbore plug by means of a piston rod, characterized by

the piston chamber being defined by an end-wall element which is fixed to the housing, and an end piston which is arranged in an axially floating manner in said portion of the housing; and

a hydraulic pump and an associated driving motor being fixed to the working piston.

First and second portions of the piston chamber may be interconnected in a fluid-communicating manner by way of the hydraulic pump.

A pressure-fluid line may form a fluid communication between a piston-rod chamber and the hydraulic pump.

The housing may be provided with a well-fluid passage which forms a fluid communication between an end piston chamber, which is defined by the end section and the end piston, and the surroundings .

A closable drain line may be arranged in the end-wall

element, extending between the piston chamber and an external surface of the end-wall element.

A second pipe body may form a supporting abutment between the end-wall element and the wellbore plug.

The end piston may be provided with one or more fluid-sealing wire passages arranged substantially in the axial direction of the end piston.

In what follows, an example of a preferred embodiment is described, which is visualized in the accompanying drawing, in which:

Figure 1 shows a side view of a running tool and an

associated wellbore plug (shown schematically) , in which, for reasons of exposition, a housing has been cut through.

A running tool according to the invention includes a housing

I formed of first and second pipe bodies 11, 12. The second pipe body 12 is attached to an end-wall portion 111 of the first pipe body 11 by means of a threaded connection 116, 121. Opposite the end-wall portion 111, the first pipe body

II is provided with an end section 14 which is arranged to be connected to equipment, not shown, for moving the housing 1 forward in a wellbore 8. The housing 1 is arranged to be connected to a wellbore plug 7 of a kind known per se which may, by compression, abut against a wellbore wall 81 defining the wellbore 8 towards a structure 9. In the figure, only part of the wellbore 8 and the surrounding structure 9 is shown. An end portion 122 of the second pipe body 12 is arranged to form an abutment for the wellbore plug 7 when this is to be compressed. Compression elements (not shown) in the wellbore plug 7 are connected to the piston rod 22 of a working piston 2.

The working piston 2 is arranged in a piston chamber 3 formed in the housing 1 between the end-wall portion 111 and a floating end piston 6, the working piston 2 forming an interface between first and second piston chamber portions 31, 32. The first piston chamber portion 31 is also called a piston-rod chamber. In a manner known per se, the working piston 2 is provided with piston gaskets 21 sealingly

abutting against an internal wall 117 of the first pipe body 11. In a fluid-sealing manner, the piston rod 22 projecting from the piston 2 is passed through a piston-rod opening 112 in the end-wall portion 111, where piston-rod gaskets 113 sit sealingly between the wall surface of the piston-rod opening 112 and the periphery of the piston rod 22. Opposite the piston rod 22, a hydraulic pump 4 provided with a suction port 43, which is in fluid communication with the second piston chamber portion 32, is attached to the piston 2. A pressure port (not shown) in the hydraulic pump 4 is in fluid communication with the piston-rod chamber 31 via a pressure- fluid line 23 opening at the periphery of the piston rod 22 near the piston 2. Even though the ports of the hydraulic pump 4 are termed "suction port" and "pressure port" here, it will be obvious to a person skilled in the art that a hydraulic pump of this kind can be reversed, so that the delivery of fluid is reversed in relation to that described in what follows.

A driving motor 5, preferably a brushless electric motor, is connected to the hydraulic pump 4 via a motor coupling 51. Motor wires 52 which are arranged for power supply from a remote energy source (not shown) , are extended in a fluid- sealing manner through a wire passage 62 in the end piston 6 and further on through the end section 14 and away from the housing 1. The motor wires 52 exhibit sufficient slack between the driving motor 5 and the end piston 6 for the pistons 2, 6 to be moved to a maximum distance without the motor wires 52 being subjected to strain.

Near the end section 14, the housing 1 is provided with a well-fluid passage 13. When the running tool is operative, an end piston chamber 63 defined by the end section 14 and the end piston 6 will be filled with well fluid 82 present in the wellbore 8.

The end piston 6 is provided with end-piston gaskets 61 abutting in a fluid- sealing manner against the internal wall 117 of the first pipe body 11.

In the end-wall portion 111, a closable drain line 114 is formed, fluid-communicatingly connecting the piston chamber 3 to the surroundings. The drain line 114 can be closed by means of a closing plug 115. The drain line 114 is used when the piston chamber 3 is to be filled with and emptied of hydraulic fluid 33.

When the running tool according to the invention is lowered into the wellbore 2, the internal pressure of the running tool is balanced with the pressure in the wellbore 8, the well fluid 82 filling the end volumes of the housing 1, that is to say the volume between the floating end piston 6 and the end section 14 through the well-fluid passage 13, and the volume of the second pipe body 12 as the end portion 122 is open to the surroundings. The well pressure will propagate to the piston chamber 3 by the end piston 6 floating.

When the associated wellbore plug 7 is to be set,

overpressure is generated in the piston-rod chamber 31 by the hydraulic pump 4 being activated by means of the driving motor 5. Hydraulic fluid 33 is pumped through the piston 2 via the pressure-fluid line 23 from the second piston-chamber portion 32 into the piston-rod chamber 31, and the piston 2 is pushed away from the end-wall portion 111. The piston rod 22 pulls the well-bore plug 7 into abutment against the end portion 122 of the second pipe body 12 so that the wellbore plug 7 expands, in a manner known per se, into sealing abutment against the wellbore wall 81.

The difference in displacement volumes of the two partial chambers 31, 32 owing to the varying occupation of volume by the piston rod 22 in the first piston-chamber portion 31 is compensated by the floating end piston 6 being displaced so that the pressure within the second piston-chamber portion 32 remains in balance with the pressure of the well fluid 82. Preferably, the driving motor 5 is a brushless electric motor. The driving motor 5 being in the piston chamber 3 which is filled with hydraulic fluid 33, the driving motor i shielded from contact with the well fluid 82 which may be electrically conductive. The driving motor 5 may thereby be submerged in the electrically non-conductive hydraulic fluid 33, which is, for example, a suitable hydraulic oil, and there is no need to shield the driving motor 5 any further, for example by fluid-tight encasing. The running tool according to the invention thereby provides an arrangement which exhibits a great degree of reliability, the running tool being little vulnerable to pressure influence from the well fluid 82.