GB2160241A - Lifting device - Google Patents

Abstract

A lifting device for use on a downhole wireline and having first and second pistons 5, 8 of differing effective cross-sectional area, the smaller piston 5 being actuated by application of a lifting force and the larger piston 8 being secured to an item to be lifted, the cylinders 6, 2 pistons being in fluid communication eg via ports 7 so that movement of one induces movement in the other. Releasable means are provided for holding the device against axial movement relative to the borehole in which it operates. <IMAGE>

Description

SPECIFICATION Lifting device This invention relates to a lifting device.

In oil production a wire is run from the surface of the well and is used to guide pieces of equipment which require to be lowered into the well tubing. The wireline is also used to retrieve such equipment when it is no longer needed.

The wireline is maintained under tension, and when equipment is being retrieved it is attached to the wireline which is then withdrawn to the surface, taking the equipment with it. However, in some instances the equipment may be difficult to free from the well tubing, and considerable force may have to be applied to the wireline, causing occasional breakage of the wire. In this event another wireline has to be run and attached to the equipment, and the operation retried.

In general the wireline is a single strand of steel wire with a tension of around 550 kg.

An object of this invention is to provide apparatus which allows an applied lifting force on a wireline to be effectively increased at the equipment being lifted.

According to the present invention there is provided a lifting device comprising a first piston having means for connection to lifting means and movable in a first cylinder, a second piston having means for connection to equipment to be lifted and movable within a second cylinder, the first and second cylinders being in fluid communication and the second piston having a greater effective surface area than the first piston, and means for locking at least one of the first and second cylinders against movement, the arrangement of fluid communication between the first and second cylinders being such that movement of the first piston within the first cylinder produces movement of the second piston within the second cylinder.

The ratio of effective surface areas of the first and second pistons may be selected in accordance with practical considerations, but typical ratios are between 1:2 and 1:8.

Preferably the first cylinder extends within the second cylinder, for example by being coaxial with it, so that the apparatus can fit within a borehole; in this case the second piston may be secured to the first cylinder so that they are movable together, and the first cylinder may carry the means for attachment to the equipment to be lifted.

The locking means may be for example pistons which are movable radially of the first or second cylinders to engage an internal surface of a borehole tubing within which the apparatus may be disposed; these locking pistons may be actuable in response to movement of the first piston, whereby fluid displaced by the first piston pressurises one side of the second piston and also one side of the laterally-movable locking pistons. The arrange ment is preferably such that the laterally movable locking pistons are actuated before the second piston.

The locking means preferably includes provision for release when the tension in the wireline is reduced, so that the apparatus can then be freely moved along the borehole.

Such provision can be made by spring biassing the locking means out of engagement.

The apparatus of the invention is preferably fitted to the wireline through a series of interconnected jars, a stem and a rope socket, these items being as in conventional wirelines.

The second piston may be connected to a "fishing tool" for retrieving equipment from a subsea wellhead.

The first and second pistons may be springbiassed to return to their original positions on release of the tension in the wireline.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing, which is a part-sectional side view of wireline apparatus of this invention.

Referring to the drawing, the lifting device of this embodiment of the invention has an upper housing which comprises an end fitting 1 which is screw-threaded onto a cylinder 2 which in turn is screw-threaded onto a largediameter body portion 3.

A central rod 4 is secured to the end fitting 1 by means of a screw-threaded connection and extends through the apparatus to a lower portion thereof, where it is screwed into a first piston 5. The piston 5 is slidable in a cylinder 6 and carries seals 21 to prevent escape of fluid past the piston 5. The cylinder 6 is itself slidable within the body portion 3 of the casing, and carries seals 22 to provide fluidtight engagement with the body portion 3.

The cylinder 6 is screw-threaded at its lower end to an end plug 1 8 and is filled with hydraulic fluid. At its upper end the cylinder 6 has circumferentially-spaced ports 7 which communicate with a lower portion of the cylinder 2 below a second piston 8. The piston 8 is slidable in the cylinder 2 and sealed against it by seals 23, and is annular to fit around the central rod 4, having seals 24 to provide a fluid-tight engagement. The piston 6 has an effective lower surface area three times greater than the effective lower surface area of the piston 5.

A compression spring 9 extends between the upper face of the piston 8 and the lower face of the end fitting 1 to bias the piston downwards.

Four ports 10 receive fluid from the cylinder 6 through the ports 7 and extend from the upper portion of the cylinder 6 through the body portion 3 of the casing, these ports 10 being disposed at 90 degree intervals around the body portion 3 and opening into respective radially-directed cylinders 11 behind pistons 1 2. Each piston 12 is slidable in its cylinder 11 and is secured to a respective engagement member, or "slip" 1 3 of hardened steel having a serrated outer face. Each slip 1 3 has a vertical groove in its outer face within which fits a retaining plate 14 with a clearance such that the slip 1 3 can move in and out of the body 3 past the plate 14.A compression spring 1 5 extends between the plate 14 and the piston 12 to bias the piston, and hence the slip 13, into the body 3. The plate 14 is fixed on the body 3 by screws 1 6.

In use, the end fitting 1 is secured by its screw-threaded projection 1 7 to a series of jars the uppermost of which is connected in conventional fashion to a stem and rope socket and thence to a wireline. The end plug 1 8 is screw-threaded to a conventional fishing tool, and the entire resulting wireline assembly is passed down the interior of a cylindrical tubing extending within a borehole from the surface. There the fishing tool is connected to an item of equipment which is to be retrieved and withdrawn to the surface.

A lifting force is applied to the wireline and this is transferred, through the end fitting 1 and central rod 4 to the first piston 5, moving the piston 5 upwards in the cylinder 6. This displaces hydraulic fluid from the cylinder 6 through the ports 7 to the ports 10, pushing the pistons 1 2 radially outwards against the bias of the springs 1 5 and causing the slips 1 3 to engage the internal wall of the casing, locking the body portion 3 against the casing.

When the pistons 1 2 are fully extended, fluid can no longer pass through the ports 10 and is therefore displaced from the cylinder 6 through the port 7 into the cylinder 2, where it pushes the piston 8 upwards, taking with it the cylinder 6 and end plug 1 8 and thus lifting the fishing tool and its load. Since the effective surface area of the piston 8 being acted on by the hydraulic fluid is greater than the effective surface area of the piston 5, the piston 8 travels only one-third as far as the piston 5 but exerts a force three times as great as the applied force on the wireline.

Thus, for example, an applied force of 300 kg on the wireline is translated into a lifting force of 900 kg on the fishing tool.

If the item being lifted continues to exert heavy resistance the piston 5 will come to the end of its travel at the top of the cylinder 2, having moved, say, 30 cm; the piston 8 will then have moved 10 cm. The applied force on the wireline is then relaxed and the springs 9 and 1 5 return the piston 8 and pistons 1 2 to their original positions, taking the slips 1 3 out of engagement with the tubing.

The result of this is that the body portion moves upwards by 10 cm and the lifting device is ready to repeat is performance.

The process is continued until the item being lifted is released and the wireline is then capable of lifting it directly to the surface.

The lifting device of this embodiment therefore provides a means of increasing the effect of an applied force on the wireline so that forces greater than the breaking force of the wireline can be applied to An item being lifted from the wellhead.

Modifications and improvements may be made without departing from the scope of the invention.

Claims (10)

1. A lifting device comprising a first piston having means for connection to lifting means and movable in a first cylinder, a second piston having means for connection to equipment to be lifted and movable within a second cylinder, the first and second cylinders being in fluid communication and the second piston having a greater effective surface area than the first piston, and means for locking at least one of the first and second cylinders against movement, the arrangement of fluid communication between the first and second cylinders being such that movement of the first piston within the first cylinder produces movement of the second piston within the second cylinder.

2. A lifting device according to Claim 1, wherein the first cylinder extends within the second cylinder.

3. A lifting device according to Claim 1 or 2, wherein the second piston is secured to the first cylinder so as to be movable therewith.

4. A lifting device according to any one of the preceding Claims, wherein at least one of the first and second pistons is spring-biassed downwardly.

5. A lifting device according to any one of the preceding Claims, wherein the locking means comprises pistons movable within cylinders disposed radially of said first and second cylinders.

6. A lifting device according to Claim 5, wherein said radially-disposed cylinders are in fluid communication with the first cylinder so that the pistons in the radially-disposed cylinders actuate in response to movement of the first piston in the first cylinder.

7. A lifting device according to Claim 6, wherein the pistons in the radially-disposed cylinders are actuated by movement of the first piston in an upward direction prior to movement of the second piston.

8. A lifting device according to Claim 1, wherein the first and second cylinders are coaxial and the first piston is secured to a lower end of an axially-extending rod which passes through the first and second cylinders and which has an upper end carrying the means for connection to the lifting means.

9. A lifting device according to Claim 8, wherein the second piston is annular and is disposed around said axially-extending rod in fluid-tight engagement therewith.

10. A lifting device substantially as hereinbefore described with reference to and as shown in the accompanying drawing.