METHOD AND DEVICE FOR REMOVING THE UPPER PORTION OF A WELL

This invention relates to a method for removing the upper portion of a well. More particularly, it relates to a method for removing the upper portion of a well arranged in the ground, in which the upper portion of the well includes at least a portion of a casing extending from the surface down into the ground, and in which, before the removal of the upper portion of the well, the casing is cut at a distance below the surface. The method includes the operations of: arranging a cutting tool, which is arranged to cut the casing at a distance below the surface, on a lifting tool which is arranged to be connected to the casing or a component connected to the casing; lowering the lifting tool together with the cutting tool until the lifting tool abuts against the casing or the component connected to the casing; connecting the lifting tool to the casing or the component connected to the casing; cutting the casing by means of the cutting tool; lifting the portion of the casing out of the ground together with the cutting tool. The invention also includes a device for practising the method.

After a well in the ground has been permanently plugged, it is usual to remove at least the upper portion of the well from the ground at the surface. The surface may be constituted by a seabed.

The well, which may typically be an independent one or belong

to a group of wells in a well frame, most often includes a composite casing, in which several casings of different diameters are positioned one inside the other, and in which an- nuli formed between the casings are normally filled with concrete.

A single or composite casing, which may also include other pipes, for example drive pipe, is termed a casing below. The casing typically extends into the ground from a wellhead which is located, in the case of a submerged well, above the seabed.

According to the prior art the upper portion of the well is removed by first placing a rig vessel above the well. The casing is cut below the seabed, typically by means of a mechanical cutting tool. After the casing has been cut, the cutting tool is removed from the well, after which the lifting equipment of the rig vessel is connected to the casing. The severed upper portion of the casing is then lifted out of the ground.

The prior art method presupposes the use of a relatively large vessel which is provided with drilling equipment, and is, because of repeated connection to the well among other things, relatively time-consuming.

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

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

A method in accordance with the invention for the removal of the upper portion of a well arranged in the ground, in which the upper portion of the well includes at least a portion of

a casing extending from the surface into the ground, and in which, before the removal of the upper portion of the well, the casing is cut at a distance below the surface, is characterized by the method including the operations of:

- arranging a cutting tool, which is arranged to cut the casing at a distance below the surface, on a lifting tool which is arranged to be connected to the casing or to a component connected to the casing;

- lowering the lifting tool with the cutting tool down towards the casing until the lifting tool abuts against the casing or the component connected to the casing;

- connecting the lifting tool to the casing or the component connected to the casing;

- cutting the casing by means of the cutting tool; and

- lifting the severed portion of the casing out of the ground at least together with the cutting tool.

It is advantageous that the cutting tool can be moved relative to the lifting tool after the lifting tool has been placed on the casing or the component connected to the casing.

Alternatively, the cutting tool is placed at a distance below the lifting tool before the lifting tool abuts against the casing or the component connected to the casing.

Advantageously, the cutting tool is secured to the casing before the cutting operation itself is started.

A device for practising the method, also named a cutting device below, includes a cutting tool of a design known per se, for example in accordance with NO 314733. The cutting tool is placed at a distance below a lifting tool. The lifting tool, which is arranged to be connected in a controlled manner to

the casing or a component connected to the casing, is formed in accordance with a technology known per se. The lifting tool is connected to the lifting equipment of a vessel, for example to a crane .

Advantageously, the cutting tool is arranged concentrically relative to the lifting tool, the connecting cable of the cutting tool to the vessel extending via the lifting tool.

In the case of a hydraulic cutting tool using a so-called abrasive fluid, the connecting cable includes hoses for fluid flow and also necessary electrical cables.

In some circumstances it may be advantageous for the lifting tool to be provided with a mechanism which is arranged to move the cutting tool axially relative to the lifting tool.

The lifting tool is provided with a locking mechanism for it to be connected to the casing or a component connected to the casing, typically formed by a wellhead.

In relation to the prior art, the method and device according to the invention provide a substantially simplified procedure for the removal of the upper portion on a well, as several relatively time-consuming operations have been made redundant. The method and device are well suited for use on relatively small vessels with the resulting reduction in cost.

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

Figure 1 shows schematically a cutting tool and lifting tool in accordance with the invention, which are being lowered down to a well on the seabed;

Figure 2 shows the lifting tool abutting against a wellhead;

Figure 3 shows the same as figure 2 but here the lifting tool is connected to the wellhead, the cutting tool is secured to the casing and the cutting operation has been started; and

Figure 4 shows schematically the upper portion of the well lifted out of the seabed together with the cutting tool.

In the drawings the reference numeral 1 indicates a cutting device including a- cutting tool 2 and a lifting tool 4, the cutting tool 2 having been positioned at a predetermined vertical distance, for example in the order of ten metres, below the lifting tool 4.

The cutting tool 2 is constituted by a hydraulic cutting tool, in which there is used an abrasive fluid, exiting under high pressure substantially radially from a rotating nozzle 6.

The cutting tool 2 is supplied with fluid and electrical current, for example for measuring equipment not shown, via a cable 8 extending from the cutting tool 2 up to a vessel not shown. The cutting tool 2 is provided with two securing devices 10.

The lifting equipment 4 is constituted by a wellhead tool, known per se, which is connected to the lifting equipment of the vessel, not shown, by means of a chain 12. The lifting tool 4 is provided with controllable locking dogs 14.

The cable 8 of the cutting tool 2 extends via a guide pipe 16 through the lifting tool 4, the cutting tool 2 hanging concentrically below the lifting tool 4.

A well 20, including a wellhead 22 and a casing 24, extends

from above the seabed 26 down into the ground 28. Here, the wellhead 22 forms the component connected to the casing 24, as it is described in the general part of the specification and in the set of claims .

The wellhead 22 is provided with a connecting portion 30. The pipe bore 32 of the well 20 extends through the wellhead 22 and further within the casing 24.

After the pipe bore 32 has been sealed at the bottom, the cutting device 1 is lowered down towards the well 20, see figure 1. The cutting tool 2 hanging below the lifting tool 4 is moved into the pipe bore 32 until the lifting tool 4, com- plementarily fitting the connecting portion 30, abuts against the wellhead 22, see figure 2.

The securing devices 10 are then urged against the pipe bore 32 to hold the cutting tool 2 in a fixed position relative to the casing 24. The lifting tool 4 is connected to the wellhead 22 by each of the locking dogs 14 being pivoted from its respective inactive position into its active position, in which the locking dog 14 grips under the connecting portion 30, see figure 3.

The casing 24 is cut by means of abrasive fluid flowing at great velocity from the nozzle 6 against the casing 24 while the nozzle 6 is being rotated about its longitudinal axis at the same time .

When the casing 24 has been severed, the cutting operation is stopped. The chain 12 is tightened, thereby pulling, by means of the lifting tool 4 and wellhead 22, the severed portion of the casing 24 out of the ground 28, see figure 4.

The chain 12 may be replaced completely or partially by, for example, a wire, not shown.

It is emphasized that the casing 24 may be constructed as is mentioned under the prior art in the first part of the description.