The invention relates to a method for cleaning the upper portion of a well. More particularly it relates to a method for removing scale from the upper portion of a well, wherein a tool with rotatable cleaning head is coupled to a wireline and is moved into the well. The invention also comprises a device for carrying out the method.

Scale in tubulars and wells in connection with petroleum extraction may entail considerable obstacles related to production and function.

Scale has a tendency to form particularly at flow

constrictions and in the upper portion of a well. It is thus a problem that scale for instance in a downhole safety valve may prevent such a valve from being operated as wanted.

It is known to use rotating tools on a so-called wireline- tractor to loosen scale in tubulars and other equipment.

Equipment of this kind has the severe weakness that a part of available electric power which can be supplied via a

relatively long and thin wire is used for driving the

wireline-tractor. Thus there is relatively little power left to drive the rotatable cleaning head.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art. The object is achieved through features which are specified in the description below and in the claims that follow.

There is provided a method for removing scale from the upper portion of a well, wherein a tool with a rotatable cleaning head is coupled to a wireline and is moved into the well, and which method is characterized by comprising:

- providing a roller anchor with a motor for driving the rotatable cleaning head;

- coupling the rotatable cleaning head to the motor;

- letting the tool be moved into the well by its own weight.

By omitting the wireline-tractor and relying on moving the tool into the well by means of its own weight, nearly all the power which can be supplied via the wireline may be used to drive the rotatable cleaning head.

Another advantage is that there is no need to consider a wireline of the same length as when relying on the use of a wireline-tractor. A wireline with larger cross-section can thereby be used, which enables transmission of more electric power .

The method may comprise providing the roller anchor with a hydraulic aggregate in order to be able to move the wheels of the roller anchor towards the well. A pump of the hydraulic aggregate may with advantage be coupled to the motor in such a way that the wheels of the roller anchor is forced towards the wall of the well when the motor is started for driving the rotatable tool.

Control from the surface is thereby limited to simple start and stop of the tool, and feeding and extracting wireline in the well. The method may be carried out by means of a cleaning

equipment for removing scale from the upper portion of a well, wherein a tool with rotatable cleaning head is coupled to a wireline and is movable into the well, and wherein the tool is formed by a roller anchor with driving motor for the rotatable cleaning head and a hydraulic aggregate for

actuating the wheels of the roller anchor towards the well.

The wireline may be coupled to the roller anchor by means of a cable head and a swivel.

The hydraulic aggregate may be driven by the motor and provided with an accumulator.

The rotating tool may be formed by a drill bit. It has been shown that a drill bit is considerably more efficient for removing scale than traditional roller cones, which are arranged to roll against the scale. This is particularly the case when more electric power is available compared to when using wireline-tractors.

The method and the device according to the invention enable a considerably more efficient scale-removal compared to prior art .

In what follows, an example of a preferred method and

embodiment is described, which is visualized in the

accompanying drawing, in which:

Figure 1 illustrates a tool according to the invention.

In the drawing the reference numeral 1 designates a tool for the removal of scale 2 from the upper portion of a well 4.

The tool 1 comprises a roller anchor 6 which is provided with a motor 8 for driving a rotatable cleaning head 10, preferably formed by a drill bit. The rotatable cleaning head 10 is supported in a bearing unit 12.

The roller anchor 6 is coupled to a wireline 14 by means of a cable head 16 and swivel 18 of a type known per se.

The roller anchor 6 is further provided with a hydraulic aggregate 20 which is arranged to be able to move the wheels 22 of the roller anchor 6 out towards the well 4. The, not illustrated, pump of the hydraulic aggregate 20 is driven by the motor 8.

The tool 1 is moved into the well by means of its own weight by paying out wireline 14. When the cleaning operation is about to start, voltage is coupled to the wireline 14, whereby the motor 8 starts and the rotatable cleaning head 10 is caused to pivot relative to the roller anchor 6.

At the same time the motor 8 drives the not illustrated pump of the hydraulic aggregate 20, causing the wheels 22 to be moved towards the well 4 and preventing the roller anchor 6 from pivoting in the well 4.

A roller anchor 6 of this kind is able to take up a

considerable torque, while at the same time it can easily be rolled back and forth in the well 4. Thus, it is possible to control the feeding rate relative to the measured power consumption, which is mainly used for driving the rotatable cleaning head 10. There is thereby achieved an efficient cleaning at the same time as the risk for getting stuck is considerably reduced.