GB2050468A - Method of Severing a Pipe - Google Patents

Abstract

In order to be able to sever safely the tensioned inner pipe 8 of, say, a disused well at a region within an outer pipe 6, the following procedure is adopted. First, access to the inner pipe is gained by severing it about a clamp 10 which holds the inner pipe 8 under tension, the inner pipe 8 is filled with filler material up to a chosen level 16, a charge of a particulate mixture capable of undergoing an aluminothermic reaction is inserted into the pipe 8 and the mixture ignited so that an aluminothermic reaction takes place which produces molten metal that penetrates through the pipe 8 and severs it. It is then safe for a person to enter the well and cut through the outer pipe 6 and inner pipe 8. The well can then be filled in and, if desired, the concrete basin broken up and removed. <IMAGE>

Description

SPECIFICATION Severing of Pipes This invention relates to a method of severing pipes. It is particularly applicable when the pipe to be severed is under tensile stress.

It is often required to fill in an (oil) well after the well has run dry. Typically, the oil well comprises a basin formed of concrete, an outer pipe extending generally vertically through the basin into the ground, an inner pipe, generally axial with the outer pipe, and extending through the basin into the ground, clamping means extending inwards from the accessible end of the outer pipe and holding the inner pipe under tensile stress, and a valve located in the inner pipe intermediate its accessible end and the region thereof held by the clamping means. In order to fill in the well it is necessary to severe the pipes at a level preferably just above the bottom of the basin.

An attempt has been made to do this by first cutting through the outer pipe and then the inner.

This method runs the risk of the tension of the inner pipe being released prematurely with the result that it keels over to one side thereby causing a hazard to the person making the cut.

Accordingly, there is a need for a process which in the situation described above and in other situations enables the pipe under tensile loading to be severed safely.

Accordingly, the invention provides a method of severing a generally vertical, stressed (or tensioned) pipe at a location within an outer pipe, generally axially within which extends the length of the stressed pipe, including the step of conducting an aluminothermic reaction within the inner pipe such that molten metal produced by the aluminothermic reaction penetrated through the inner pipe to its exterior and severs it, or substantially weakens it so as to cause it to be severed by the tensile load acting on it.

The invention also provides a method of fillingin a well including a basin; an outer pipe extending generally vertically through the basin into the ground; an inner pipe, generally axial with the outer pipe and extending through the basin into the ground; and clamping means extending inwards from the accessible end of the outer pipe and holding the inner pipe under tensile stress, which method comprises inserting into the inner pipe filler material (if sufficient of such material is not already present) and then a powdery or particulate mixture capable of undergoing an aluminothermic reaction; and causing the powdery or particulate mixture to undergo the aluminothermic reaction, whereby molten metal produced by the aluminothermic reaction penetrates through the inner pipe to its exterior and severs it below the clamping means, or sufficiently weakens the inner pipe below the clamping means that the inner pipe is severed by the tensile load acting upon it; and cutting through the outer pipe at a location within the basin.

The method according to the invention makes it possible for the inner pipe to be severed so as to remove the tensile stress placed upon it while all personnel are kept remote from the oil well. This, may for example, be done by initiating the aluminothermic reaction electrically or by employing a suitable length of fuse.

The term 'aluminothermic reaction' as used herein indicates an exothermic chemical reaction between a metal oxide and a deoxidising metal.

Typically, the deoxidising metal is aluminium and the metal oxide is iron oxide(s). Such a mixture is available commercially under the trademark Thermit. It is possible, however, to use deoxidising metals (for example magnesium) instead of or in addition to aluminium, and it is also possible to use metal oxides other than iron oxides.

Typically, access to the inner pipe is facilitated by cutting it open above the clamping means. The filler material is typically refractory sand. It is also desirable for the grout to be inserted into the inner pipe, typically up to a level of the floor of the basin. This grout is normally inserted when the well runs dry and before severing the inner pipe above the clamp.

The method according to the invention will now be described by way of example with reference to the accompanying drawing which is a schematic drawing of part of an oil well.

In the drawing is shown the upper part of an oil well and comprises a concrete basin 2 whose mouth is substantially at ground level. The basin may, for example, be approximately two metres deep.

Extending from approximately ground level through the centre of the basin 2 into the ground is an outer steel pipe 6. This pipe is typically about 60 metres long and typically has in internal diameter of about 25 to 30 centimetres. The pipe 6 is vertical. Coaxial with the pipe 6 is an inner pipe 8, also of steel. The pipe 8 extends from about 1 or 2 metres above ground level to about 450 metres below ground level. When the well is originally sunk, the arrangement is that the pipe 8 is stretched and then locked in its stretched state by means of a clamp 10 extending inwards from the top of the outer pipe 6. There is thus a considerable tensile load on the pipe 8. The pipe 8 typically has an internal diameter of about 1 5 centimetres.Located in the pipe 8 intermediate its accessible (above ground) end and the region of its held by the clamp 10 is a manually operable valve 12.

When the well runs dry or otherwise falls into disuse it is typically shut down. This generally involves the step of filling the inner pipe 8 with a suitable grout up to approximately the level indicated by a level 14. This can simply be done by pumping a suitable grout into the pipe through its above-ground end with the valve 12 open.

When it is desired to fill in the well, the following operations are performed in accordance with the invention. First, the inner pipe 8 is cut at a level above the clamp 10 and below the valve 8.

Refractory sand is then inserted into the thus opened pipe 8 until the level of sand is approximately 1 metre to 1-1/2 metres above the floor of the basin. The depth of sand will be approximately the level at which the inner pipe 8 is severed within the outer pipe 6. A charge of Thermit (trademark) mixture is then inserted into the pipe 8. Typically, up to about 10 to 20 kg of Thermit mixture may be employed. a suitable primer may be inserted on top of the charge of Thermit and the Thermit mixture ignited by means well known in the art of conducting aluminothermic reactions. On ignition of the Thermit mixture an aluminothermic reaction takes place which forms molten steel. The temperature of the molten steel is such that it penetrates the pipe 8 at approximately the level 16 and thereby severs the pipe, or substantially weakens it and thereby releases the tension on the pipe 8. When this happens it is safe for the person to enter the basin 2 of the well and cut through the pipe 6 at a level just above the floor of the basin by conventional means (e.g. mechanical cutters, by say, oxy-fuel cutting torches). The inner pipe may then safely be cut at this level. The various lengths of pipe which have been cut off may then be removed from the basin, and, if desired, the concrete is broken up and removed and the basin 2 filled in.

Claims (4)

Claims

1. A method of severing a generally vertical, stressed (or tensioned) pipe at a location within an outer pipe, generally axially within which extends a length of the stressed pipe, which method includes the step of conducting an aluminothermic reaction within the inner pipe such that molten metal produced by the aluminothermic reaction penetrated through the inner pipe to its exterior and severs it, or substantially weakens it so as to cause it to be severed by the tensile load acting upon it.

2. A method of filling in a well comprising a basin; an outer pipe extending generally vertically through the basin into the ground; an inner pipe, generally axial with the outer pipe and extending through the basin into the ground; and clamping means extending inwards from the accessible end of the outer pipe and holding the inner pipe under tensile stress, which method comprises inserting into the pipe filler material (if sufficient of such material is not already present) and then a powdery or particulate mixture capable of undergoing an aluminothermic reaction, and causing the powdery or particulate mixture to undergo the aluminothermic reaction whereby molten metal produced by the aluminothermic reaction penetrates through the inner pipe to its exterior and severs it below the clamping means, or sufficiently weakens the inner pipe below the clamping means that the inner pipe is severed by the tensile load acting upon it; and cutting through the outer pipe at a location within the basin.

3. A method as claimed in claim 2, in which the inner pipe has a valve intermediate its accessible end and the region thereof held by the clamping means, and the inner pipe is initially severed intermediate the said region and the valve so as to facilitate or make possible insertion of filler material and powdery or particular material into the inner pipe.

4. A method as claimed in claim 1 or claim 2, substantially as herein described with reference to the accompanying drawing.