GB2359037A

GB2359037A - Cutting apparatus and method

Info

Publication number: GB2359037A
Application number: GB0102989A
Authority: GB
Inventors: Harold Scholes Ashton
Original assignee: Circle Technical Services Ltd
Current assignee: Circle Technical Services Ltd
Priority date: 2000-02-08
Filing date: 2001-02-07
Publication date: 2001-08-15
Also published as: GB0102989D0; GB0002704D0

Abstract

A cutting device having a first outlet 20 for pressurised fluid e.g. water with entrained abrasive and a second outlet 25 for a second fluid e.g. air, oxygen, nitrogen or inert gas. The cutting device shrouds the first fluid in a gas bubble while cutting so that the force of the cutting jet is not dissipated when used underwater e.g for cutting pipes.

Description

2359037 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 "Cutting

Apparatus and Methodu This invention relates to apparatus and a method for cutting using pressurised fluids.

The art of cutting metals using high-pressure water jets is well-known, and has been practised in the oil industry for many years. A typical highpressure water cutting apparatus comprises the jet cut system supplied by Circle Technical Services Limited of Aberdeen, UK. The jet cut system delivers a suspension of abrasive in water at a pressure around 140 to 350 bars to a spray nozzle and at a rate of 40 to 90 litres per minute. The nozzle can be simply held in close proximity to a pipe to be cut by being mounted on a manipulator which can travel around the outer circumference of the pipe and can hold the nozzle in a predetermined orientation in relation to the pipe as it moves. Such manipulators are well known in the art.

2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 As well as being mounted on manipulators which travel on chains around a pipe, the nozzle can be mounted onto a saddle assembly on an ROV, for example for use underwater, or on a T-bar clamp assembly to allow the nozzle to be held against a chain or other such object to be cut.

Internal pipe cutters are also common in the art comprising a sub lowered down a casing or conductor to a desired level and fed with umbilicals carrying abrasive slurry and water at high pressure. The nozzle from which the jet is propelled is held at right angles to the wall of the casing. It is common in the art for such apparatus to cut through several layers of casing during decommissioning of wells etc. Instead of being disposed at 900, the nozzle on the internal pipe cutter can, of course, be disposed at any desired angle, and cap cutters are also known with nozzles oriented axially along the tubular, to cut through a cap which has been set in place occluding the tubular in a previous operation.

Numerous other embodiments are known, principally differing in the manner in which the nozzle is held against the object to the cut, and whether it is placed outside the object or within its bore.

The present inventors have found that a problem with existing water/abrasive cold cutting jets is that when operated underwater, the surrounding fluid 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 through which the high-pressure water jet travels before cutting through the object dissipates the force of the jet. While underwater high- pressure cold cutting jets cut satisfactorily through single layers of pipe, they have some difficulty in cutting through several concentric layers of pipe as are commonly found at or below wellheads in oil wells. The cutting operation is particularly ineffective where the jet has to pass through a fluid or groutfilled annulus.

According to the present invention there is provided a cutting apparatus comprising a source of pressurised first fluid, and an outlet for the first fluid linked to the source, a source of second fluid, and an outlet for the second fluid arranged to eject the second fluid into the vicinity of the outlet for the first fluid.

The two outlets are preferably separate but adjacent.

The second fluid is preferably a gas such as air and the first fluid is preferably a liquid such as water.

In certain embodiments of the invention, a nozzle is provided for the outlet for the first fluid, and the outlet for the second fluid is provided in the same nozzle. In certain other embodiments of the invention, the outlet for the second fluid is provided separately from the nozzle, but in the close vicinity thereof. The apparatus may be provided with 4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 a manipulator to rotate the outlet for the first fluid (and optionally the outlet for the second fluid) in order to move it into different orientations.

Several outlets for each of the fluids can be used, optionally spaced apart from one another.

In certain preferred embodiments of the invention, the outlet for the second fluid and the outlet for the first fluid are concentric, but is sufficient for the outlet for the second fluid to be in the same general vicinity as the outlet for the first fluid. Various other configurations are possible, and in most preferred embodiments of the invention, the second fluid outlet or outlets are generally disposed in a regular pattern around the central axis of the fluid outlet.

The present invention also provides a method of cutting an object, the method comprising ejecting a first fluid under pressure from a first outlet so that the pressurised first fluid cuts the object, and ejecting a second fluid from a second outlet in the same vicinity of the first outlet.

The composition of the first and second fluids is a variable option, and they are preferably different but need not necessarily be different. Typical gases include air, oxygen, nitrogen and other inert gases.

1 2 3 4 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 In a preferred embodiment wherein the first fluid is water and the second fluid is air, the pressurised water is preferably ejected at a pressure of between 10 to 10000 psi, and the pressurised air is preferably ejected at a pressure of 10-5000psi, and preferably around 400psi.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings in which:- Fig. 1 is a side sectional view of a casing string at a wellhead with cutting apparatus disposed therein; Fig. 2 is a plan sectional view through the line 2'2' in Fig. 1; Fig. 3a, 3b and 3c are end sectional views through alternative nozzles of the Fig. 1 and Fig. 2 apparatus; and Fig. 4 shows a side sectional view of a second embodiment of cutting apparatus.

Referring now to the drawings, Fig. 1 shows a casing string at an inactive wellhead (not shown) to be decommissioned, the casing string comprising an outer large bore liner 1, a medium bore tubular 2 concentric with and located inside the liner 1 and a small bore tubular 2.

tubular 3 located inside the medium bore The casing 1 and medium and small bore tubulars 2 and 3 respectively are connected together (not shown) as is known in the art. Water fills the 6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 bores of small and medium bore tubulars 2 and 3, and the annulus between tubular 2 and liner 1 is grouted as is conventional in the art.

A cutter 10 is disposed in the bore of the inner tubular 3, and has a manipulator 12, a head 15 and a nozzle 20. The head 15 is rotatable about the central axis of the cutter 10 by the manipulator 12 so that the nozzle 20 can circumscribe a 3600 arc around the inner surface of the tubular 3. In this example, the nozzle 20 is directed at 900 towards the inner surface of the tubular 3. The cutter 10 has a hose (not shown) delivering pressurised water and (optionally) an abrasive material to the head 15 and from there to the nozzle 20. A further hose (not shown) delivers pressurised gas (e.g. air) to a gas delivery hose 25 in the head 15. The gas delivery hose 25 has an outlet that is adjacent to the nozzle 20, and is oriented in the same direction. Pressurised gas emanating from the outlet of the hose 25 is expelled in the same direction as pressurised water and abrasive expelled from the nozzle 20. The gas delivery hose 25 rotates with the head 15.

Pressurised gas expelled from the outlet of the gas delivery hose 25 creates a gas pocket 30 in the vicinity of the outlet 20 for the pressurised water, allowing the pressurised water jet 21 to pass through the annular space between the tubulars 2 and 3 unhindered by dissipation effects due to the surrounding water, since the pressurised gas pocket 7 1 2 3 4 5 6 7 8 9 10 11 12 13 14 is 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 has displaced the water from that annulus in the vicinity of the nozzle 20. The displacement of the water from the area of the nozzle 20 allows the water jet 21 to cut through tubular 2, grout and outer liner 1 without dissipation of the force of the water jet which wouldnormally occur when travelling through a liquid medium.

Fig. 3 shows different designs of nozzle cross section with "WAX' indicating the outlet for the water jet and "gas" indicating the outlet or outlets for the gas delivery hose 25. It can be seen that it is not necessary to surround the water jet outlet with gas jet outlets completely; it is sufficient to generate the gas pocket 30 in the general vicinity of the water jet outlet; this displaces the water enough to reduce the dissipation effects on the cutting jet. Note that it is also preferable to have separate outlets and hoses connected to separate pressurised reservoirs, but the outlets can be simply provided on the reservoirs, which can be positioned at the cutting face if desired on simple embodiments.

A further example of the invention is shown in Fig. 4, which shows a relatively simple embodiment of the invention. In the Fig. 4 embodiment, a body 100 is lowered into casing on a winch (not shown) and is centralised in the casing by centraliser/clamp arms 101. The body 100 carries hoses for water and abrasive mixture 119 and for gas 125. The separate water 119 and gas 125 hoses are connected to a 8 1 2 3 4 5 6 manifold 114 having a rotating head 115 and a nozzle 120.

Favourable designs of nozzle for this embodiment are shown in Fig. 3a, b and c.

7 8 9 10 11 12 13 14 15 16 17 Introduction of the gas flow around the water column creates a protective shroud or gas pocket that displaces the water from the adjacent area preventing dissipation of the force from the jet of water and abrasive, enabling the water jet 121 to cut through several layers of tubular remote from the end of the nozzle 120.

modifications and improvements can be incorporated without departing from the scope of the invention.

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Claims

Claims

Cutting apparatus comprising a source of first fluid, and an outlet for the first pressurised fluid linked to the source, a source of second fluid, and an outlet for the second fluid arranged to eject the second fluid into the vicinity of the outlet for the first fluid.
2. Cutting apparatus as claimed in claim 1, wherein the two outlets are in close proximity.
Cutting apparatus as claimed in claim 1 or claim 2, wherein the second fluid is a gas and the first fluid is a liquid.
4. Cutting apparatus as claimed in any preceding claim, wherein the outlet for the first and second fluids comprises a nozzle.
5. Cutting apparatus as claimed in any preceding claim, having a manipulator to move at-least one of the fluid outlets.
6. Cutting apparatus as claimed in any preceding claim, having more than one outlet for each of the fluids.
Cutting apparatus as claimed in claim 6 wherein the outlets for each fluid are spaced apart from one another.
8. Cutting apparatus as claimed in any preceding claim, wherein the outlet for the second fluid and the outlet for the first fluid are concentric.
A method of cutting an object, the method comprising ejecting a first fluid under pressure from a first outlet so that the pressurised first fluid cuts the object, and ejecting a second fluid from a second outlet in the same vicinity of the first outlet.
10. A method as claimed in claim 9, wherein the second fluid displaces surrounding fluid from the vicinity of the jet of first fluid as it is ejected from the first outlet.
11. A method as claimed in claim 9 or claim 10, wherein the first and second fluids are different.
12. A method as claimed in any of claims 9-11, wherein the second fluid is selected from the group comprising air, oxygen, nitrogen and other inert gases.
13. A method as claimed in any one of claims 9-12, wherein the first fluid is a liquid and the second fluid is a gas.
14. A method as claimed in any one of claims 9-13, wherein the pressurised first fluid is ejected at a pressure of between 10 to 10000 psi.

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15. A method as claimed in any one of claims 9-14, wherein the second fluid is ejected at a pressure of 105000psi.
16. A method as claimed in claim 15, wherein the second fluid is ejected at a pressure of around 400psi.
17. A method as claimed in any one of claims 9-16, wherein the second fluid is ejected at a lower pressure than the first fluid.
18. A method as claimed in any one of claims 9-17, carried out in a liquid environment.

A method of cutting an object as hereinbefore described.

2 0. Cutting apparatus as hereinbefore described with reference to any one of the accompanying drawings.