GB2330392A - Descaling pipes with liquid jet - Google Patents

Abstract

Scale is removed from lengths of pipe 50 on an oil rig using an upright, tubular de-scaling chamber 16 clamped onto the rig. A pipe 50 is located in the chamber 16 and subjected to high pressure water jets from a hose 38; dislodged scale and water collect in a sump (22 fig.2), and are separated so the water can be reused. The scale may be collected in a transport container (44 Fig 1), and may subsequently be slurrified and injected into subterranean strata. The de-scaling apparatus (10 Fig 1) takes up little space on the deck of the oil rig, and ensures that the contamination remains enclosed throughout the process.

Description

De-scalina Pipes The present invention relates to a method and an apparatus for de-scaling pipes on an offshore rig.

In some oil fields the chemistry of the liquids, in particular the water chemistry, is such that insoluble scales form on the insides of pipes, tubulars, valves and any other tubular structures through which the liquids flow; in this specification all such tubular structures are referred to as pipes. This scale may for example consist primarily of calcium carbonate, calcium sulphate, or barium sulphate, but will often contain at least small quantities of naturally occurring radioactive elements such as radium whose sulphates are insoluble.

Consequently the scale is itself radioactive. It is known to add various chemicals to the liquids in the well to inhibit the formation of the scale; once scale has formed, it is known to remove the pipes and to take them ashore so that the scale can be removed safely. A method that enabled scale to be safely removed from pipes without necessitating transporting the pipes ashore would clearly have advantages.

According to the present invention there is provided a method of removing scale from lengths of pipe on an oil rig, the method comprising clamping a tubular chamber to the rig, the chamber having a longitudinal axis which is at least approximately vertical, and communicating at its lower end with a sump, inserting a length of pipe into the chamber, and then subjecting at least those surfaces of the pipe on which scale is present to high pressure liquid jet treatment to dislodge the scale, so the scale falls into the sump.

The high-pressure liquid jet is preferably a water jet and may be at a pressure of above 200 atmospheres (20 MPa), more preferably above 600 atmospheres, for example 1000 atmospheres (100 MPa). The liquid jet is preferably conveyed into the tubular chamber via a flexible hose, which may be supported on a reel. The dislodged scale along with the water collects in the sump; preferably the method also includes separating the water from the scale and re-using the water in the high-pressure jet treatment, and this separation may be performed within the sump.

The present invention also provides an apparatus for removing scale from lengths of pipe on an oil rig, the apparatus comprising a tubular chamber clamped to the rig, the chamber having a longitudinal axis which is at least approximately vertical, and communicating at its lower end with a sump, and being of such a size that a length of pipe can be inserted into the chamber, the apparatus also comprising means to subject the contents of the chamber to a high pressure liquid jet treatment to dislodge the scale, so the scale falls into in the sump.

Preferably the sump includes means to agitate the contents, and the apparatus also includes means to transfer the contents of the sump to a separation means to separate the water from the scale. The separation means may comprise a vibrating sieve, which is desirably in an enclosed container; the separation means may be within the sump. The water may be returned to the means generating the high-pressure liquid jet, while the separated scale may be stored in a storage tank such as that described in our co-pending patent application GB 9720494.5, from which it may be subsequently discharged, slurrified, and injected into permeable subterranean strata.

The apparatus of the invention does not require a large area of deck space on the rig because the descaling chamber is oriented vertically, and indeed may be clamped to the outside of the rig. The de-scaling chamber is desirably clamped onto the rig using bolts rather than welding so as to avoid the potential hazards associated with welding in the vicinity of oil or other hydrocarbons. Where re-injection is performed the overall process enables scale to be returned to the rock strata from which it originally came, or to adjacent strata, so considerably reducing the risk of spreading any radioactive contamination.

The invention will now be further and more particularly described with reference to, and as shown in, the following drawings in which: Figure 1 shows a perspective view of a de-scaling plant installed on an oil rig; Figure 2 shows a diagrammatic view of the de-scaling plant of Figure 1 to elucidate the flow path for the water; and Figure 3 shows a perspective view, to a larger scale, of the upper part of the de-scaling chamber of the plant of Figure 1, partly broken away.

Referring now to Figure 1, a de-scaling plant 10 is installed on an oil rig 12 which has several decks 13 (only three are shown) and a crane 15. The plant 10 comprises a tubular de-scaling chamber 16 held in a vertical orientation by being clamped by brackets 18 to girders 20 which form part of the rig 12. The lower end of the chamber 16 communicates with a sump 22 which has a vent 23. Below the sump 22 is a pump 24 connected to an outlet pipe 26 which runs alongside the chamber 16, to which it is connected by the brackets 18, and then to a liquid treatment plant 28 which may be enclosed in a standard transport container module 30 as indicated in broken lines. The plant 28 includes a sieve unit 32 to separate water from scale, a filter unit 34, and a high pressure pump 36 (described in more detail in relation to Figure 2). The pump 36 supplies high pressure water to a flexible hose 38 on a reel 40, so the hose 38 can extend down into the chamber 16, and the. reel 40 being supported by a frame 39.

Referring now to Figure 2, the flow of liquid and scale from the chamber 16 into the sump 22, and then via the pipe 26 to the treatment plant 28 is shown diagrammatically. In the plant 28 the water and scale are fed to the sieve unit 32 to pass over vibrating screens so the particles of scale emerge into an outlet duct in which is a screw conveyor 42 which transfers the scale to a sealed transport container 44 outside the module 30 (as shown in Figure 1). The water passes through the screen into a storage tank 46 for clean water. Water from the storage tank 46 then passes through the filter unit 34 to the high-pressure pump 36 which is connected to the hose 38, and which creates a water pressure of about 1000 atmospheres (100 MPa).

In operation, the crane 15 is used to pick up a pipe 50 whose inside is covered with scale, supporting the pipe 50 at one end so it hangs vertically, and then to lower it into the de-scaling chamber 16; similarly the crane 15 is used to remove cleaned pipes 50 from the chamber 16 after they have been de-scaled. The pipe 50 may be supported by screwing a swivel lifting eye (not shown) into an internally-threaded end of the pipe 50.

Referring now to Figure 3, this shows the upper part of the de-scaling chamber 16, partly broken away, supported by a bracket 18. The upper end of the chamber 16 is provided with a hinged lid 52 which can be held closed by clamps 53, and which has a central hole 54 with a seal through which the hose 38, which carries a nozzle 56 at its end, can be inserted. Near the bottom of the chamber 16 is a grid (not shown) on which the pipe 50 rests, and near the top end of the chamber 16 is a conical guide plate 58 defining a central aperture through which the pipe 50 passes, so ensuring it is centred within the chamber 16, and with which the lifting eye may engage to prevent rotation of the pipe 50. Thus with the hose 38 retracted onto the reel 40, the lid 52 can be opened and a pipe 50 lowered into position. The lifting eye is then folded out of the way. The lid 52 is then closed and clamped, and the hose 38 with its nozzle 56 inserted through the hole 54 down into the pipe 50.

High-pressure water is then supplied to the nozzle 56 as it is scanned up and down the inside of the pipe 50, the jet of water dislodging the scale from the pipe wall so it falls down to collect in the sump 22.

It will be appreciated that the de-scaling plant 10 can be modified in various ways while remaining within the scope of the invention. For example the sieve unit 32 and the transport container 44 might be located on the deck 13 next to the sump 22 instead of being on the deck 13 on which the high-pressure pump 36 is located, or may be within the sump 22. In this case the water from the sieve unit 32 would be pumped through a pipe alongside the chamber 16 to the storage tank 46 on the upper deck 13. As mentioned earlier, it is desirable to agitate the scale and water in the sump 22, and a mechanical agitator (not shown) may be provided for this purpose. It may also be necessary to provide more than one transport container 44, the containers 44 being arranged side-byside and all being fed by the same screw conveyor 42.

The duct in which the screw conveyor 42 rotates is desirably enclosed, to ensure that contamination cannot spread onto the rig. The hose 38 might be replaced by coil tubing, so it is less likely to twist; and the nozzle 56 might be a rotating head with needle jet apertures.

It will be appreciated that the descaling process takes place entirely within an enclosure (provided by the chamber 16 and the remainder of the fluid circuit), and the operator is at all times outside this enclosure.

Contamination of the operator or of the rig by radioactive dust is therefore prevented. When all the pipes on a rig have been descaled, the scale may be slurrified and reinjected into a well annulus, and the used water from the tank 46 can be disposed of in the same way.

Claims (8)

1. Claims 1. A method of removing scale from lengths of pipe on an oil rig, the method comprising clamping a tubular chamber to the rig, the chamber having a longitudinal axis which is at least approximately vertical, and communicating at its lower end with a sump, inserting a length of pipe into the chamber, and then subjecting at least those surfaces of the pipe on which scale is present to high-pressure liquid jet treatment to dislodge the scale, so the scale falls into the sump.
2. 2. A method as claimed in claim 1 wherein the pressure is above 60 MPa.
3. 3. A method as claimed in claim 1 or claim 2 also comprising separating the scale from the liquid and reusing the liquid for the high-pressure liquid jet treatment.
4. 4. An apparatus for removing scale from lengths of pipe on an oil rig, the apparatus comprising a tubular chamber clamped to the rig, the chamber having a longitudinal axis which is at least approximately vertical, and communicating at its lower end with a sump, and and being of such a size that a length of pipe can be inserted into the chamber, the apparatus also comprising means to subject the contents of the chamber to a highpressure liquid jet treatment to dislodge the scale, so the scale falls into the sump.
5. 5. An apparatus as claimed in claim 4 also comprising a separation means to separate the liquid from the scale.
6. 6. An apparatus as claimed in claim 3 or claim 4 wherein the separation means is within the sump.
7. 7. A method of removing scale from lengths of pipe substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.
8. 8. An apparatus for removing scale from lengths of pipe substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.