CLEANING DEVICE

Abstract: A conduit (3) can be cleaned by directing jets (10-14, 25) of abrasive mixture from a pressurised supply at its internal wall from a plurality of nozzles (7, 13, 16) which have no tangential component about the conduit axis. Nozzles preferably include two types, one type (7) which is inclined in one direction to the axis and another type (13) which is inclined in the opposite direction to the axis. When the conduit (3) has an open end, the nozzles (7) directed away from that end are preferably closer to the end than those (13) directed towards it. The density of abrasive mixture supplied by the different types of nozzles is arranged to be different by swirling the mixture and supplying different types of nozzles from different radii in the swirl output chamber (6).

Description: - 1 - CLEANING DEVICE Hard deposits build up on the internal surfaces of process pipework in a number of industries as diverse as brewing, power generation and oil production. It is a particular problem in o l production where deposits such as barium sulphate are formed within the production tubing of producing oil wells at and immediately above the reservoir depth. These deposits reduce the flow area of the tubing, thereby reducing oil flow to the surface. These deposits are very hard. If a mechanical cutter/reamer is used to remove them, damage is frequently caused to the steel pipe itself. The alternative solution at present is to extract the entire length of production tubing to the surface, and to replace it with a new pipe. Because of the depth of some wells this is a laborious and expensive procedure. The present invention is designed to assist the removal of hard deposits from a steel pipe without damaging the pipe itself. Flushing low may be provided to transport the removed deposit to the surface if any fluids being transported by the pipe are not sufficient to do this themselves. Tests have shown that high velocity jets of water will cut through barium sulphate deposits. However to achieve a satisfactory performance pressures of the order of 150 million pascals or higher are required, which is not practical to generate in a deep oil well. Further testing has shown that the addition of low concentrations of solid particles to the flow can dramatically enhance the performance of the jets. This enables the descaling operation to be carried out at much lower pressure, typically at 20 million pascals or less. The invention is therefore suitable for operation in conjunction with conventional oilfield pumping, pipework and other equipment. According to one aspect of the invention there is provided a head for forming jets within a conduit of abrasive mixture from a pressurised supply, the head being formed with a plurality of nozzles which have no tangential component about the conduit axis. In another aspect of the invention, there is provided a method of cleaning a conduit comprising directing jets of abrasive mixture at the internal wall, the jets having no tangential component about the conduit axis. In either aspect, although one or more nozzles can be directed axially and/or radially, is preferred to have different types of nozzles, including one type which is inclined in one direction relative to the axis and another type which is inclined in the opposite direction relative to the axis. Examples of the invention will now be described with reference to the accompanying drawings in which:- Figure 1 is an overall view of a descaling system; Figure 2 is an axial section through the jetting head of Figure 1; Figure 3 is a radial section through the head of Figure 1; and Figure 4 shows the jet pattern which can be achieved by the head of Figure 1. An abrasive mixture, comprising carrier fluid and abrasive particles, is formed and pressurised in a pumping system 21 such as is described in our Patent Publications GB-A-2162778, EP-A-25S424 and EP-A-276219 is fed through a coiled tubing unit 20 to a pipe 2 which is fed down the axis of the pipe 3 "fco be descaled. The abrasive mixture is applied to the bore of the pipe 3 from a special jetting head 1 on the lower end of the pipe 2 which pipe passes through a spacing block 22 for keeping the pipe 2 central within the bore of the pipe 3.. although the symmetry of the spray from the head 1 to be described below may be sufficient to effect the centralising action, rendering the block 22 redundant. The slurry (abrasive mixture) flow enters the jetting head 1 from the supply pipe 2 at one end through a swirling vane 5 (see Figure 2) which imparts rotation to the flow. This causes separation of the constitutents of the flow, with the denser solid particles being concentrated in outer parts of swirl chamber 6. A ring of six nozzles 7 is set into the outer wall 8 of swirl chamber 6. The nozzles 7 are fan-jet nozzles (i.e., the jet is elongated tangentially) which spread the jets of concentrated slurry 10 as a flat sheet 11 with an included angle of spread of 120 degrees to provide a complete ring of coverage of the production tubing 3 and the deposit . In Figure 4 only the flat sheet jets from alternate nozzles in the ring are shown in full. The jetting head 1 is steadily lowered or raised on the pipework system 20. In this way the jets 10 are traversed along the tubing 3 and the impact of the solid particles in the slurry jets 10 on the deposit 4 cause it to be removed from the wall of tubing 3- The nozzles 7 are slightly inclined downwardly, so that the jets 10 tend to bite behind the scale as the head 1 moves progressively down the tubing 3- The central portion of swirl chamber 6 is extended at a smaller internal diameter 12 and supplies another array of nozzles 13. Because the solid particles move to the outer portion of the chamber 10, the flow entering the extended portion of swirl chamber 6 contains very few solid particles. The jets 25 produced by the nozzles 13 are also fan-shaped. These nozzles 13 are slightly inclined upwardly and provide a flushing flow to carry the solid particles from the slurry jets 10 and the deposit which they have removed from the wall of tubing 3 back to the surface. The fan shape of the jets ensures a flushing flow around the full circumference of the tubing 3- It will be seen that the jets from the nozzles 7 and 13 are directed towards each other. The jets from nozzle 7 directed away from the end at which the supply pipe 2 enters the jetting head 1 are closer to that end then the nozzles 13 from which the jets are directed towards that end. In an oilfield application, the tubing is vertical and the abrasive mixture supply comes from and the flushed scale is directed back to the upper open end of the tubing. An additional particle carrying nozzle 16 is fitted into the base of the jetting head 1. A conduit 15 supplies solid particle laden slurry to nozzle 16 from the supply pipe 2 upstream of swirling vane 5 so that although it is of small diameter it has not been stripped of particles by the swirl action. Nozzle 16 produces a generally axially directed jet- 14 in a spreading conical form. The solid particles in jet 14 impact with any of the deposit 4 which extends in towards the centre of the tubing 3 causing it to be removed and opening up a passageway through which jetting head 1 can advance along the tubing 3. The pipework system 20 as shown in Figure 1 is a coiled tubing unit. Alternatively the pipework system might be in the form of pipe lengths which are joined together to extend the length of the system, as for drilling pipe. Both types of pipework system are commonly used in oilfield applications. Other pipework systems might be used, especially where the invention is used to descale pipes in industries other than the oil industry. As shown in Figure 3, the nozzles 7 and 13 are equally spaced around the jetting head 1. This provides a balance of the reaction forces of the jets 10 and 25 and is the preferred arrangement where no rotational motion of the jetting head 1 is provided as in Figures 1, 2 and 3- Since none of the nozzles is directed tangentially, the reaction of the jets provides no rotational drive. Rotational motion can be provided either from the surface or by a downhole motor (not shown). Where rotational motion is provided the centralising guide 22 absorbs the reaction force generated by the jets. In this mode of operation a simple mechanical scraper can orm part of the centralising guide and will remove any small segments of the deposit which are weakened but not removed by the direct action of the jets. - _ - In Figure 4 a single ring of six solid particle carrying nozzles produces fan-shaped flat sheet jets 11, each with an included angle of 120 degrees. The number of nozzles 7 and the angle of the fan sheet 11 are selected based on the n nimum bore of the tubing 3 to be descaled to provide full coverage of the tubing 3. The ring of nozzles could be replaced by a single nozzle producing a hollow cone shaped jet QΓ by multiple rings of nozzles or by multiple hollow cone shaped jets to remove the deposit in progressive steps. The jets with an axially downward direction are useful for separating the deposit from the walls of the pipe 3 whereas the jets with an axially upward direction are useful for flushing the removed deposit up towards the surface and this action may be assisted by any fluids being transported upwards by the pipe at the same time. Where more than one ring of nozzles is used different angles can be used to alter the pattern of attack on the deposit. Where only one ring of nozzles is used individual nozzles can be set at different angles to achieve the same effect. In a similar manner the ring of flushing flow nozzles 13 can include nozzles producing different shapes of jet and also be replaced by more than one ring of nozzles or by a single nozzle for example one producing a cone shaped jet. This also applies to the single forward facing particle carrying jet nozzle 16. This can be replaced by a nozzle producing a different shape of jet or by a number of nozzles. Although flushing flow nozzles 13 are shown in Figures 1, 2 and 3 the flushing flow is not required for all descaling operations. For example they are not necessary when there is a high production flow in the tubing 3« In a similar manner the single forward facing nozzle 16 is not necessary where it is known that the thickness of deposit is not too great. This can particularly be the case where the jetting head 1 is used to carry out regular maintenance as opposed to remedial operations. In an alternative embodiment of the invention the ring of solid carrying nozzles 7 produce straight jets which cut through the deposit down to the underlying wall of the tubing. The jets are then deflected along the wall of the tubing causing the bond between deposit and wall to be broken, and the deposit flakes away from the wall between the tracks of the individual straight jets in the ring. As with the other embodiment alternative nozzle types or multiple rings of nozzles can be employed for the solid carrying nozzles 7 , the flushing flow nozzles 13 and the single forward facing nozzle 7. A particularly advantageous alternative selection for the solid carrying nozzles 7 would be nozzles producing fan shaped jets aligned such the flat sheet is produced in the longitudinal direction of the tubing 3. The use of an abrasive mixture, that is solid particles of abrasive in a carrier fluid, is preferred to the use of fluids alone. The solid particles impact with the brittle deposit, causing it to crack and break off in discrete pieces from the action of carrier fluid of the jet being forced into cracks formed by the impact of the particles. The size of the dislodged pieces of deposit is controlled by setting of the jetting parameters, such as pressure, flow, particle size and other particle properties, and particularly by the concentration of particles in the flow. The solid particles do not need to be of any particular shape to achieve the effect on the brittle deposit, and therefore rounded particles can be used, which will ensure that the underlying pipe is not damaged by the action of the jet. Because of the nature of the solid particles, the effect on the pipe will be confined to a beneficial shot-peening action.

Claims: CLAIMS: 1. A head for forming jets within a conduit of abrasive mixture frcm a pressurised supply, the head being formed with a plurality of nozzles which have no tangential component about the conduit axis. 2. A head as claimed in Claim 1 comprising different types of said nozzles, including one type which is inclined in one direction relative to the axis, and another type which is inclined in the opposite direction relative to the axis. 3. A head as claimed in Claim 2 wherein means are provided within the head to supply abrasive mixtue of different density to the said different types of nozzle. 4. A head as claimed in Claim 3 wherein the head is adapted for connection to the pressurised supply at one end and said means includes a swirl device feeding a chamber, the type of nozzle inclined away from said one end being fed with mixture from the outer portion of said chamber and the other type of nozzle being fed with mixture from the inner portion of said chamber. 5. A head as claimed in any one of Claims 2 to 4 wherein a nozzle of one type is axially spaced from a nozzle of another type such that abrasive mixture ejected from them are directed towards each other. _. 6. A head as claimed in any one of the preceding Claims comprising a further nozzle directed axially. 7. A head as claimed in Claim 6 when dependent on Claim 4 comprising a conduit for feeding abrasive mixture upstream of said swirl device to said further nozzle. 8. A head as claimed in any one of the preceding Claims wherein said nozzle is adapted to produce a jet elongated tangentially. 9. A method of cleaning a conduit comprising directing jets of abrasive mixture at the intended wall, the jets having no tangential component about the conduit axis. 10. A method as claimed in Claim 9 wherein the jets are of different types, a jet of one type being inclined in one direction relative to the axis and a jet of another type beirig inclined in the other direction relative to the axis.

Inventors: GROVE THOMAS WILLIAM, SAUNDERS DAVID HENRY, GROVE, THOMAS, WILLIAM, SAUNDERS, DAVID, HENRY
Applicants: BHR GROUP LTD, B.H.R. GROUP LIMITED
Application year: 1991
Main classification: B24C3
IPC codes: B08B9, B24C3, E21B37, E21B41