WO2010070289A2

WO2010070289A2 - Processing apparatus for multiphase hydrocarbon flows

Info

Publication number: WO2010070289A2
Application number: PCT/GB2009/002907
Authority: WO
Inventors: Philip Birch
Original assignee: Heliswirl Technologies Limited
Priority date: 2008-12-16
Filing date: 2009-12-16
Publication date: 2010-06-24
Also published as: GB0822948D0; WO2010070289A3

Abstract

A flow conditioner for conditioning a flow of multiphase hydrocarbon fluids including liquid and gas components, the flow conditioner comprising a flow conduit with a centre line which follows a helical path, the flow conduit having an upstream end and the curvature of the helical centre line increasing in a downstream direction, away from the upstream end. A separator for separating multiphase hydrocarbon fluids including liquid and gas components, the separator comprising a first conduit with a centre line which follows a helical path, a second conduit with a centre line which follows a helical path, the second conduit being arranged laterally adjacent to the first conduit, and communication means for lateral fluid communication between the first and second conduits, and the first and second conduits being arranged so that in use, when multiphase hydrocarbon fluids are passed along the separator, denser components of the fluids undergo swirling flow such that they are flung towards the side of the first conduit remote from the second conduit.

Description

Processing Apparatus For Multiphase Hydrocarbon Flows

The invention relates to processing apparatus for the stabilisation of multiphase fluids flowing into multiphase separation apparatus. In one aspect, it relates to a flow conditioner, and in another aspect it relates to a separator.

In the course of extracting hydrocarbons from producing wells it is common for there to be a multiphase output from the well, with the output material including hydrocarbon liquids (oil), gas and water. The first processing stage of any such produced fluids often involves their separation into liquids and gas, after which the hydrocarbon liquids can be exported by pipeline, truck or ship, and the gas can be either exported separately, or re-injected into the reservoir together with the water. In recent years there has been an increased interest in developing subsea hydrocarbon fields at greater water depths and a greater distances from land. In traditional developments it was common for the gas, oil and water to be carried up by a production riser to a surface process facility, such as a fixed platform or a floating production vessel, where the components are then separated. However, the different phases often become separated and concentrated within the flow lines or production riser giving rise to unstable flows, with accumulations of the denser components (liquid slugs) holding up the flow and reducing field productivity and economics.

In order to avoid the detrimental effects of slug flow, it is becoming increasing desirable to separate the phases as close to the reservoir as possible. This enables the oil to be directly exported by the pipeline as a single phase fluid, the gas to be either exported separately or injected into the reservoir to maintain its pressure, and the water injected into the aquifer below the reservoir. Phase separation is increasingly conducted on the sea bed, close to the wellhead or a gathering station, and in the future may be increasingly conducted within a producing well.

Both locations can still be subject, however, to slug flow. Horizontal producing wells can generate slug flow by changes in gradient along the well path. Poorly distributed gas lift within a well can also give rise to slug flow, as can phase changes within well producing gas condensates. The effect of slug flow on separation equipment, whether located on a surface facility, sub-sea, or down-hole, is to impart a potentially destructive pressure and volume of liquid surge. Slugging is particularly destructive if it enters a centrifugal type of separator, where it can cause structural damage as the flow rapidly changes direction upon commencing its rotational path. Furthermore, the large gas bubbles following the liquid slug can cause the separator to stall. In a gravitational type of separator, the unit often has to be over-sized in order to provide assurance against the liquid and gas surges associated with slug flow, making this type of separator unsuitable for down-hole and many sub-sea locations. Systems have therefore been developed to manage slug flow as a flow enters a separation unit. It is proposed in US 2004/0244983 to provide a system for separating fluids from a hydrocarbon well production fluid mixture at a subsea location. The system has a centrifugal separator for separating gas and liquid, with a liquid outlet connected to a hydrocyclone separator which separates the liquid into oil and water. The authors have identified that gas slugs can pass through the centrifugal separator and into the liquid outlet, where they can adversely affect the operation of the subsequent hydrocyclone separator. A gas slug entering either a centrifugal or a hydrocyclone separator would be likely to alter the gas/liquid ratio therein to a value outside the range required for it to achieve satisfactory performance. Thus, they propose it necessary to "catch" the slug at the entry to the gas/liquid separator and ensure that a gas slug is not passed downstream thereof.

According to US 2004/0244983, a slug detection device is provided upstream of the gas/liquid separator and a liquid flow control valve is provided at the liquid outlet. When a slug is detected, a control means at least partly closes the liquid flow control valve to ensure that the level of liquid in the gas/liquid separator does not fall below prescribed limits and that substantially no gas enters the oil/water separator from the gas/liquid separator. The amount of closure of the valve depends on the size of the slug detected. The proposed system is therefore one of active slug control and requires suitable monitoring and control equipment, and has the disadvantage of requiring constant maintenance. It also involves altering the rate of flow to the oil/water separator and therefore restricting production performance. The above proposal is nevertheless an improvement over earlier systems in which the gas/liquid separator was of a sufficiently large size to allow it to receive a large gas slug without too great a reduction in the liquid level. By providing the separator with a large volume, the volume of a large gas slug can form only a relatively small proportion of the overall separator volume and so the reduction in liquid level can be limited to a manageable amount. Such a system has the advantage of not requiring active flow control, i.e. it is a passive slug control system. However, such a system has the disadvantage of increased size, which is particularly undesirable for subsea installations in view of the need to install them and potentially lift them to the surface for repair or decommissioning.

An alternative approach to slug control is to try and dissipate the slugs upstream of the gas/liquid separator. Proposals of this type are made in the paper "Slug Dissipation in Helical Pipes" by Reyes Ramirez of the University of Tulsa (2000) and "Mechanistic Modelling of Slug Dissipation in Helical Pipes" by Carlos A. DiMatteo R. of the University of Tulsa (2003). These papers propose slug dissipation by providing a pre-separator upstream of a gas/liquid cylindrical cyclone separator. The experimental pre-separator is a helical pipe coiled round a vertical central longitudinal axis with an extremely large helical amplitude. In use, a gas- liquid mixture enters the pipe at the top of the helix, generally perpendicularly to the central longitudinal axis, and flows downwardly and around the coils of the helix. At the bottom of the helical pipe, the flow enters tangentially into the cylindrical cyclone separator. Due to a combination of gravitational and centrifugal forces, a slug is dissipated by separating the phases into a stratified flow that, at the bottom of the helical pipe, enters tangentially into the cylindrical cyclone separator. The bottom outlet of the pre-separator requires that it must be positioned above the cyclone separator. This positioning above the cyclone separator, together with the overall width of the helical coil required for the large helical amplitude, results in a relatively large space requirement, and so the proposal may be of limited benefit compared to simply increasing the size of the cyclone separator itself. In WO 2004/083706 there is proposed well production tubing which is helical. Whilst this proposal addresses the problem of slugs that may block flow along the well production tubing, it does not discuss the idea of conditioning the flow prior to its entry into a subsea separation unit.

A gas/liquid separator has been proposed for use as an in-line device for use at the surface or downhole. The device consists of a straight inner pipe surrounded by a double helical vane which provides a flow path for multiphase fluids. The fluids enter at the base of the device and are forced to rotate by the double helical vane. Liquid flows to the outer wall by virtue of the phase density difference with the gas, which passes through ports in the wall of the inner pipe.

Viewed from a first aspect the invention provides a flow conditioner for conditioning a flow of multiphase hydrocarbon fluids including liquid and gas components, the flow conditioner comprising a flow conduit with a centre line which follows a helical path, the flow conduit having an upstream end and the curvature of the helical centre line increasing in a downstream direction, away from the upstream end. By providing the flow conduit with a curvature which increases, the fluids can make a progressive transition to a swirling flow condition. This can help to impose or maintain stability and prevent any structural damage from an incoming liquid surge.

The flow conditioner may have a longitudinal axis. In preferred arrangements, the centre line of the flow conduit follows said helical path around the longitudinal axis, and at the upstream end of the flow conditioner the centre line is substantially parallel to the longitudinal axis. A flow into the flow conditioner may be generally in alignment with the longitudinal axis of the flow conditioner. For example the centre line of a straight pipe feeding into the flow conditioner may be generally aligned with the longitudinal axis of the flow conditioner. Preferably, the centre line of the flow conduit is substantially coincident with the longitudinal axis.

The arrangement of the longitudinal axis of the flow conditioner being substantially aligned with that of a feed pipe may be contrasted with the Ramirez and DiMatteo proposals discussed above, in which the helical pipe is fed by a pipe perpendicular to the longitudinal axis of the helical coil, resulting in a large space requirement. In preferred embodiments, therefore, the centre line can be aligned with the centre line of a conventional pipe feeding into the flow conditioner. A zero curvature may be provided at the upstream end of the flow conditioner fluid conduit. The curvature then increases in the downstream direction. Thus a transition is provided between the flow in a conventional (normally straight) pipe and a fully developed swirling flow at a downstream region of the flow conditioner.

The curvature of the helical centre line may increase by decreasing the helical pitch in the downstream direction. At the upstream end a very small helix angle (corresponding to a large helical pitch) may be provided, with the helix angle increasing in the downstream direction by increasing the pitch. Preferably, at the upstream end of the flow conduit, the helix angle is less than or equal to 45°, more preferably less than or equal to 40° or 30° or 20° or 10° or 5°. In certain preferred embodiments, the helix angle at the upstream end is substantially zero degrees. In other words, the centre line at the upstream end is substantially straight. The curvature of the helical centre line may increase by increasing the amplitude of the helical centre line in the downstream direction. At the upstream end a very small helical amplitude may be provided, with the helical amplitude increasing in the downstream direction.

In certain embodiments, there may be both a decreasing helical pitch and an increasing helical amplitude in the downstream direction.

The increase in the curvature of the flow conduit may take place over the entire length of the flow conditioner. Alternatively the increase in the curvature of the helical centre line takes place in an upstream portion of the flow conduit, and the flow conduit has a downstream portion, downstream of the upstream portion, in which the centre line has a curvature which is substantially constant or decreases in the downstream direction.

The flow conditioner may be used on a production platform or vessel. It may form part of an onshore producing field, either downhole or on the surface, for example downstream of a well head. It may be located subsea, for example, downhole or on the sea bed, downstream of a wellhead.

In certain preferred embodiments the flow conditioner is arranged with its longitudinal axis generally horizontal, for example at an angle equal to or less than 30° to the horizontal. This arrangement will suit use of the flow conditioner onshore, on the sea bed or at the sea surface on a production platform or vessel. In another aspect of the invention, there may be provided a separator for separating multiphase hydrocarbon fluids including liquid and gas components, the separator comprising a separation unit and a flow conditioner upstream of the separation unit, the flow conditioner being in accordance with the first aspect of the invention, with or without the preferred and optional features discussed above. Thus the flow conditioner may condition the flow upstream of a separation unit.

In use, the flow conditioner can condition multiphase flows including slugs in such a way as to maintain substantially continuous delivery of liquid to the separation unit, thereby minimising problems caused by slug flow.

In the case of the flow conditioner being arranged with its longitudinal axis generally horizontal, the following flow conditioning effects may occur. For example, at low flow rates, the cascading of the flow through the topography of the generally horizontal helix (i.e. the helix with its central longitudinal axis arranged equal to or less than 30° to the horizontal) will break a slug up into bubbles no longer than the helical pitch. At moderate flow rates (moderate flow rates), there is Dean flow (i.e. rotating flow) in which a pair of counter-rotating Dean vortices develop as a result of the presence of a helical axis, and good cross mixing results. Thus slug flow is mixed and broken up into a flow consisting of smaller liquid components and gas bubbles. At still higher flow rates (high flow rates), there is centrifugal flow with a single vortex around the helical axis, with the denser liquid phases being pushed to the outer wall of the flow conduit by centrifugal forces, and the gas being channelled down the inside of the flow conduit, thereby providing a stratified flow and increasing the gas/liquid mix in any cross-section of the flow, resulting in the reduction of slug flow.

Whether arranged horizontally or not, the flow conditioner can be used with various types of separation unit.

In certain embodiments the flow conditioner can feed directly into a gravity separation module, where the size of this module can be reduced owing to the stable nature of the flow exiting the flow conditioning device. In certain other embodiments, the flow conditioner can feed directly into any other design of centrifugal phase separator, where it will ensure liquid levels remain within the design range, and prevent surge pressures from damaging the separation unit. The separator may be an in-line separator. Thus a multiphase flow may be fed first to a flow conditioner, then to a separation unit, with both being in line with a feed pipe.

In certain preferred arrangements, the separator comprises a first conduit arranged downstream of the flow conduit of the flow conditioner to receive, in use, a flow therefrom, the first flow conduit having a centre line which follows a helical path, a second conduit with a centre line which follows a helical path, the second conduit being arranged laterally adjacent to the first conduit, and communication means for lateral fluid communication between the first and second conduits, and the first and second conduits being arranged so that in use, when multiphase hydrocarbon fluids are passed along the separator, denser components of the fluids undergo swirling flow such that they are flung towards the side of the first conduit remote from the second conduit.

Such a separator is of independent patentable significance and, therefore, viewed from a second aspect, the invention provides a separator for separating multiphase hydrocarbon fluids including liquid and gas components, the separator comprising a first conduit with a centre line which follows a helical path, a second conduit with a centre line which follows a helical path, the second conduit being arranged laterally adjacent to the first conduit, and communication means for lateral fluid communication between the first and second conduits, and the first and second conduits being arranged so that in use, when multiphase hydrocarbon fluids are passed along the separator, denser components of the fluids undergo swirling flow such that they are flung towards the side of the first conduit remote from the second conduit.

In use, the denser components of the fluids, i.e. mainly liquid components, accumulate in the first conduit, whilst less dense components, i.e. mainly gas, accumulate in the second conduit. Since the second conduit has a helical centre line, this has the advantage of generating centrifugal flow in that conduit so as to draw , gases into the conduit from the first conduit.

In certain preferred embodiments, the first and second conduits are contained in an imaginary longitudinally extending envelope having a longitudinal centre line, wherein the centre line of the first conduit and the centre line of the second conduit each follows its respective helical path about said longitudinal centre line, and wherein the amplitude of the helical centre line of the first conduit is greater than the amplitude of the helical centre line of the second conduit.

The second conduit may be regarded as being contained in an imaginary longitudinally extending envelope. At least in the preferred embodiments, this envelope is positioned radially inwardly of an imaginary longitudinally extending inner envelope defined by the first conduit. The envelope of the second conduit forms a core around which the first conduit is wound.

Preferably, the first and second conduits are contained in an outer tubular casing. This can provide structural protection.

The communication means for lateral fluid communication between the first and second conduits may be openings between two tubes where they lie alongside each other. Such openings may facilitate movement of separated gas into the second conduit. The openings may be covered by a gas permeable membrane, allowing transport of gas across the membrane and, preferably, blocking liquid and solid transport.

Preferably the second conduit has a smaller inner diameter than the first conduit.

The helical amplitude and/or the helix angle of the first conduit may be variable over its length. The helical amplitude and/or the helix angle of the second conduit may be variable over its length.

The separator may be may be used on a production platform or vessel. It may form part of an onshore producing field, either downhole or on the surface, for example downstream of a well head. It may be located subsea, for example, downhole or on the sea bed, downstream of a well head.

Certain preferred embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Fig. l is a schematic side view of a flow conditioner;

Fig. 2 is a longitudinal cross-sectional view of an end of a flow conditioner;

Fig. 3 is a longitudinal cross-sectional view of part of a flow conditioner;

Fig. 4 is a side view of a separator; Fig. 5 is a cross-sectional view on the lines V-V of Fig. 4;

Fig. 6 is a schematic view of a subsea well production layout; and

Fig. 7 is a schematic cross-sectional view showing a subsea well head and subsea separation apparatus.

Figure 1 shows a flow conditioner 6 in the form of a helical pipe 8. The flow conditioner has an upstream end 39, an upstream, transitional portion 38, and a downstream portion 44. The upstream portion provides a transition from upstream end 39, where the flow is fed from a conventional pipe, to the downstream portion 44. In the upstream portion 38 the curvature of a helical centre line 20 of the helical pipe 8 increases in the downstream direction. In this embodiment the increase is achieved by both reducing the pitch of the helix and increasing the amplitude over the length of the upstream portion 38. In the downstream portion 44 the curvature of the helical centre line is substantially constant. The downstream portion has a downstream end 45.

In use, an unstable multiphase mixture of liquid and gas is fed into the flow conditioner 6 at the upstream end. The multiphase fluids undergo a gradual transition from the flow in a conventional pipe (not shown) from which they are fed to one in which swirl flow has developed. Since the curvature of the helical centre line changes gradually any shock loading effect of a sudden liquid surge can be minimised. At the downstream end 45 of the flow conditioner 6 there is a stable multiphase output which can be fed to a flow separator (examples are described below).

Figure 2 shows another embodiment of a flow conditioner. The drawing shows one end of a flow conditioner 6 in which the helical pipe 8 has a transitional portion 38 defining a flow conduit 42. In the transitional portion 38 the amplitude of the helical centre line 20 reduces towards an end 39 of the flow conditioning unit so as to bring the centreline of the flow conduit generally into alignment with the central longitudinal axis 22 of the helical pipe. The transitional portion 38 then connects to a conventional straight pipe 40 which is arranged with its central longitudinal axis 41 aligned with axis 22. Considering a flow of fluids from the pipe 40 into the flow conditioner 6, the amplitude of the helical centre line of the flow conduit 42 defined by the transitional portion 38 gradually increases in the downstream direction, until the amplitude matches that of the helical centre line 20 in the main part 44 of the helical pipe 8. Thus a gradual transition is provided from a flow conduit with a straight centreline in the pipe 40 to the helical conduit 18 in the main part 44 of the helical pipe 8. Steps in the inside walls at the junction between a helical pipe and a straight pipe, or a sudden change of direction, can be avoided.

The main part 44 of pipe 6 has an end flange 50 which connects to an end flange 52 of the transitional portion 38. At its other end the transitional portion 38 has an end flange 54 which connects to an end flange 56 of the straight pipe 40.

Figure 3 shows a longitudinal cross-sectional view through a helical pipe 8 of a flow conditioner 6. The pipe 8 has a generally circular cross-section and defines a helical flow conduit 18. The flow conduit 18 has a diameter I, which is also the internal diameter of the pipe 8. The conduit 18 has a helical centre line 20 which follows a helical path about a central longitudinal axis 22 of an imaginary envelope 24 which extends longitudinally and has a width W equal to the swept width of the flow conduit 18. The helical centre line 20 has an amplitude A (as measured from mean to extreme) a pitch P and a helix angle θ.

The illustrated helical pipe 8 has a straight axis 22. The amplitude A is shown as constant, although in certain preferred embodiments this could be variable. The helix angle θ (and hence the pitch P) is shown as a constant and in certain preferred embodiments this may be variable.

Figure 4 shows a multiphase separation apparatus 1 comprising a flow conditioner 6 and a separator 2. The flow conditioner has an upstream end adjacent to a transitional portion 38. The separator 2 has a first conduit 48, which is effectively a continuation of the helical pipe 8 of the flow conditioner 6, and a second conduit 53. Conduits 48 and 53 are arranged side by side and each has a helical geometry. The first conduit 48 has a helical centre line 20 and the second conduit 53 has a helical centre line 59. The separation apparatus 1 , including the flow conditioner 6 and the separator, are contained in an outer tubular casing 55.

Referring to Figure 5, this shows the first conduit 48 and the second conduit 53 contained in an imaginary outer cylindrical envelope 60. Communication openings 57 in the conduit walls provide lateral fluid communication between the first and second conduits. The cylindrical envelope 60 has a central longitudinal axis 58. The helical geometries of the first conduit 48 and second conduit 53 are arranged so that the helical centre line 20 of the first conduit 48 is of greater amplitude than the helical centre line 59 of the second conduit 53. In effect the first conduit 48 is radially outwardly positioned relative to the second conduit 53, with respect to the centre line 58 of the outer cylindrical envelope 60, which is also the central longitudinal axis about which the two helical centre lines 20 and 59 revolve. An imaginary inner cylindrical envelope 61 contains the second conduit 53. Point 62 shows the centre of the first conduit 48 and point 64 shows the centre of the second conduit 53.

In use, a multiphase flow 65 enters the separator via upstream end 39 and passes along the flow conditioner 6. From there it passes into the separator 2 where liquid will tend to gather in the first conduit 48 because of its greater density than the gases, which will tend to accumulate in the second conduit 53. Thus, at the downstream end 70 of the separation apparatus 1 the liquid and gas phases are substantially separated into a liquid flow 71 in the first conduit 48 and a gas flow 73 in the second conduit 53.

Figure 6 shows a well production layout comprising a producing zone 72 within a horizontal well, as well as a number of potential positions for separation apparatus 1. A down-hole separation apparatus 1 is shown at 74, a separation apparatus 1 on the sea bed 75 is shown downstream of a wellhead 77 at position 76, and a surface separation apparatus 1 is shown on a production vessel 79 at position 78. A riser 80 leads from the sea bed 75 to the surface. An off-take tanker 82 is shown downstream of the separation apparatus 1 at position 78. A separation apparatus may be provided only at one of positions 74, 76 or

78, or more than one apparatus may be provided, at two of the positions, or at three of the positions. It will be seen that in the case of positions 76 and 78 the separation apparatus 1 is arranged generally horizontally.

It will be seen that in all three cases the separation apparatus 1 is an in-line type of separator. It fits conveniently into a generally linear flow arrangement. Figure 7 shows the use of a flow conditioner 6 feeding into a different type of separator.

Figure 7 shows subsea separation apparatus 1 comprising a subsea separation unit 2 for separating liquid and gas in a multiphase flow. The subsea separation apparatus 1 is fed with a mixture of oil and gas hydrocarbons and water from a subsea wellhead 4, via a flow conditioner 6. The flow conditioner 6 includes a helical pipe 8 having a generally elliptical outlet 10 feeding tangentially into the side of the subsea separator 2. The subsea separator is a centrifugal separator, having a gas outlet 12 at the top, a liquid outlet 14 at an intermediate position and a solids outlet 16 at the base. Other embodiments of a subsea separator may involve a helical flow conditioner feeding a passive separation tank, where the size of the separation tank can be reduced by a reduction of the size of slugs entering the tank.

In use with a centrifugal separator, the multiphase mixture is delivered tangentially to the inside wall of the subsea separator 2 and as it travels round the wall the denser components, i.e. hydrocarbon liquids and water tend to sink whilst gases tend to remain in the upper part of the separator 2. The liquids are discharged from the separator via outlet 14, usually to be passed to a further separator, such as a hydrocyclone, for separation of oil and water. Gas leaves the separator via outlet 12 and may be directed via a gas pipeline to the surface or re-injected into the reservoir. Solids exit via outlet 16.

Claims

CIaims

1. A flow conditioner for conditioning a flow of multiphase hydrocarbon fluids including liquid and gas components, the flow conditioner comprising a flow conduit with a centre line which follows a helical path, the flow conduit having an upstream end and the curvature of the helical centre line increasing in a downstream direction, away from the upstream end.

2. A flow conditioner as claimed in claim 1 , wherein the flow conditioner has a longitudinal axis, wherein the centre line of the flow conduit follows said helical path around the longitudinal axis, and wherein at the upstream end of the flow conditioner the centre line is substantially parallel to the longitudinal axis.

3. A flow conditioner as claimed in claim 1 or 2, wherein the amplitude of the helical centre line increases in the downstream direction.

4. A flow conditioner as claimed in claim 1, 2 or 3, wherein the pitch of the helical centre line decreases in the downstream direction.

5. A flow conditioner as claimed in any preceding claim, wherein the maximum amplitude of the helical centre line is less than or equal to five times the internal diameter of the flow conduit.

6. A flow conditioner as claimed in any preceding claim, wherein the increase in the curvature of the helical centre line takes place in an upstream portion of the flow conduit, and wherein the flow conduit has a downstream portion, downstream of the upstream portion, in which the centre line has a curvature which is substantially constant or decreases in the downstream direction.

7. A flow conditioner as claimed in any preceding claim, wherein the flow conditioner has a longitudinal axis and is arranged with its longitudinal axis at an angle equal to or less than 30° to the horizontal.

8. A flow conditioner as claimed in any preceding claim, wherein the flow conduit has an inner wall which is substantially smooth, in that it has no ribs, grooves, vanes, blades or the like.

9. A separator for separating multiphase hydrocarbon fluids including liquid and gas components, the separator comprising a separation unit and a flow conditioner upstream of the separation unit, the flow conditioner being as claimed in any preceding claim.

10. A separator as claimed in claim 9, the separator comprising a first conduit arranged downstream of the flow conduit of the flow conditioner to receive, in use, a flow therefrom, the first flow conduit having a centre line which follows a helical path, a second conduit with a centre line which follows a helical path, the second conduit being arranged laterally adjacent to the first conduit, and communication means for lateral fluid communication between the first and second conduits, and the first and second conduits being arranged to that in use, when multiphase hydrocarbon fluids are passed along the separator, denser components of the fluids undergo swirling flow such that they are flung towards the side of the first conduit remote from the second conduit.

11. A separator as claimed in claim 10, wherein the first and second conduits are contained in an imaginary longitudinally extending envelope having a longitudinal centre line, wherein the centre line of the first conduit and the centre line of the second conduit each follows its respective helical path about said longitudinal centre line, and wherein the amplitude of the helical centre line of the first conduit is greater than the amplitude of the helical centre line of the second conduit.

12. A separator as claimed in claim 10 or 11 , wherein the first conduit and the second conduits are contained in an outer tubular casing.

13. A separator for separating multiphase hydrocarbon fluids including liquid and gas components, the separator comprising a first conduit with a centre line which follows a helical path, a second conduit with a centre line which follows a helical path, the second conduit being arranged laterally adjacent to the first conduit, and communication means for lateral fluid communication between the first and second conduits, and the first and second conduits being arranged so that in use, when multiphase hydrocarbon fluids are passed along the separator, denser components of the fluids undergo swirling flow such that they are flung towards the side of the first conduit remote from the second conduit.

14. A separator as claimed in claim 13, wherein the first and second conduits are contained in an imaginary longitudinally extending envelope having a longitudinal centre line, wherein the centre line of the first conduit and the centre line of the second conduit each follows its respective helical path about said longitudinal centre line, and wherein the amplitude of the helical centre line of the first conduit is greater than the amplitude of the helical centre line of the second conduit.

15. A separator as claimed in claim 13 or 14, wherein the first conduit and the second conduits are contained in an outer tubular casing.