Separator and Method of Separation

Abstract

A method of separating a multiphase fluid, the fluid including a relatively high density component and a relatively low density component, that includes introducing the fluid into a separation region; imparting a rotational movement into the multiphase fluid; forming an outer annular region of rotating fluid of predetermined thickness within the separation region; and forming and maintaining a core of fluid in an inner region. Fluid entering the separation vessel is directed into the outer annular region and the thickness of the outer annular region is such that the high density component is concentrated and substantially contained within this region, the low density component being concentrated in the rotating core. A separation system employing the method is also provided. The method and system are particularly suitable for the separation of solid debris from the fluids produced by a subterranean oil or gas well at wellhead flow pressure.

Claims

1. A subsea processing assembly comprising: a wellhead assembly through which fluids are produced from a subterranean well; a separator assembly comprising a fluid inlet connected to the wellhead assembly for receiving fluids produced from the well, the separator assembly being operable at well pressure to remove well debris entrained in the fluids to produce a solids rich phase and a fluid phase, the separator assembly comprising a fluid outlet for the fluid phase; and a choke assembly comprising an inlet connected to the fluid outlet of the separator assembly.

2. The processing assembly of claim 1, wherein the separator assembly is located subsea.

3. The processing assembly of claim 1, wherein the separator assembly is located on a platform, the processing assembly further comprising: a fluid receiving assembly for receiving fluids produced from a subterranean well, the separator assembly comprising a fluid inlet connected to the fluid receiving assembly for receiving the fluids produced from the well.

4. A processing assembly comprising: a fluid receiving assembly for receiving fluids produced from a subterranean well; a separator assembly comprising a fluid inlet connected to the fluid receiving assembly for receiving fluids produced from the well, the separator assembly being operable at well pressure to remove well debris entrained in the fluids to produce a solids rich phase and a fluid phase, the separator assembly comprising a fluid outlet for the fluid phase; and a choke assembly comprising an inlet connected to the fluid outlet of the separator assembly.

5. The processing assembly of claim 4, further comprising a wellhead assembly through which fluids are produced from the subterranean well.

6. The processing assembly of claim 4, wherein the wellhead assembly is located subsea.

7. The processing assembly of claim 4, wherein the separator assembly is located on a platform.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Embodiments of the present invention will now be described, by way of example only, having reference to the accompanying drawings, in which:

[0113] FIG. 1A is a schematic representation of the flow patterns of the components of a multiphase fluid stream in the method of the present invention;

[0114] FIG. 1B is a schematic representation of alternative flow patterns of the components of a multiphase fluid stream in the method of the present invention;

[0115] FIG. 2 is a longitudinal cross-sectional view through a separator system according to a first embodiment of the present invention;

[0116] FIG. 3A is a longitudinal cross-sectional view through a separator system according to a second embodiment of the present invention;

[0117] FIG. 3B is a longitudinal cross-sectional view through a separator system according to a third embodiment of the present invention;

[0118] FIG. 4 is a longitudinal cross-sectional view through a separator system according to a fourth embodiment of the present invention;

[0119] FIG. 5 is a longitudinal cross-sectional view through a separator according to a fifth embodiment of the present invention;

[0120] FIG. 6 is a partial cross-section view through a separator according to a sixth embodiment of the present invention;

[0121] FIG. 7 is a cross-sectional view through the inlet and separation regions of a separator according to a seventh embodiment of the present invention;

[0122] FIG. 8 is an enlarged cross-sectional view of the fluid inlet region of the separator of FIG. 7;

[0123] FIG. 9 is a representative view of a subsea processing assembly using a separator assembly in accordance with various embodiments: and

[0124] FIG. 10 is a representative view of a platform processing assembly using a separator accordance with various embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0125] References to upwards and downwards as used herein refer to the assemblies with longitudinal axes in the vertical orientation as shown in the accompanying figures. It will however be understood that non-vertical orientations may also be applied and the aforementioned terms are to be construed accordingly.

[0126] Referring to FIG. 1A, there is shown a schematic representation of a typical fluid flow pattern within the separation region of the method of the present invention. A multiphase fluid 2 is introduced into a vertically oriented separation region 4 through a single rectangular tangential inlet 6. The inlet 6 is at an angle to the longitudinal axis of the separation region 4, such that the incoming fluid 2 is directed against the wall of the separation region in a helically descending flow pattern 8. The general direction of fluid flow is indicated by the arrow in FIG. 1. The helical flow pattern establishes an outer annular region 10 adjacent the wall of the separation region 4 within which is disposed a core region 12. The components of the multiphase fluid having a higher density are concentrated in the outer annular region 10, while the lower density components migrate to and are collected in the core region 12. An interface 14 is established between the core region and the outer annular region. For example, when the multiphase fluid comprises solids, liquids and gases, the outer annular region 10 is essentially a rotating wall of liquid, with entrained solids and some entrained gas bubbles. In contrast, the core region 12 is composed of gas, with some entrained liquid droplets. A rapid exchange of liquid and gas will occur across the interface 14 between the core region and the annular region, as the fluid descends within the separation zone. As will be seen from FIG. 1, the interface 14 is convex in shape in the downstream direction of flow.

[0127] As shown in FIG. 1A, the helical flow pattern followed by the incoming fluid has a pitch such that the fluid completing its first revolution passes below the incoming fluid entering through the inlet 6. In this way, the incoming fluid avoids colliding with the rotating fluid already within the separation region 4. This serves to quickly and efficiently establish the outer annular region at the thickness predetermined by the dimensions of the inlet 6.

[0128] As also shown in FIG. 1A, the inlet 6 is disposed some distance from the upper end of the separation region 4. In this way, high density fluid and entrained solids splashing from the outer annular region 10 are caused to drop back into the fluid stream and become entrained in the fluid circulating in the outer annular region 10. In this way, the erosion of the top of the vessel wall containing the separation region 4 is minimised.

[0129] FIG. 1B shows a similar representation of fluid flow patterns to that of FIG. 1A. Features of FIG. 1B shared with FIG. 1A are indicated using the same reference numerals. In FIG. 1B, the multiphase fluid is divided into two streams 2 and 3 and is caused to enter the separation region 4 through two opposed rectangular inlets 6 and 7. Each inlet 6 and 7 is arranged tangentially to the wall of the separation region 4. The inlets 6 and 7 are angled such that the incoming fluid from the inlet 7 flows below and under the fluid stream 2 entering through the inlet 6, in order to avoid collision between the fluid streams 2 and 3. It will be appreciated that three or more inlets may be arranged, applying a similar approach to that of FIG. 1B, such that multiple fluid streams are introduced into the separation region 4 with minimal or no collision between the incoming fluid streams.

[0130] Referring to FIG. 2, there is shown, in vertical cross-section, a separator system according to one embodiment of the present invention. The separator system, generally indicated as 102, comprises a generally cylindrical, vertically oriented separator 104, having a cap 106 mounted on the upper end of the separator by means of a flange 108 and bolts 110. A tapered solid concentrator 112 is secured to the lower end of the separator 104 by means of flanges 114 and bolts 116. As shown in FIG. 2, the solid concentrator 112 has a conical inner portion. The angle of the conical section will be determined by the properties of the fluid being processed. Cone angles in the range of from 5 to 20 from the longitudinal axis of the separator are typical for the separation of a fluid stream comprising crude oil, water and solids.

[0131] The separator 104 has a generally cylindrical bore running therethrough, extending in its upper portion into the cap 106 and, in its lower portion, partially into the solid concentrator 112. The remaining portion of the solid concentrator 112 is formed with a tapered bore, decreasing in cross-sectional area in the downwards direction and opening into a slurry container 118 mounted to the lower end of the solid concentrator 112 by means of flanges 120 and bolts 122. The combined bores of the cap 106, separator 104, solid concentrator 112 and slurry container 118 form a separation region. The components forming the separation region are of sufficiently wear resistant material to avoid excessive erosion of the walls or may be lined or sleeved in such material.

[0132] The cap 106 is provided with a feed pipe 124 communicating with a rectangular inlet 126 in the cap. The feed pipe 124 and the rectangular inlet 126 are arranged at an acute angle to the longitudinal axis of the separator and tangentially to the wall of the cap 106. The angle of the feed pipe 124 and the inlet 126 will be determined by the properties of the fluid stream and the separation duty to be performed. A typical angle for the feed pipe 124 and inlet 126 is from 5 to 20, measured from a line perpendicular to the longitudinal axis of the separator 104.

[0133] The dimensions of the inlet opening will also be determined by the fluid stream and the separation duty. For a fluid stream comprising a viscous crude oil, water and sand particles, the inlet 126 will be sized to provide a fluid inlet velocity of from 1 to 5 m/s. The relative dimensions of the inlet opening, that is its aspect ratio, are determined by the fluid properties and the separation and the required flow pattern within the separator 106. In particular, the aspect ratio of the inlet 126 will affect the thickness of the outer annular region, in which the heavier components will concentrate.

[0134] A fluid outlet pipe 128 extends co-axially from the closed end of the cap 106 down into the solid concentrator 112. At its upper end, the fluid outlet pipe 128 communicates with an outlet 130 in the cap 106, to which is connected to the inlet of a production fluid choke 132 of conventional design, for example a plug-and-cage choke. The outlet of the production fluid choke 132 is connected to a fluid line 134 leading to downstream fluid processing equipment. The lower end of the fluid outlet pipe 128 coincides generally with the junction between the separator 104 and the solid concentrator 112 and is closed. The lower end portion of the fluid outlet pipe 128 comprises a plurality of fluid ports 136 extending in a radially outwards direction at a tangent to the outer surface of the fluid outlet pipe 128.

[0135] A vortex control assembly 138 is provided and mounted on the lower end of the fluid outlet pipe 128, and comprises a fluid guide 140 in the form of an inverted cone to provide a vortex flow foil. The fluid guide 140 acts to disseminate the upwards flowing vortex. This induces a curved flow path allowing fluid to circulate and enter the tangential ports 136 without fluid suction arising. The fluid guide 140 also forces the heavier components outwards, thus preventing a premature widening of the outer annular region and pushing the interface 125 radially outwards. This further enhances separation of the components of the fluid stream.

[0136] The slurry container 118 comprises a generally cylindrical bore of larger internal diameter than the diameter of the lower end of the tapered bore in the solid concentrator 112. A perforated cage 142 having an internal diameter corresponding to that of the lower end of the tapered bore in the solid concentrator extends co-axially through the slurry container 118 and forms an annular region 144 in the slurry container. The perforations 146 in the cage 142 are arranged tangentially and connect the bore of the cage 142 with the annular region 144. A tangentially arranged fluid outlet is provided in the lower portion of the annular region 144 of the slurry container 118 and connected to the inlet of a slurry choke 148 of conventional design, for example a stem-and-orifice choke. The outlet of the slurry choke 148 is connected to a slurry line 150 leading to the downstream slurry processing equipment.

[0137] The perforated cage 142 is connected at its lower end to an outlet 152 in the slurry container 118, which is in turn connected by a hydraulic or manual ROV valve 154 to a debris line 156, through which debris collected in the system may be collected and removed.

[0138] In operation, a multiphase fluid stream comprising gas, one or more liquid phases, and solid particles ranging from sand to well debris is fed through the feed pipe 124 to the rectangular inlet 126 in the cap 106. Such a multiphase fluid is typical of the stream produced from a subterranean well. The fluid stream enters the separation region in the cap 106 and flows in a helical pattern downwards within the cap 106 and separator. The liquid and solid phases present in the fluid stream are substantially confined to flow in an annular region adjacent the wall of the cap 106 and separator. A core region consisting essentially of gas is maintained within the separation region, the interface between the core region and the annular region being shown by the dotted line 125 in FIG. 2. As rotating liquid stream descends within the separator 104, entrained gas is caused to pass into the gas core. Liquid droplets and any solid particles that may be entrained within the gas core are caused to move in the opposite direction and enter the liquid annular region.

[0139] As the liquid stream in the annular region descends, it loses angular momentum, resulting in the annular region becoming larger in cross-section as the separator 104 is descended and the core region smaller in cross-section, until the liquid in the annular region extends across the bore of the separator. This action forms the convex shape of the interface shown in FIG. 2 and in more detail in FIGS. 1A and 1B. The continued rotation of the liquid causes the more dense phases, including the solid particles, to collect at the wall of the separator, while the less dense liquid and gas phases will move towards the central axis of the separator 104.

[0140] Clean fluid is removed from within the separator 104 through the fluid ports 136 in the lower portion of the fluid outlet conduit 128. This fluid will comprise both the less dense liquids from the annular region, as well as gas displaced downwards from the core region. This combined fluid stream exits the conduit 128 through the outlet 130 in the cap 106 and passes via the production fluid choke 132 to the fluid line 134 for further processing.

[0141] The rotational action of the liquids remaining in the separator can create a vortex, which will have the effect of causing fluid flow to be drawn up from the rotating slurry fluid and reducing the separation of the phases, in particular the separation and gradation of the solid particles. The vortex control assembly 138, in particular the vortex flow foil 140, on the lower end of the fluid outlet conduit 128 prevents the vortex from drawing slurry from the slurry separation region and passing upwards into the region around the ports 136 in the fluid outlet conduit 128. The vortex flow foil 140 also acts to push the downward fluid flow outwards towards the wall of the separation region, further enhancing solids separation.

[0142] From the separator 104, fluid passes into the solid concentrator 112. The cross-sectional area of the flowpath of the fluid is reduced along the length of the solid concentrator 112 by the combined effects of the tapered bore of the concentrator 112 and the conical fluid guide 140, causing the fluid to become concentrated in the solid particles and form a slurry.

[0143] The slurry passes to the central perforated cage 142 of the slurry container 118, where the vortex acts to rotationally agitate the fluid and entrained solids. Fluid and smaller solid particles pass outwards through the perforations 146 in the perforated cage 142 as the slurry descends within the slurry container and are removed from the annular region 144 through the outlet to pass to the slurry choke 148. Solid debris remains within the perforated cage 142 and leaves the slurry container 118 through the lower outlet 152. Depending upon the amount of debris in the stream being processed, the hydraulic or manual ROV valve 154 may be left open, to provide a continuous flow of debris, or may be opened intermittently, for example by a remote operated vehicle (ROV), to empty the bore of the slurry container when sufficient debris has been collected. The ROV may be provided with a receptacle for receiving the solid debris for removal.

[0144] Referring to FIG. 3A, there is shown an alternative embodiment of the separator system of the present invention. The components of the system of FIG. 3A corresponding to those of the system of FIG. 2 are indicated using the same reference numerals. The general manner of operation of the system of FIG. 3A is largely the same as that of FIG. 2. Accordingly, to avoid repetition, only the differences in construction and detailed operation between the systems of FIGS. 2 and 3A will be described.

[0145] The system of FIG. 3A comprises a slurry container 118 mounted directly on the lower end of the separator 104, the separation region being formed by the combined generally cylindrical bores of the cap 106, the separator 104 and the slurry cage 118. The lower end of the fluid outlet conduit 128 is closed with a conical cap 140. A slurry collection cage 172 extends co-axially upwards within the slurry container 118. A plurality of tangential perforations 176 are formed in the slurry collection pipe 172. The lower end of the slurry collection cage 172 connects with a slurry outlet 178 in the lower end of the slurry container 118, which in turn connects with a slurry choke 148 and slurry line 150. A tangential debris outlet port 180 is disposed in the wall of the slurry container 118 adjacent its end, which is connected to a hydraulic or manual ROV valve 154 and a debris line 156.

[0146] In operation, the separator system of FIG. 3A provides an alternative means of solid concentration and solid collection. The cross-sectional area of the downstream end of the bore within the separator 104 available for the flow of fluid is reduced by means of the conical cap 174 on the slurry collection cage 172, causing an annular concentration of solids within the fluid. This causes the concentration of the solid particles within the fluid phase as the stream descends from the separator 104 to the slurry container 118 forming a region of relatively still fluid, allowing solid particles to settle and form a concentrated slurry. Fluid is removed from the slurry container 118 by passing through the tangential perforations 176 in the slurry collection pipe 172.

[0147] Referring to FIG. 3B, there is shown an alternative arrangement to that of FIG. 3A, but employing the same principle for the collection and removal of solid particles using a slurry collection cage 172. The assembly of FIG. 3B employs a generally cylindrical separator 104, the slurry container having a diameter substantially the same as that of the separator 104. To provide a constriction in the downward fluid flowpath, the slurry collection cage 172 has its upper end closed by a conical cap 174. A vent port 175 extends vertically through the conical cap 174. The vent port 175 in the conical cap 174 provides an outlet for fluid displaced from the slurry container 118.

[0148] In the slurry container 118, fluid and solid particles are caused to try and concentrate on the separator axis and to flow through the tangential slots 176 and enter the slurry collection cage 172, from where they are discharged through the slurry outlet 178, via the slurry choke 148 into the slurry line 150. Debris and very coarse solids in a fluid slurry are removed from the slurry container through the debris outlet 180 and via the hydraulic or manual ROV valve 154 into the debris line 156.

[0149] The arrangements of FIGS. 3A and 3B offers advantages over that of FIG. 2 in the case that the fluid stream contains solid particles that are easily entrained. The arrangements of FIGS. 3A and 3B provide a relatively large volume of substantially stationary fluid in the slurry container 118, surrounding the slurry collection cage. This arrangement provides an increased slurry residence time in the slurry container 118 of FIGS. 3A and 3B, compared with that of FIG. 2. Easily entrained particles are thus allowed a greater time for settling in the slurry container 118, in turn increasing the separation efficiency of the assembly.

[0150] Referring to FIG. 4, there is shown a further embodiment of the separator system of the present invention. The system of FIG. 4 comprises a cap, a separator and a slurry container substantially as described hereinbefore and as shown in FIG. 3 and operates in the same general manner as the system shown in FIG. 3. Accordingly, components common to the systems of both FIGS. 3 and 4 are indicated using the same reference numerals. However, the arrangement shown in FIG. 4 employs an alternative fluid collection regime, the components and operation of which will now be described in more detail.

[0151] The separation system of FIG. 4 employs a light fluid outlet conduit 200 and a heavier fluid outlet conduit 205. The heavier fluid outlet conduit 205 is arranged co-axially within the separation region and extends through the slurry container 118. The heavier fluid outlet conduit 205 extends co-axially at its lower end portion within the slurry collection cage 172, forming an annular chamber for the collection of slurry through the slots.

[0152] The light fluid outlet conduit 200 has a vortex arrestor assembly 201 at the gas liquid level 203 to hinder the formation of a vortex and prevent heavier fluid being drawn into the light fluid outlet conduit 200. The light fluid outlet conduit 200 is provided with a plurality of tangential fluid ports 211 disposed so as to open into the core region above the vortex arrestor 201. As shown in FIG. 4, the interface between the core region and annular region within the separator 104 is indicated by the dotted line 125. It is preferred that the light fluid outlet conduit 200 is of a length such that, in operation, the lower or downstream end of the core region intersects the light fluid outlet conduit 200 at or close to its lowermost end, above the vortex arrestor assembly 201.

[0153] The fluid outlet 130 in the cap 106 connects with a liquid trap 204 mounted to the upper end of the cap 106 by a flange and bolts. The liquid trap 204 comprises a central chamber 206 and a fluid feed pipe 208 extending co-axially upwards within the chamber 206 from the fluid outlet 130 in the cap 106. The fluid feed pipe 208 has its upper end sealed with a domed cap 210 and a plurality of tangential fluid ports 212 opening into the chamber 206. A tangentially arranged fluid outlet 214 is disposed in the upper portion of the wall of the liquid trap 204, which connects the chamber 206 with a fluid line 216. A plurality of drain ports 218 extend from the lower end of the chamber 206 in the liquid trap 204 to corresponding ports 220 formed in the end of the cap 106 opening into the separation region to enable liquid to be recirculated as shown in FIGS. 1A and 1B.

[0154] The heavier fluid outlet conduit 205 is capped at its upper end by a dome cap 209 and is provided in its upper portion with a plurality of tangential fluid ports 213. The heavier fluid outlet conduit 205 connects with a fluid outlet port 222 in the slurry container 118, which in turn is connected to a fluid line 224. The fluid line is shaped to form a weir 225 having a level corresponding to that of the downstream end of the core region, as indicated in FIG. 4.

[0155] A cone 226 extends around the heavier fluid outlet conduit 205 in a region below the tangential fluid ports 213. The cone 226 is provide with an annular passage 228 adjacent the outer surface of the heavier fluid outlet conduit 205, to provide a passage for fluid to pass upwards and out of the slurry container 118 for collection.

[0156] In operation, fluid is removed from the separator in two ways. First, the least dense fluid collected in the core region, most typically gas, passes through the ports 211 in the fluid outlet conduit 200 and flows in an upstream direction through the cap 106 and into the fluid feed pipe 208 in the liquid trap 204. The fluid leaves the fluid feed pipe 208 through the tangential ports 212, imparting a rotational flow pattern to the fluid in the chamber 206. Dense phases, such as liquid and any entrained solid particles, move to the wall of the chamber 106 and flow downwards, returning to the separation region within the cap 106 through the drain ports 218 and 220 and due to the angled tangential inlet flow, is entrapped and removed in the main flow stream, as shown in FIGS. 1A and 1B. The remaining fluid, typically gas, leaves the chamber 206 through the outlet 214 and passes into the fluid line 216. The fluid line 216 is shaped so as to form a gas weir 217.

[0157] Denser fluid leaves the separator downstream of the core region by passing through the ports 213 in the heavier fluid outlet conduit 205, and flows in a downstream direction within the conduit 205 through the slurry cage and into the fluid line 224 via the fluid outlet 222 in the slurry container 118.

[0158] A further embodiment of the present invention is shown in FIG. 5. The system of FIG. 5 comprises a cap, a separator and a slurry cage substantially as described hereinbefore and as shown in FIG. 3 and operates in the same general manner as the system shown in FIG. 3. Accordingly, components common to the systems of both FIGS. 3 and 5 are indicated using the same reference numerals. However, the arrangement shown in FIG. 5 employs a further alternative fluid collection regime, the components and operation of which will now be described in more detail.

[0159] Referring to FIG. 5, a fluid collection assembly 300 extends co-axially within the separation region from the end of the cap 106 to the region of the junction between the separator 104 and the slurry container 118. The fluid collection assembly 300 comprises inner and outer conduits 302 and 304 arranged concentrically so as to form an annular channel 306 between the two. The lower end of the outer conduit 304 is closed. In operation, the lower end of the outer conduit 304 will lie at the gas/liquid level 203. A plurality of fluid ports 310 are provided in the outer conduit 304 and correspond in form, arrangement and function to the ports 211 shown in FIG. 4 and described above.

[0160] The inner conduit 302 extends within the outer conduit 304 and projects from the lower end of the inner conduit 302, such that its lower end is disposed below the core region, when the separator system is in operation. The inner conduit 302 is provided in its lower end portion with fluid ports 213 of the type described and shown in FIG. 4. A vortex arrestor assembly 308 is disposed on the lower end of the inner conduit 302.

[0161] The cap 106 is provided with an annular liquid knockout chamber 312 connected to the annulus 306 in the fluid collection assembly 300. The inner conduit 302 extends through the annular liquid knockout chamber 312 to a first fluid outlet 314 in the end of the cap 106, which in turn connects to a fluid line 316. The cap comprises a second fluid outlet 318 in the wall of the liquid knockout chamber 312, which is connected to a fluid line 320.

[0162] The fluid line 316 extends from the cap 106 to a level below the effective end of the outer conduit 304 of the fluid outlet assembly 300. In this way, the flow of fluid through the fluid line 316 provides a siphon to aid fluid removal from the separator.

[0163] The liquid knockout chamber 312 is connected to the separation region within the cap 106 by means of a plurality of fluid return ports 326.

[0164] In operation, fluid enters the fluid outlet assembly 300 through the ports 310 in the outer conduit 304 from both the core region and the outer annular region of the separator 104. The low density fluid from the core region passes upwards through the annulus 306 into the liquid knockout chamber 312 in the cap 106. In the scenario described hereinbefore, this will consist mostly of gas. Higher density components, such as liquid, are removed from the low density fluid in the liquid knockout chamber 312 and return to the separation region in the cap by way of the return ports 326. The low density fluid leaves the cap through the second fluid outlet 318 and enters the fluid line 320, which is shaped so as to form a gas weir 217.

[0165] Fluid from the annular region of the separator is drawn into the inner conduit 302 and passes upwards through the cap 106 and leaves via the first fluid outlet port 314. In the scenario outlined above, this fluid will consist essentially of liquid, with some entrained gas. The remaining fluid in the fluid line 316 is passed to downstream equipment for further processing.

[0166] It has been found that an assembly according to the present invention as shown in the accompanying figures can separate a combined stream of crude oil, water and solid debris at flowrates up to 25,000 BPD at very high efficiency. In addition, the assembly can operate with a very high turn down ratio, that is a given assembly can operate over a wide range of fluid flowrates. For example, the assemblies shown in the accompanying figures can operate as low as 5,000 BPD to separate a combined crude oil, water and solids stream. Below these flowrates, separation of the components due to fluid rotation diminishes and the assembly will operate under gravity separation principles. Accordingly, separation at flowrates from zero upwards may be achieved.

[0167] Referring to FIG. 6, there is shown a separation assembly according to the present invention incorporating an inlet assembly according to the final aspect of the present invention. Features of FIG. 6 common to other embodiments of the present invention are indicated using the same reference numerals. The inlet assembly, generally indicated as 500, comprises a feed conduit 502 through which a fluid to be separated is fed to the assembly. The inlet assembly 500 further comprises an arcuate conduit 504 through which fluid may be conveyed to feed pipe 124 and the inlet 126.

[0168] As shown in FIG. 6, the arcuate conduit 504 extends in a helical pattern, with the fluid completing two complete turns between the feed conduit 502 and the inlet 126. It will be appreciated that the arcuate conduit 504 may be arranged in a different configuration, for example a helical pattern with greater or fewer turns, as may be required. As shown in FIG. 6, the arcuate conduit 504 is a helical pipe. It will be appreciated that an arcuate flowpath for the fluid may be obtained by providing an arcuate conduit of a different configuration.

[0169] In operation, a fluid stream to be separated in the separation assembly first flows along the arcuate conduit 504, within which the components of the fluid stream begin to separate according to their relative densities. Thus, the heavier components, for example liquids, such as water, and solids, will tend towards the radially outer regions of the conduit. In contrast, the lighter components, such as light liquids, for example oil, and gases, will tend to the radially inner portion of the conduit. The conduit 504 and the inlet 126 are arranged such that fluid stream is properly oriented with the flow patterns prevailing within the separation region. Thus, the heavier components enter the separator 104 in a radially outer position and the lighter components enter the separator 104 in a radially inner position. It will thus be appreciated that the separation initialised within the arcuate conduit 504 supplements the separation taking place within the separator 104.

[0170] Referring to FIGS. 7 and 8, there is shown a separator according to a further embodiment of the present invention. The separator has the same general configuration as that of FIG. 4 and the components common to the embodiment of FIGS. 7 and 8 and FIG. 4 are identified using the same reference numerals. Reference to the foregoing detailed description is made with respect to these common features and components. The following description relates to the features particular to the separator of FIGS. 7 and 8. For clarity, FIGS. 7 and 8 show only the internal components of the separation system, with the external components, such as the inlet assembly, and fluid and solid outlet assemblies being omitted.

[0171] The separation assembly of FIG. 7 has a tangential inlet assembly 602, as hereinbefore described, through which a fluid stream is introduced into the upstream region of the separation region. The inlet assembly 602 has an inlet opening 604 that opens into the separation region some distance from the upstream end of the separation region. A wall assembly 606 is provided having a helically extending guide surface 608 disposed such that incoming fluid contacts the guide surface 608 and is caused to flow in a helical pattern downwards within the separation region. The inlet region is shown in more detail in FIG. 8, with the wall assembly 606 and the guide surface 608 being shown in greater detail. The presence of the wall assembly 606 allows the inlet assembly 602 to be angled more closely to the perpendicular to the longitudinal axis of the separation region, while still allowing the incoming fluid stream to develop the required helical flow pattern within the separation region. Thus, the angle a of the inlet conduit as shown in FIG. 8 is approximately 5o. A further effect of the wall assembly and the use of the guide surface 608 is to ensure that the incoming fluid is not caused to contact and impact the fluid already rotating within the separation region. This in turn reduces the shear to which the fluid is subjected, improving the separation efficiency of the system.

[0172] The separator of FIG. 7 further comprises a slurry container 618 and slurry collection assembly, generally as hereinbefore described, in particular as shown in FIG. 3B. The separator comprises a slurry cage 620. To provide a constriction in the downward fluid flowpath, the slurry collection cage 620 has its upper end closed by a conical cap 622. A vent port 624 extends vertically through the conical cap 622. The vent port 624 in the conical cap 624 provides an outlet for fluid displaced from the slurry container 618.

[0173] In the slurry container 618, fluid and solid particles are caused to try and concentrate on the separator axis and to flow through the tangential slots 630 and enter the slurry collection cage 620, from where they are discharged through the slurry outlet 632. Debris and very coarse solids in a fluid slurry do not enter the slurry cage 620 and are removed from the slurry container through the debris outlet 634. The slurry collection cage 620 of the separator assembly of FIG. 7 is extended in length, compared with that shown in FIG. 3B. To reduce the rotation of the fluid stream in the slurry container 618 and enhance the separation of solids and fluids, the slurry cage 620 is provided with a plurality of baffles 640 extending radially outwards across the slurry container. The baffles 640 are of such a size, number and pitch as to ensure that the fluid stream is sufficiently slowed but still moving enough to provide for easy purging of the solid slurry through the debris outlet 634.

[0174] To enhance the separation of solids from the fluid phases, the inner wall of the slurry container 618 is provided with a conical portion 650 adjacent the debris outlet 634, in order to reduce the cross-sectional area of the slurry container in the downstream direction.

[0175] Referring to FIG. 9, there is shown a subsea processing assembly 900 comprising a wellhead assembly 902 through which fluids are produced from a subterranean well. The subsea processing assembly 900 also includes a separator assembly 904 having a fluid inlet connected to the wellhead assembly for receiving the fluids produced from the well, the separator assembly being operable at wellhead pressure to remove well debris entrained in the fluids to produce a solids-rich phase and a fluid phase, the separator assembly 904 comprising a fluid outlet for the fluid phase. The subsea processing assembly also comprises a choke assembly 906 (similar to the choke 132 discussed above) having an inlet connected to the fluid outlet of the separator assembly 904.

[0176] Referring to FIG. 10, the separation assembly of the present invention may be employed on an offshore platform 1000 receiving production fluids directly from either platform wellheads or a subsea wellhead 1002 through a riser 1004 or the like upstream of the choke (similar to the choke 132 discussed above). Accordingly, in a further aspect, the present invention provides a platform processing assembly 1006 comprising a fluid receiving assembly 1008 for receiving fluids produced from a subterranean well. The platform processing assembly 1006 further comprises a separator assembly 1010 having a fluid inlet connected to the fluid receiving assembly 1008 for receiving the fluids produced from the well, the separator assembly 1010 being operable at wellhead pressure to remove well debris entrained in the fluids to produce a solids rich phase and a fluid phase, the separator assembly 1010 comprising a fluid outlet for the fluid phase. The platform processing assembly 1006 further comprises a choke assembly 1012 having an inlet connected to the fluid outlet of the separator assembly 1010.