WO2011059919A1

WO2011059919A1 - Subsea separation systems

Info

Publication number: WO2011059919A1
Application number: PCT/US2010/055835
Authority: WO
Inventors: Karl Gregory Anderson; Sr. Raul Jasso Garcia; Alan Dale Leitko; Sandeep Patni; Moye Wicks Iii
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2009-11-12
Filing date: 2010-11-08
Publication date: 2011-05-19

Abstract

A separation system for a multiphase fluid containing a high density component and a low density component comprising a separator; an inlet for the multiphase fluid to enter a top portion of the separator; a plurality of fins within the separator defining a plurality of annular flow paths within the separator; an outlet for the high density component at a bottom portion of the separator below the fins; and an outlet for the low density at a top portion of the separator above the fins.

Description

SUBSEA SEPARATION SYSTEMS

Field of the Invention

The present invention is directed to subsea separation systems.

Background of the Invention

U.S. Patent Number 6,036,749 discloses a liquid/gas helical separator that operates on a combination of centrifugal and gravitational forces. The separator includes a primary separator formed basically by an expansion chamber, a secondary separator formed basically by a helix for directing the flow, a tertiary separator which consists of a reservoir or gravitational-separation tank and of a transition region between the primary and secondary separators, which consists of at least two variable-pitch helixes whose inclination varies from an angle of 90 DEG to the angle of inclination of the constant-pitch helix of the secondary separator with the function of providing a gentler flow of the liquid phase at the transition between the first two separators. U.S. Patent Number 6,036,749 is herein incorporated by reference in its entirety.

U.S. Patent Number 7,540,902 discloses a slug flow separator that facilitates the separation of a mixture flow into component parts. The separator includes an upper-tier elongate conduit, a lower-tier elongate conduit and a plurality of spaced apart connectors. Each of the upper and lower-tier elongate conduits has an outlet and at least one of the upper and lower-tier elongate conduits has an inlet for receiving the mixture flow. The upper and lower-tier elongate conduits also each have a plurality of openings such that one connector of the plurality of connectors may interconnect one of the upper-tier elongate conduit openings with a one of the lower-tier elongate conduit openings. The connectors enable communication of at least one of a liquid component and the at least one of another liquid component and a gas component of the mixture flow there between. U.S. Patent Number 7,540,902 is herein incorporated by reference in its entirety.

U.S. Publication Number 2009/021 1763 discloses a Vertical Annular Separation and Pumping System (VASPS) utilizing an isolation baffle to replace a standard pump shroud associated with an electrical submersible pump. The isolation baffle may be a one piece plate positioned so as to direct produced wellbore liquids around the electrical submersible pump motor to provide a cooling medium to prevent overheating and early failure of the electrical submersible pump. U.S. Publication Number 2009/021 1763 is herein incorporated by reference in its entirety.

U.S. Publication Number 2009/0035067 discloses a seafloor pump assembly that is installed within a caisson that has an upper end for receiving a flow of fluid containing gas and liquid. The pump assembly is enclosed within a shroud that has an upper end that seals around the pump assembly and a lower end that is below the motor and is open. An eduction tube has an upper end above the shroud within the upper portion of the caisson and a lower end in fluid communication with an interior portion of the shroud. The eduction tube causes gas that separates from the liquid and collects in the upper portion of the caisson to be drawn into the pump and mixed with the liquid as the liquid is being pumped. U.S. Publication Number 2009/0035067 is herein incorporated by reference in its entirety.

International Publication Number WO 2007/144631 discloses a method of separating a multiphase fluid, the fluid comprising a relatively- high density component and a relatively low density component, comprises 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; wherein 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 disclosed. 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. International Publication Number WO 2007/144631 is herein incorporated by reference in its entirety. International Publication Number WO 2009/047521 discloses equipment and a subsea pumping system using a subsea module installed on the sea bed, preferably away from a production well and intended to pump hydrocarbons having a high associated gas fraction produced by one or more subsea production wells to the surface. A pumping module (PM) is disclosed which is linked to pumping equipment already present in a production well and which basically comprises: an inlet pipe, separator equipment, a first pump and a second pump. In the subsea pumping system for the production of hydrocarbons with a high gas fraction, when oil is pumped from the production well (P) the well pump increases the energy of the fluid in the form of pressure and transmits this increase in energy in the form of an increase in suction pressure in the second pump of the subsea module (PM). International Publication Number WO 2009/047521 is herein incorporated by reference in its entirety.

Co-pending U.S. patent application 61 /255,212, filed October 27, 2009, having attorney docket number TH3898 discloses a method for separating a multiphase fluid, the fluid comprising a relatively high density component and a relatively low density component, the method comprising: introducing the fluid into a separation region; imparting a rotational movement into the multiphase fluid; forming an outer annular region of rotating fluid within the separation region; and forming and maintaining a core of fluid in an inner region; wherein 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. U.S. patent application 61 /255,21 2 is herein incorporated by reference in its entirety.

There is a need in the art for one or more of the following:

An improved system and method of separating gases and liquids in a subsea environment;

An improved system and method of reducing the gas input to a submersible pumping system; An improved system and method of increasing the throughput of a subsea caisson separator; and

An improved system and method to extend the pump life and reduce maintenance downtime of a submersible liquid pump.

Summary of Invention

In one aspect of the invention, there is disclosed a separation system for a multiphase fluid containing a high density component and a low density component comprising a separator; an inlet for the multiphase fluid to enter a top portion of the separator; a plurality of fins within the separator defining a plurality of annular flow paths within the separator; an outlet for the high density component at a bottom portion of the separator below the fins; and an outlet for the low density at a top portion of the separator above the fins

Advantages of the invention may include one or more of the following:

An improved system and method of reducing the gas input to a submersible pumping system;

An improved system and method of increasing the throughput of a subsea caisson separator; and

Brief Description of Drawings

Figure 1 shows an offshore production structure.

Figure 2 shows a gas and liquid separator.

Figures 3a and 3b show a gas and liquid separator in accordance with embodiments of the present disclosure. Figure 4 shows a gas and liquid separator in accordance with embodiments of the present disclosure.

Detailed Description of the Invention

In one aspect, embodiments of the present disclosure generally relate to a offshore platform for producing oil and/or gas from one or more subsea wells with a subsea pump, for example a spar platform, a tension leg platform, an FPSO, or other offshore structures as are known in the art. In particular, embodiments of the present disclosure relate to one or more subsea wells that are connected to a separator with a gas output and a liquid output, where the liquid output is fed to a subsea pump to transport the liquid to an offshore platform. The offshore platform of the present disclosure may be intended to be deployed across a range of water depths, extending from 300 meters to 3000 meters or more.

Figure 1 :

Referring to Figure 1 , offshore system 100 is shown. System 100 is installed in a body of water, where system 100 includes a floating structure 102 connected to the sea floor by multiple mooring or anchor lines 1 12. Floating structure 102 may include a drilling rig 1 10 to drill wells in the sea floor, and/or other drilling and/or production equipment as is known in the art.

One or more wells 108 are provided in the sea floor to produce liquids and/or gases. Wells 108 are capped with a wellhead 106. Wellhead 106 is connected to a flowline 107 to transport the liquids and/or gases to separation and pumping system 120. Alternatively, the liquids and/or gases from one or more wells 108 may be aggregated at a manifold, then transported by a flowline to pumping system 120.

Although only one pumping system 120 is shown, multiple pumping systems may be provided to increase the capacity and/or provide redundancy during pump downtimes. In one example, from about 2 to about 10 pumping systems may be provided, such as from 3 to 5 pumping systems. Although only flowline 107 from one well 108 is shown, multiple flowlines from multiple wells and/or manifolds may be used to transport liquids and/or gases to pumping system 120.

Pumping system 120 includes a mixed liquid and gas inlet 121 into caisson separator 122. Liquid pump 1 24 is provided at the bottom of caisson separator 122 below liquid level 125. Liquid flowline 126 is connected to pump outlet 124, and gas flowline 1 28 is connected to caisson separator 122 above liquid level 125. Liquid flowline 126 and gas flowline 128 transport liquid and gas, respectively, to floating structure 102. Produced fluids from well 108 may be transported to floating structure 102 for production processes as are known in the art prior to being shipped, pipelined, or otherwise transported to shore.

In general, floating structure 102 is permanently moored on location and is not moved until the field has been exhausted. Floating structure 102 may have a weight of at least 20,000 metric tons.

In one embodiment, caisson separator 122 may be installed at a water depth of at least 1000 meters, for example from about 1500 to about 4000 meters.

In one embodiment, caisson separator 122 may have a length of at least about 30 meters, for example from about 50 to about 200 meters.

In one embodiment, caisson separator 122 may be substantially buried in the sea floor, for example from about 70% to about 99% of the length of the caisson buried in the sea floor, such as from about 80% to about 95% buried.

In one embodiment, caisson separator 122 may have a diameter of at least about 50 centimeters, for example from about 75 to about 200 centimeters, or from about 100 to about 150 centimeters.

Figure 2:

Referring to Figure 2, a separation system 200 is shown in accordance with embodiments of the present disclosure. A mixed liquid and gas inlet 206 is provided at the top of separator 200. Mixed liquid and gas inlet 206 may be inclined at an angle from about 5 to about 60 degrees with respect to horizontal, for example from about 10 to about 45 degrees, or from about 15 to about 30 degrees. In one embodiment, mixed liquid and gas inlet 206 may be directed tangentially to an interior wall of separator 200 to provide a swirling liquid film 220 flowing down the interior wall of separator 200. Gas may separate out of liquid film 220 to gas space 202.

Liquid in the liquid film 220 will gravity drain down towards pump 236 which has a pump outlet connected to a liquid outlet conduit 210. Liquid film 220 may have waves that travel down the interior wall of separator 200. Liquid film 220 may have a thickness from about 0.5 to about 5 centimeters, for example from about 1 to about 3 centimeters. Waves may have a height from about 2 to about 10 centimeters, for example from about 3 to about 6 centimeters.

As liquid film 220 travels down the interior wall of separator 200 it encounters one or more reduced diameter pipe sections that define annular liquid flowpaths 204a, 204b, 204c, and 204d. Annular liquid flowpath 204a is between the interior wall of separator 200 and the first reduced diameter pipe section, while annular liquid flowpaths 204b, 204c, and 204d are between adjacent reduced diameter pipe sections. Each reduced diameter pipe section has a smaller diameter than the pipe section to its exterior to define an annular space between them. The annular spaces have a thickness t 228. Thickness t 228 may be from about 0.25 to about 5 centimeters, or from about 0.5 to about 3 centimeters, or from about 1 to about 2 centimeters.

Separator may have a height H 230 from about 25 meters to about 125 meters, or from about 50 to about 100 meters.

Reduced diameter pipe sections may have a height H 232 from about 5 meters to about 50 meters, or from about 10 meters to about 25 meters. Reduced diameter pipe sections may have a height H 232 from about 5% to about 50% of separator height H 230, for example from about 10% to about 35%, or from about 15% to about 25%. Separator may have a diameter D 226 from about 0.5 meters to about 5 meters, or from about 0.75 to about 3 meters, or from about 1 to about 2 meters.

Gas in the gas space 202 will float up towards gas outlet conduit 208.

Another suitable separator system is disclosed in U.S. Patent 7,540,902 which is herein incorporated by reference in its entirety.

Figures 3a & 3b:

Referring to Figures 3a and 3b, separator system 300 is illustrated including housing 301 , for example a caisson or a cylindrical structure or a long structure with a circular, square, triangular, or other polygonal cross section. Within housing 301 are provided two or more fins 330.

Figure 3b shows a cross section of Figure 3a taken along the line A-A. In the interior is fin 330d, exterior to fin 330d is fin 330c, exterior to fin 330c is fin 330b, exterior to fin 330b is fin 330a, exterior to fin 330a is housing 301 . Although four fins are illustrated more or less fins may be provided, for example from about 1 to about 10 fins, or from about 2 to about 5 fins.

A plurality of annular flow channels are defined between the housing and fin 330a, and between the adjacent fins.

In operation, a mixed flow of liquid and gas, or of a heavy and of a light fluid, is introduced from top manifold 320 by flow inlet 321 . The caisson inlet functions as a primary gravity separator, which may or may not utilize centrifugal separation. The liquid and entrained gas falls down an interior wall of housing 301 . At the top of fins 330, the mixed flow starts traveling down annular flow channels, with the gas (and/or foam) floating to the top, and the liquid dropping to the bottom.

At the bottom of the fins 330, a substantial portion of the gas has floated to the top of separator 300, so that a primarily liquid portion remains in the liquid storage area 304, which goes into pump 324 inlet, for example at least about 80%, 90%, or 95% liquid by volume. Pump 324 has an outlet 326 for pumping the liquid to a desired location, for example a floating production structure. At the top of the separator above the liquid storage area 304, substantially all of the liquid has dropped into the liquid storage area 304 through one of the annular flow channels, so that a primarily gas portion remains in the top of the separator, which goes through an opening of gas outlet conduit 328, located above the fins 330.

In another embodiment, mixed flow conduit 321 may be arranged to provide a tangential flow path so that liquid in the mixed flow is pushed against the housing 301 interior wall by centrifugal acceleration, and the gas is maintained closer to the interior of the flow path 304 near outlet 326.

Figure 4:

Referring to Figure 4, a separation system 400 is shown in accordance with embodiments of the present disclosure. A mixed liquid and gas inlet 406 is provided at the top of separator 400. Mixed liquid and gas inlet 406 may be inclined at an angle from about 5 to about 60 degrees with respect to horizontal, for example from about 10 to about 45 degrees, or from about 15 to about 30 degrees. In one embodiment, mixed liquid and gas inlet 406 may be directed tangentially to an interior wall of separator 400 to provide a swirling liquid film 420 flowing down the interior wall of separator 400. Gas may separate out of liquid film 420 to gas space 402.

Liquid in the liquid film 420 will gravity drain down towards pump 436 which has a pump outlet connected to a liquid outlet conduit 410. Liquid film 420 may have waves that travel down the interior wall of separator 400. Liquid film 420 may have a thickness from about 0.5 to about 5 centimeters, for example from about 1 to about 3 centimeters. Waves may have a height from about 2 to about 10 centimeters, for example from about 3 to about 6 centimeters.

As liquid film 420 travels down the interior wall of separator 400 it encounters one or more reduced diameter pipe sections that define annular liquid flowpaths 404a, 404b, 404c, and 404d. Annular liquid flowpath 404a is between the interior wall of separator 400 and the first reduced diameter pipe section, while annular liquid flowpaths 404b, 404c, and 404d are between adjacent reduced diameter pipe sections. Each reduced diameter pipe section has a smaller diameter than the pipe section to its exterior to define an annular space between them. The annular spaces have a thickness t 428. Thickness t 428 may be from about 0.25 to about 5 centimeters, or from about 0.5 to about 3 centimeters, or from about 1 to about 2 centimeters.

Separator may have a diameter D 426 from about 0.5 meters to about 5 meters, or from about 0.75 to about 3 meters, or from about 1 to about 2 meters.

Gas in the gas space 402 will float up towards gas outlet conduit 408.

In the embodiment shown in Figure 4, the reduced diameter pipe sections may have different heights, and may have the tops of the pipe sections aligned at the same location in the separator, while the bottoms of the pipe sections are at different locations in the separator. In another embodiment shown in Figure 2, the reduced diameter pipe sections may have different heights, and may have the tops of the pipe sections at different locations in the separator, while the bottoms of the pipe sections are aligned at the same location in the separator. In other embodiments (not shown), the reduced diameter pipe sections may have the same or similar heights, and may have the tops and bottoms of the pipe sections aligned at the same location in the separator. In other embodiments (not shown), the reduced diameter pipe sections may have different heights, and may have the tops and bottoms of the pipe sections at different locations in the separator.

Illustrative Embodiments:

In one embodiment, there is disclosed a separation system for a multiphase fluid containing a high density component and a low density component comprising a separator; an inlet for the multiphase fluid to enter a top portion of the separator; a plurality of fins within the separator defining a plurality of annular flow paths within the separator; an outlet for the high density component at a bottom portion of the separator below the fins; and an outlet for the low density at a top portion of the separator above the fins While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

C L A I M S

1 . A method for separating a multiphase fluid, the fluid comprising a relatively high density component and a relatively low density component, the method comprising: introducing the fluid into a separator; flowing the fluid down an interior wall of the separator; separating the fluid into a plurality of annular flow paths separated by one or more fins interior to the interior wall of the separator; recovering the relatively low density component from a top portion of the separator above the fins; and recovering the relatively high density component from a bottom portion of the separator below the fins.

2. The method according to claim 1 , wherein the multiphase fluid comprises a liquid phase and a gaseous phase.

3. The method according to one or more of claims 1 -2, wherein the multiphase fluid is produced from a subterranean oil well.

4. The method according to one or more of claims 1 -3, wherein the multiphase fluid is introduced tangentially against the interior wall of the separator, thereby causing the fluid in the separator to rotate.

5. The method according to one or more of claims 1 -4, wherein the high density component is removed by pumping.

6. A separation system for a multiphase fluid containing a high density component and a low density component comprising: a separator; an inlet for the multiphase fluid to enter a top portion of the separator; a plurality of fins within the separator defining a plurality of annular flow paths within the separator; an outlet for the high density component at a bottom portion of the separator below the fins; and an outlet for the low density at a top portion of the separator above the fins.