WO2007055591A1 - Unit for gas treatment in rotating equipment for subsea compression - Google Patents

Unit for gas treatment in rotating equipment for subsea compression Download PDF

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Publication number
WO2007055591A1
WO2007055591A1 PCT/NO2006/000409 NO2006000409W WO2007055591A1 WO 2007055591 A1 WO2007055591 A1 WO 2007055591A1 NO 2006000409 W NO2006000409 W NO 2006000409W WO 2007055591 A1 WO2007055591 A1 WO 2007055591A1
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WO
WIPO (PCT)
Prior art keywords
gas
compressor
conditioning unit
subsea
motor
Prior art date
Application number
PCT/NO2006/000409
Other languages
French (fr)
Inventor
Ola SKRØVSETH
Asbjørn ERIKSEN
Bernt Bjerkreim
Karl Olav Haram
Original Assignee
Norsk Hydro Produksjon A.S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Norsk Hydro Produksjon A.S filed Critical Norsk Hydro Produksjon A.S
Publication of WO2007055591A1 publication Critical patent/WO2007055591A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D29/00—Details, component parts, or accessories
    • F04D29/70—Suction grids; Strainers; Dust separation; Cleaning
    • F04D29/701—Suction grids; Strainers; Dust separation; Cleaning especially adapted for elastic fluid pumps
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/01—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells specially adapted for obtaining from underwater installations
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D25/00—Pumping installations or systems
    • F04D25/02—Units comprising pumps and their driving means
    • F04D25/06—Units comprising pumps and their driving means the pump being electrically driven
    • F04D25/0686—Units comprising pumps and their driving means the pump being electrically driven specially adapted for submerged use
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
    • F04D31/00—Pumping liquids and elastic fluids at the same time

Definitions

  • the present invention relates to a subsea system for well fluid boosting by compressing hydrocarbon gases and pumping hydrocarbon liquids. More particularly, the invention relates to a gas conditioning unit or assembly for conditioning a well stream from a well for the production of a hydrocarbon gas to make it suitable for pressurization purposes in said system.
  • the system is particularly developed for deep sea compression stations.
  • An offshore gas field may be developed with seabed installations which are tied back to terminals onshore or to an offshore platform.
  • the seabed installation comprises one or more production templates where each template produces well fluids through manifold headers that are connected to one or more pipelines.
  • the pipelines transport well fluids to an onshore terminal, an offshore platform or any other receiving facility for further processing.
  • Processed gas and condensate are exported to the market.
  • One or more umbilicals for power, control and utility supplies are installed from the receiving facility to the subsea installation.
  • well fluids may flow into the receiving facility by means of the reservoir pressure. Later in the productions phase or at start-up of the production, well fluid boosting is required in order to maintain the production level and to recover the anticipated gas and condensate volumes. This is may be performed by a subsea compressor assembly.
  • Subsea compressors for this purpose with electric motors that requires a dry environment, and that utilizes a pressurised, gas filled motor housing are for instance disclosed in Norwegian Patents Nos. NO 172075, NO 173197, Norwegian Patent Application No. 2001 5199 as well as Norwegian Patent Application No. 2003 3034.
  • Norwegian Patent Application 2003 3034 discloses a gas compressor module with a pressure housing.
  • the module includes an electric motor and a compressor connected with at least one shaft.
  • the shaft is carried by magnetic bearings.
  • the application describes volume and pressure control of the gas flowing into the motor, and the use of a supply of dry hydrocarbon gas. Furthermore means for sensing the pressure in the inlet and outlet is described, whereby based on the measured pressure, the pressure and volume regulator controls the pressure for injection of gas from the supply into the motor housing.
  • the application does however not solve the problem with how to handle mercury in the gas flow, and how to provide a sufficiently dry gas for the use as a pressure medium in the compressor station components.
  • the system according to the present invention defining a gas conditioning unit for conditioning a well stream.
  • the well stream includes a hydrocarbon gas, and this gas is conditioned to a substantially dry gas for use in subsea components.
  • the gas must be processed or conditioned to remove solid particles and liquids suspended in the gas, as the gas is to be used in components requiring a controlled environment in a pressure housing. Gas is frequently introduced in pressure housings for components to provide cooling of the components, to avoid corrosion, to prevent of unfavourable external influence by ingress of water etc.
  • the gas conditioning unit includes a hydro cyclone separator and a water separation filter.
  • the gas conditioning unit may further include a screen unit with a silver surface for the gas to pass through to act as an anode for mercury content in the gas.
  • a screen unit with a silver surface for the gas to pass through to act as an anode for mercury content in the gas.
  • Many components, in particular components used in connection with electricity are made of copper, and when copper is used mercury should be avoided. Furthermore, accumulation of mercury may cause short circuits in electric components.
  • the gas conditioning unit may further included an inlet in fluid connection with the outlet of the compressor and a liquid outlet in connection with a liquid side of an inlet liquid separator.
  • a gas outlet in of the compressor may be in connection with a gas side of an inlet liquid separator of the compressor, performing the main separation of the gas and the liquid components of the well flow before the gas enters the compressor to avoid two phase compression.
  • the water separation filter may be a coalescing filter.
  • a subsea compression module may include an electric motor and a compressor with an inlet and an outlet, driven by the motor for pressurising at least a part of the well stream.
  • a conditioning unit includes a hydro cyclone separator and a water separation filter for conditioning the pressurised well stream to a substantially dry clean gas. The gas is intended for compressing subsea components in a pressure chamber requiring a controlled environment.
  • the subsea components may include the motor driving the compressor.
  • the subsea components may include a motor driving a pump for the liquid phase of the well stream.
  • the subsea components may include the motor driving the compressor, the compression module may be a natural gas well flow pressure boosting station, and the conditioning unit may be adapted to only condition a fraction of the total compressed well flow.
  • the compressor may be a multistage compressor, and the gas to the conditioning unit may be is taken from an intermediate stage of the compressor.
  • Joule Thomson valves has been used for liquid separation in gas conditioning units.
  • gas might contain fines and sand it is foreseen that the valve will be exposed to heavy erosion.
  • cyclone separators is introduced to separate the remaining particles, which have not been separated out in an inlet scrubber prior to entering the system.
  • the pressure loss over the cyclone separator is as low as possible.
  • the higher density fluid and fines separates from the gas and goes to the bottom before being routed back in to the inlet scrubber.
  • the gas with the less density will exit the cyclone separator on the top, entering into the water separation filter for the final cleaning prior entering into the components of the system such as the motor, accumulator or being routed back into the scrubber.
  • gas conditioning unit according to the invention may be separately retrievable.
  • the gas-conditioning unit may further include a vessel unit with a silver surface and or silver mesh for the gas to pass through which will act as a sacrificial anode for the mercury content in the gas.
  • the dimensioning of the gas exposed silver surface will be dependant of the mercury content in the gas being feed through the gas conditioning unit.
  • the introduction of the silver mesh is to reduce the impact of the mercury in particular on copper components such as windings and connections in a motor.
  • the gas conditioning unit may include an inlet in fluid connection with the outlet of the compressor, and a liquid outlet in connection with a liquid side of an inlet liquid separator.
  • a pump may have to be used to pump liquid from the conditioning unit into the liquid separator.
  • a gas outlet may be connected to a gas side of the inlet liquid separator.
  • the system may be used in conjunction with a separate coupling chamber separated from the compressor and the motor by seals, which includes a separate specifically controlled pressure. This pressure is controlled to be higher than the pressure in the motor chamber and lower than the suction pressure of the compressor.
  • a subsea compression station where this system may be included may comprise the following modules and parts: one or more compressor trains, one or more circuit breaker modules, inlet and outlet manifolds, inlet coolers (if supply pipelines not are sufficient for cooling the well stream), inlet sand trap (for accidental sand production), parking location for main transformer and power umbilical termination head, prosess system, control system.
  • the compressor train may include: compressor module, compressor variable speed drive (VSD), anti surge valve and actuator, anti surge cooler, separator/scrubber module, pump module, pump VSD (variable speed drive), remote and manually operated valves, interconnection piping, control system including control modules.
  • the compressor may be driven directly by high-speed motor.
  • the electric motor may be cooled with a hydrocarbon gas at a pressure controlled to be equal or close to the suction pressure of the compressor.
  • the gas source is the well stream supplied to the subsea compression station, and the gas must be conditioned prior to entering the electric motor.
  • the material properties of the compressor unit should be suitable for operation with relevant contents of H 2 S and CO 2 .
  • the compressor and the material properties should be designed for the liquid fractions and solids content coming with the gas stream from an upstream separator.
  • the size and distribution of liquid droplets and solids particles are dependent on the separator design, and the separator should be designed to bring the content of liquids and solids down to an acceptable level.
  • the compression system may be designed to handle the continuous fines/sand production.
  • the rotating equipment may be protected against wear and degradation from solids to ensure high efficiency, long life and reliability.
  • the compressor may include an anti-surge control recycle line designed for full recycle flow at maximum conditions speed (105%).
  • the anti-surge control valve may be an electrically actuated, axial stroke design and may be located close to the compressor discharge at high point.
  • An anti-surge recycle cooler may be included downstream of the anti-surge valve in the recycling pipe loop.
  • the compressors may have a discharge pipe equipped with a remote operated isolating valve.
  • a non-return valve may be fitted in the compressor discharge pipe upstream of the isolation valve.
  • the separator separates liquid/solids from the gas, which in turn is ingested into the pump and compressor, respectively.
  • the separator is designed to separate liquids and solids from the gas flow to avoid excessive erosion of the compressor, and to ensure clean dry gas to the various chambers, including the motor chamber and the compressor chamber.
  • the separator is designed to ensure that solids not are clogged or undesirably accumulated anywhere in the separator.
  • the compression station may include various process coolers such as an anti surge cooler/recycle cooler to cool the gas flow in the anti surge line (compressor recycle loop) and input coolers to cool the flow from templates.
  • process coolers such as an anti surge cooler/recycle cooler to cool the gas flow in the anti surge line (compressor recycle loop) and input coolers to cool the flow from templates.
  • the compressor station may have tie-in connections for well fluid discharge, and may include ROV or remotely operated valves for routing of the well fluid to the different pipelines.
  • the well fluid from tied-in production templates may be distributed to a separator equipped with a remotely actuated isolation valve in the inlet pipe, this being either a hydraulicaily or electrically actuated valve.
  • the well stream may further be routed via the compressor by-pass line before compressor start up and the by-pass valve may be closed when the compressors are brought into operation.
  • Most of the solids from the production may be removed in separators. Sand/fines/solids entering the compression station will be separated out in the separator and transported via the liquid pump to the discharge pipeline.
  • a sand trap for accidental sand production may be used to remove sand from the inlet well fluid. Gas demisting and gas-liquid separation may be performed by the use of scrubbers.
  • Fig. 1 is a schematic representation of a subsea compression module with a gas conditioning unit according to an embodiment of the invention.
  • Fig. 1 shows a subsea compressor module according to an embodiment of the invention.
  • the module includes an electric motor 1 , a coupling chamber 2 or intermediate chamber and a compressor 3.
  • the motor 1 is connected to the compressor 3 with a coupling K in the coupling chamber 2.
  • motor 1 and the compressor 3 may be connected to the same shaft.
  • the coupling K may for instance be a flange or any other suitable joint.
  • the coupling chamber 2 may include a transmission if a certain ratio is needed between the motor 1 and the compressor 3.
  • a seal T1 is provided on the output shaft of the motor, where the shaft enters the coupling chamber.
  • a seal T2 is provided on the input shaft of the compressor where this shaft enters the coupling chamber.
  • An inlet liquid separator 5 receives a well flow and delivers a substantially dry gas to the compressor at a pressure P1.
  • a line L3 from the separator 5 controls the differential pressure between the liquid separator 5 and the supply line from the gas conditioning unit Pr ensuring that the motor pressure Pm is maintained at a higher level than P1.
  • a line L4 connects the coupling chamber 2 and the liquid separator 5.
  • a valve V1 ensures that the pressure Pk in the coupling chamber 2 is less than the pressure Pm in the motor chamber.
  • a line L1 from the well and into the compressor 3 is at a suction pressure P1.
  • the compressor delivers a compressed outlet fluid flow through line L2.
  • the motor and the compressor are connected with a shaft and a coupling K placed inside the coupling chamber 2.
  • the pressure housing for motor 1 includes electric connections and lines for supply of clean/conditioned gas.
  • the coupling chamber 2 receives gas leaking from the compressor 3 through seal T2. From the motor side, the coupling chamber 2 can receive gas that leaks through seal T1 from the motor as the pressure in the motor Pm is above the pressure in the coupling chamber Pk and above the suction pressure P1 of the compressor.
  • the coupling chamber 2 includes connections for an outlet L4 for fluids leaking from the motor chamber 1 and the compressor chamber 2.
  • a pressure sensor or probe is placed in the inlet liquid separator 5 and in the coupling chamber Pk for monitoring the respective pressures and a further pressure controller Pr controls the pressure of the gas in the motor chamber 1 from the conditioning unit 6. This ensures that the pressure in the motor chamber Pm is maintained at a higher level than the suction pressure P1 of the compressor and the pressure Pk in the coupling chamber. Leaking gas with a pressure P3 is returned to the suction side or the liquid separator to prevent collection of impure gas in the sealing system for the motor.
  • the seals T1 and T2 may be of various types, and may for instance be brush seals or labyrinth seals, both types being well known within the field.
  • the liquid separator 5 ensures a single phase flow to the compressor. Water separation filters may also be included.
  • the motor chamber is supplied with a conditioned gas from the main process conditioning unit 6.
  • the conditioning unit 6 ensures that that the gas entering the motor chamber not is more polluted than the inner components can tolerate.
  • the conditioning unit 6 utilizes a hydro cyclone and a water separation filter.
  • the unit may also include a screen, grid or mesh covered with, or made of, silver for the gas to pass through to form an anode for mercury. Any structure allowing contact between the gas and the metal may be used.
  • the conditioning unit may receive fluid at high or intermediate pressure from the compressor.
  • the pressure sensor placed in the inlet liquid separator 5 and in the coupling chamber 2 registers the respective pressures and ensures that the pressure Pm in the motor chamber is above the pressure in the coupling chamber.
  • the pressure regulator Pr controls the pressure of the gas inn to the motor chamber from the conditioning unit 6 at a pressure P4. This ensures that the pressure Pm in the motor chamber is above the inlet or suction pressure P1 of the compressor and the pressure Pk in the coupling chamber.
  • Gas taken at a pressure P4 from the conditioning unit 6 is led to the pressure regulator Pr through line L5 for further delivery of gas to the motor at pressure Pm.
  • Gas from the conditioning unit 6 may be supplied to the liquid separator 5.
  • the pressure regulator Pr is also connected to the liquid separator through Line L3. Conditioned gas not utilised by the motor is routed back into the liquid separator 5.

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  • General Engineering & Computer Science (AREA)
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Abstract

The present invention concerns a gas conditioning unit 6 for conditioning a well stream. The unit conditions a hydrocarbon gas to a substantially dry gas for use in subsea components requiring a controlled environment. The gas conditioning unit includes a hydro cyclone separator and a water separation filter. Furthermore the invention relates to a subsea compression module with a conditioning unit.

Description

"Unit for gas treatment in rotating equipment for subsea compression"
The present invention relates to a subsea system for well fluid boosting by compressing hydrocarbon gases and pumping hydrocarbon liquids. More particularly, the invention relates to a gas conditioning unit or assembly for conditioning a well stream from a well for the production of a hydrocarbon gas to make it suitable for pressurization purposes in said system.
The system is particularly developed for deep sea compression stations.
An offshore gas field may be developed with seabed installations which are tied back to terminals onshore or to an offshore platform. The seabed installation comprises one or more production templates where each template produces well fluids through manifold headers that are connected to one or more pipelines. The pipelines transport well fluids to an onshore terminal, an offshore platform or any other receiving facility for further processing. Processed gas and condensate are exported to the market. One or more umbilicals for power, control and utility supplies are installed from the receiving facility to the subsea installation.
For the initial production phase, well fluids may flow into the receiving facility by means of the reservoir pressure. Later in the productions phase or at start-up of the production, well fluid boosting is required in order to maintain the production level and to recover the anticipated gas and condensate volumes. This is may be performed by a subsea compressor assembly. Subsea compressors for this purpose with electric motors that requires a dry environment, and that utilizes a pressurised, gas filled motor housing are for instance disclosed in Norwegian Patents Nos. NO 172075, NO 173197, Norwegian Patent Application No. 2001 5199 as well as Norwegian Patent Application No. 2003 3034.
These publications disclose the use of gas filled electric motors where avoiding corrosion and other problems that are related to separation of hydrocarbon condensates and water in liquid form in the motor, is considered.
Norwegian Patent Application 2003 3034 discloses a gas compressor module with a pressure housing. The module includes an electric motor and a compressor connected with at least one shaft. The shaft is carried by magnetic bearings. The application describes volume and pressure control of the gas flowing into the motor, and the use of a supply of dry hydrocarbon gas. Furthermore means for sensing the pressure in the inlet and outlet is described, whereby based on the measured pressure, the pressure and volume regulator controls the pressure for injection of gas from the supply into the motor housing.
The application does however not solve the problem with how to handle mercury in the gas flow, and how to provide a sufficiently dry gas for the use as a pressure medium in the compressor station components.
This is achieved with the system according to the present invention defining a gas conditioning unit for conditioning a well stream. The well stream includes a hydrocarbon gas, and this gas is conditioned to a substantially dry gas for use in subsea components. The gas must be processed or conditioned to remove solid particles and liquids suspended in the gas, as the gas is to be used in components requiring a controlled environment in a pressure housing. Gas is frequently introduced in pressure housings for components to provide cooling of the components, to avoid corrosion, to prevent of unfavourable external influence by ingress of water etc. The gas conditioning unit includes a hydro cyclone separator and a water separation filter.
The gas conditioning unit may further include a screen unit with a silver surface for the gas to pass through to act as an anode for mercury content in the gas. Many components, in particular components used in connection with electricity are made of copper, and when copper is used mercury should be avoided. Furthermore, accumulation of mercury may cause short circuits in electric components.
The gas conditioning unit may further included an inlet in fluid connection with the outlet of the compressor and a liquid outlet in connection with a liquid side of an inlet liquid separator. A gas outlet in of the compressor may be in connection with a gas side of an inlet liquid separator of the compressor, performing the main separation of the gas and the liquid components of the well flow before the gas enters the compressor to avoid two phase compression.
The water separation filter may be a coalescing filter.
A subsea compression module may include an electric motor and a compressor with an inlet and an outlet, driven by the motor for pressurising at least a part of the well stream. A conditioning unit includes a hydro cyclone separator and a water separation filter for conditioning the pressurised well stream to a substantially dry clean gas. The gas is intended for compressing subsea components in a pressure chamber requiring a controlled environment.
The subsea components may include the motor driving the compressor.
The subsea components may include a motor driving a pump for the liquid phase of the well stream. The subsea components may include the motor driving the compressor, the compression module may be a natural gas well flow pressure boosting station, and the conditioning unit may be adapted to only condition a fraction of the total compressed well flow.
The compressor may be a multistage compressor, and the gas to the conditioning unit may be is taken from an intermediate stage of the compressor.
Known from previous patent applications Joule Thomson valves has been used for liquid separation in gas conditioning units. However, as the gas might contain fines and sand it is foreseen that the valve will be exposed to heavy erosion. For this reason the use of cyclone separators is introduced to separate the remaining particles, which have not been separated out in an inlet scrubber prior to entering the system.
To accommodate the best possible control and function of the gas conditioning unit it is of the most importance that the pressure loss over the cyclone separator is as low as possible. As the gas enters into the cyclone separator the higher density fluid and fines separates from the gas and goes to the bottom before being routed back in to the inlet scrubber. In the same operation the gas with the less density will exit the cyclone separator on the top, entering into the water separation filter for the final cleaning prior entering into the components of the system such as the motor, accumulator or being routed back into the scrubber.
For operational and maintenance reasons the gas conditioning unit according to the invention may be separately retrievable.
In previous patent publications no concern has been discussed with respect to impact on copper from mercury content if well stream gas. To handle this, the gas-conditioning unit may further include a vessel unit with a silver surface and or silver mesh for the gas to pass through which will act as a sacrificial anode for the mercury content in the gas. The dimensioning of the gas exposed silver surface will be dependant of the mercury content in the gas being feed through the gas conditioning unit.
The introduction of the silver mesh is to reduce the impact of the mercury in particular on copper components such as windings and connections in a motor.
The gas conditioning unit may include an inlet in fluid connection with the outlet of the compressor, and a liquid outlet in connection with a liquid side of an inlet liquid separator. A pump may have to be used to pump liquid from the conditioning unit into the liquid separator. A gas outlet may be connected to a gas side of the inlet liquid separator.
The system may be used in conjunction with a separate coupling chamber separated from the compressor and the motor by seals, which includes a separate specifically controlled pressure. This pressure is controlled to be higher than the pressure in the motor chamber and lower than the suction pressure of the compressor.
A subsea compression station where this system may be included may comprise the following modules and parts: one or more compressor trains, one or more circuit breaker modules, inlet and outlet manifolds, inlet coolers (if supply pipelines not are sufficient for cooling the well stream), inlet sand trap (for accidental sand production), parking location for main transformer and power umbilical termination head, prosess system, control system. The compressor train may include: compressor module, compressor variable speed drive (VSD), anti surge valve and actuator, anti surge cooler, separator/scrubber module, pump module, pump VSD (variable speed drive), remote and manually operated valves, interconnection piping, control system including control modules.
The compressor may be driven directly by high-speed motor. The electric motor may be cooled with a hydrocarbon gas at a pressure controlled to be equal or close to the suction pressure of the compressor. The gas source is the well stream supplied to the subsea compression station, and the gas must be conditioned prior to entering the electric motor. The material properties of the compressor unit should be suitable for operation with relevant contents of H2S and CO2.
The compressor and the material properties should be designed for the liquid fractions and solids content coming with the gas stream from an upstream separator. The size and distribution of liquid droplets and solids particles are dependent on the separator design, and the separator should be designed to bring the content of liquids and solids down to an acceptable level. The compression system may be designed to handle the continuous fines/sand production. The rotating equipment may be protected against wear and degradation from solids to ensure high efficiency, long life and reliability.
The compressor may include an anti-surge control recycle line designed for full recycle flow at maximum conditions speed (105%). The anti-surge control valve may be an electrically actuated, axial stroke design and may be located close to the compressor discharge at high point. An anti-surge recycle cooler may be included downstream of the anti-surge valve in the recycling pipe loop. The compressors may have a discharge pipe equipped with a remote operated isolating valve. A non-return valve may be fitted in the compressor discharge pipe upstream of the isolation valve.
The separator separates liquid/solids from the gas, which in turn is ingested into the pump and compressor, respectively. The separator is designed to separate liquids and solids from the gas flow to avoid excessive erosion of the compressor, and to ensure clean dry gas to the various chambers, including the motor chamber and the compressor chamber. The separator is designed to ensure that solids not are clogged or undesirably accumulated anywhere in the separator.
The compression station may include various process coolers such as an anti surge cooler/recycle cooler to cool the gas flow in the anti surge line (compressor recycle loop) and input coolers to cool the flow from templates.
The compressor station may have tie-in connections for well fluid discharge, and may include ROV or remotely operated valves for routing of the well fluid to the different pipelines.
The well fluid from tied-in production templates may be distributed to a separator equipped with a remotely actuated isolation valve in the inlet pipe, this being either a hydraulicaily or electrically actuated valve. The well stream may further be routed via the compressor by-pass line before compressor start up and the by-pass valve may be closed when the compressors are brought into operation. Most of the solids from the production may be removed in separators. Sand/fines/solids entering the compression station will be separated out in the separator and transported via the liquid pump to the discharge pipeline. However, a sand trap for accidental sand production may be used to remove sand from the inlet well fluid. Gas demisting and gas-liquid separation may be performed by the use of scrubbers.
Brief description of the enclosed drawing:
Fig. 1 is a schematic representation of a subsea compression module with a gas conditioning unit according to an embodiment of the invention.
Detailed description of embodiments of the invention with reference to the enclosed figure:
Fig. 1 shows a subsea compressor module according to an embodiment of the invention. The module includes an electric motor 1 , a coupling chamber 2 or intermediate chamber and a compressor 3. The motor 1 is connected to the compressor 3 with a coupling K in the coupling chamber 2. Alternatively motor 1 and the compressor 3 may be connected to the same shaft. The coupling K may for instance be a flange or any other suitable joint. Alternatively the coupling chamber 2 may include a transmission if a certain ratio is needed between the motor 1 and the compressor 3.
A seal T1 is provided on the output shaft of the motor, where the shaft enters the coupling chamber. Similarly, a seal T2 is provided on the input shaft of the compressor where this shaft enters the coupling chamber.
An inlet liquid separator 5 receives a well flow and delivers a substantially dry gas to the compressor at a pressure P1.
A line L3 from the separator 5 controls the differential pressure between the liquid separator 5 and the supply line from the gas conditioning unit Pr ensuring that the motor pressure Pm is maintained at a higher level than P1. A line L4 connects the coupling chamber 2 and the liquid separator 5. A valve V1 ensures that the pressure Pk in the coupling chamber 2 is less than the pressure Pm in the motor chamber.
A line L1 from the well and into the compressor 3 is at a suction pressure P1. The compressor delivers a compressed outlet fluid flow through line L2. There is also a inter-stage pressure taken from the compressor feeding into the gas conditioning unit 6.
The motor and the compressor are connected with a shaft and a coupling K placed inside the coupling chamber 2. The pressure housing for motor 1 includes electric connections and lines for supply of clean/conditioned gas.
The coupling chamber 2 receives gas leaking from the compressor 3 through seal T2. From the motor side, the coupling chamber 2 can receive gas that leaks through seal T1 from the motor as the pressure in the motor Pm is above the pressure in the coupling chamber Pk and above the suction pressure P1 of the compressor.
The coupling chamber 2 includes connections for an outlet L4 for fluids leaking from the motor chamber 1 and the compressor chamber 2.
To ensure that the pressure Pm in the motor chamber 1 is higher than the pressure in the coupling chamber Pk, a pressure sensor or probe is placed in the inlet liquid separator 5 and in the coupling chamber Pk for monitoring the respective pressures and a further pressure controller Pr controls the pressure of the gas in the motor chamber 1 from the conditioning unit 6. This ensures that the pressure in the motor chamber Pm is maintained at a higher level than the suction pressure P1 of the compressor and the pressure Pk in the coupling chamber. Leaking gas with a pressure P3 is returned to the suction side or the liquid separator to prevent collection of impure gas in the sealing system for the motor. The seals T1 and T2 may be of various types, and may for instance be brush seals or labyrinth seals, both types being well known within the field. The liquid separator 5 ensures a single phase flow to the compressor. Water separation filters may also be included.
The motor chamber is supplied with a conditioned gas from the main process conditioning unit 6. The conditioning unit 6 ensures that that the gas entering the motor chamber not is more polluted than the inner components can tolerate.
The conditioning unit 6 utilizes a hydro cyclone and a water separation filter. The unit may also include a screen, grid or mesh covered with, or made of, silver for the gas to pass through to form an anode for mercury. Any structure allowing contact between the gas and the metal may be used. The conditioning unit may receive fluid at high or intermediate pressure from the compressor.
The pressure sensor placed in the inlet liquid separator 5 and in the coupling chamber 2, registers the respective pressures and ensures that the pressure Pm in the motor chamber is above the pressure in the coupling chamber. The pressure regulator Pr controls the pressure of the gas inn to the motor chamber from the conditioning unit 6 at a pressure P4. This ensures that the pressure Pm in the motor chamber is above the inlet or suction pressure P1 of the compressor and the pressure Pk in the coupling chamber.
Gas taken at a pressure P4 from the conditioning unit 6 is led to the pressure regulator Pr through line L5 for further delivery of gas to the motor at pressure Pm. Gas from the conditioning unit 6 may be supplied to the liquid separator 5. The pressure regulator Pr is also connected to the liquid separator through Line L3. Conditioned gas not utilised by the motor is routed back into the liquid separator 5.

Claims

Claims:
1. A gas conditioning unit (6) for conditioning a well stream including a hydrocarbon gas to a substantially dry gas for use in subsea components requiring a controlled environment in a pressure housing for being pressurized with a pressure (Pm), characterized in that it includes a hydro cyclone separator and a water separation filter.
2. The gas conditioning unit (6) according to claim 1 further comprising a screen unit with a silver surface for the gas to pass through to act as an anode for mercury content in the gas.
3. The gas conditioning unit (6) according to claim 1 further comprising an inlet in fluid connection with the outlet of the compressor; a liquid outlet in connection with a liquid side of an inlet liquid separator (5); and a gas outlet in connection with a gas side of the inlet liquid separator (5).
4. The gas conditioning unit (6) according to claim 1 wherein the water separation filter is a coalescing filter.
5. A subsea compression module with an electric motor (1) and a compressor (3) with an inlet (L1) and an outlet, driven by the motor (1) for pressurising at least a part of the well stream, characterized in a conditioning unit (6) including a hydro cyclone separator and a water separation filter for conditioning the pressurised well stream to a substantially dry clean gas for compressing subsea components in a pressure chamber requiring a controlled environment.
6. A subsea compression module according to claim 5 wherein the subsea components includes the motor (1) driving the compressor (3).
7. The subsea compression module according to claim 5 wherein the sub- sea components includes the motor (1) driving a pump for the liquid phase of the well stream
8. A subsea compression module according to claim 5 wherein the subsea components includes the motor (1) driving the compressor (3); the compression module is a natural gas well flow pressure boosting station; and the conditioning unit (6) is adapted to only condition a fraction of the total compressed well flow
9. A subsea compression module according to claim 7 wherein the compressor (3) is a multistage compressor, and where the gas to the conditioning unit (6) is taken from an intermediate stage of the compressor.
PCT/NO2006/000409 2005-11-11 2006-11-10 Unit for gas treatment in rotating equipment for subsea compression WO2007055591A1 (en)

Applications Claiming Priority (2)

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NO20055357 2005-11-11
NO20055357A NO327542B1 (en) 2005-11-11 2005-11-11 Unit for conditioning a well stream and an underwater compression module.

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Cited By (2)

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WO2012058069A2 (en) 2010-10-27 2012-05-03 Dresser-Rand Company System and method for rapid pressurization of a motor/bearing cooling loop for a hermetically sealed motor/compressor system
EP2683944A1 (en) * 2011-03-07 2014-01-15 Aker Subsea AS Subsea motor-turbomachine

Citations (4)

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US5673752A (en) * 1995-12-22 1997-10-07 Scudder; Pat Method and apparatus for producing gas from a formation containing both gas and water
WO1998019040A1 (en) * 1996-10-25 1998-05-07 Northland Production Testing Ltd. Recovery of gas from drilling fluid returns in underbalanced drilling
WO2003033871A1 (en) * 2001-10-12 2003-04-24 Alpha Thames Ltd System and method for separating fluids
WO2005026497A1 (en) * 2003-09-12 2005-03-24 Kværner Oilfield Products A.S. Subsea compression system and method

Patent Citations (4)

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Publication number Priority date Publication date Assignee Title
US5673752A (en) * 1995-12-22 1997-10-07 Scudder; Pat Method and apparatus for producing gas from a formation containing both gas and water
WO1998019040A1 (en) * 1996-10-25 1998-05-07 Northland Production Testing Ltd. Recovery of gas from drilling fluid returns in underbalanced drilling
WO2003033871A1 (en) * 2001-10-12 2003-04-24 Alpha Thames Ltd System and method for separating fluids
WO2005026497A1 (en) * 2003-09-12 2005-03-24 Kværner Oilfield Products A.S. Subsea compression system and method

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012058069A2 (en) 2010-10-27 2012-05-03 Dresser-Rand Company System and method for rapid pressurization of a motor/bearing cooling loop for a hermetically sealed motor/compressor system
EP2633198A4 (en) * 2010-10-27 2017-01-11 Dresser-Rand Company System and method for rapid pressurization of a motor/bearing cooling loop for a hermetically sealed motor/compressor system
US9726196B2 (en) 2010-10-27 2017-08-08 Dresser-Rand Company System and cooling for rapid pressurization of a motor-bearing cooling loop for a hermetically sealed motor/compressor system
EP2683944A1 (en) * 2011-03-07 2014-01-15 Aker Subsea AS Subsea motor-turbomachine
EP2683944A4 (en) * 2011-03-07 2014-10-22 Aker Subsea As Subsea motor-turbomachine

Also Published As

Publication number Publication date
NO20055357L (en) 2007-05-14
NO327542B1 (en) 2009-08-10
NO20055357D0 (en) 2005-11-11

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