WO2016075018A1

WO2016075018A1 - A multiphase fluid separation and boosting system

Info

Publication number: WO2016075018A1
Application number: PCT/EP2015/075748
Authority: WO
Inventors: John Daniel Friedemann; Giacomo Landi
Original assignee: Vetco Gray Scandinavia As
Priority date: 2014-11-10
Filing date: 2015-11-04
Publication date: 2016-05-19
Also published as: NO20141349A1; NO338639B1

Abstract

A subsea boosting system for multiphase well fluid, the boosting system comprising a dynamic separator (12) and a booster unit (39, 41) coupled in axial alignment, wherein the booster unit is coupled to the separator via a stationary multiphase transition piece (13) arranged for routing a separated fluid phase (0; G) in continuous axial flow from the separator to the booster unit.

Description

A MULTIPHASE FLUID SEPARATION AND BOOSTING SYSTEM

TECHNICAL FIELD OF THE FNVENTION

The present invention relates to a system arranged for boosting the pressure in a multiphase fluid. More precisely, the invention relates to a system arranged for boosting the pressures in liquid and gas phases which are separated out from a multiphase fluid in the process of recovery, treatment and transportation of hydrocarbon fluid from a subsea well.

BACKGROUND AND PRIOR ART

Transfer of oil and gas from a subsea well to a topside recipient involves operation of pumps and compressors to drive the fluid through sometimes distant pipelines and via long risers from seafloor to surface. Gas compressors, including wet tolerant or wet gas compressors, can handle liquid to a limited extent only. Pumps on the other hand can handle larger volumes of gas in the fluid. However, the capacity of a multiphase fluid pump reduces significantly at higher gas volume fractions, due to phase separation effects. Use of separators in subsea boosting stations enables to optimize the operation of pumps and compressors, making them work closer to the best efficiency point.

Separators used in subsea boosting can be divided into passive and active or dynamic separators. The passive separator typically relies on gravity to cause the heavier fraction to accumulate in a bottom zone of the separator. The dynamic separator is driven to generate rotation in the fluid by which the heavier fraction is forced to accumulate in a peripheral zone of the separator due to centrifugal or cyclonic action.

Considering that individual separators for liquid/solids separation, gas/liquid separation and liquid/liquid separation, e.g., may be required it is readily seen that a subsea boosting station can be a relatively complex installation including separator(s), pump, compressor, manifolds, jumpers/pipings and valves, in total generating a substantial footprint on the seafloor. SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a subsea boosting system of less complex nature and which requires a reduced installation space and area.

It is an object of the present invention to provide a compact boosting system that reduces and simplifies the layout of a subsea boosting station.

It is another object of the present invention to provide a flexible boosting system by integration of components for power and flow generation.

It is yet another object of the present invention to provide a subsea boosting system which can be readily upside or downsized through modularization of components for separation and pressure boosting.

According to the invention, briefly, at least one of these objects is met in a subsea boosting system for multiphase well fluid, the boosting system comprising a dynamic separator and a booster unit coupled in axial alignment, wherein the booster unit is coupled to the separator via a stationary multiphase transition piece arranged for routing a separated fluid phase in continuous axial flow from the separator to the booster unit.

One advantageous embodiment comprises a dynamic separator coupled in axial relation with a helicon-axial pump and a wet gas compressor via interconnecting stationary transition pieces that provide continuous axial flow of a separated lighter fluid phase through all interconnected units.

The compactness of the system is ensured by integration of a power and flow module to operate the units of the system.

Embodiments of the subsea boosting system comprise separator and booster units at least one of which comprises a motor that is integrated in a power and flow module.

The power and flow module can be integrated in booster units such as a booster pump or a wet tolerant gas compressor. More precisely, the power and flow module is an electrically powered machine which can be realized in different embodiments. Common to all embodiments is an integrated permanent magnet (PM) motor wherein permanent magnets are carried in the periphery of a rotor whereas electromagnets and stator coils are supported on a stationary casing that surrounds the rotor.

Embodiments of the invention comprise a power and flow module wherein the rotor is formed with radial blades or vanes which are attached to a central rotor shaft that is journalled for rotation. Other embodiments comprise a rotor with vanes that are journalled for rotation on the exterior of a stationary shaft. The rotor is designed for axial displacement of fluid through the power and flow module. Embodiments of the invention comprise a power and flow module wherein the rotor vanes are provided a pitch angle against the flow direction which is applied to generate a mainly axial flow, without a significant radial component, through the processing unit. Other embodiments comprise a rotor designed to apply a significant radial component to the flow through the processing unit.

In one embodiment of the subsea boosting system, the separator comprises the power and flow module drivingly connected to a screw or impeller which generates separation of fluid phases through centrifugal or cyclonic action.

In another embodiment, the separator comprises the power and flow module integrated with a cylindrical drum which is internally formed with wings that impart a rotational motion to the flow through the drum.

In yet another embodiment of the separator, the power and flow module generates, in result of a composite curvature in its radial vanes, the rotational motion in the flow which is required to accomplish separation of fluid phases through centrifugal action. In all cases the processing unit operating as a separator can be arranged for lateral/radial discharge of a heavier fluid phase which is routed out from the axial flow, whereas a lighter fluid phase passes through the processing unit in axial direction. Routing the separated fluid phases from and between the units can be accomplished through a stationary transition piece having internal passages as well as upstream and downstream interfaces which mate with the connecting units. The transition piece typically has an upstream interface comprising an outer annular entrance for the heavier fluid phase and a central entrance, annular or circular, for the lighter fluid phase radially inside of the outer annulus. The downstream interface has either an annular exit for heavier phase fluid or a central exit for lighter phase fluid.

The power and flow module can be applied in a booster pump or compressor. In embodiments of the booster system, the power and flow module is multiplied forming a package of axially stacked PM motors and rotors which are operated for acceleration and compression of the flow through the booster pump or compressor. Each power and flow module in the stacked configuration may be separately powered and individually controlled via dedicated variable speed drives (VSD), one for each motor stage/rotor.

Further advantages as well as advantageous features of the subsea boosting system of the present invention will appear from the following description and the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention will appear and be explained below with reference made to the accompanying schematic drawings, illustrating embodiments of the invention. In the drawings,

Fig. 1 is a longitudinal sectional view through a set of power and flow modules adapted for incorporation in a subsea boosting system according to the present invention,

Fig. 2 is a corresponding sectional view illustrating the power and flow module applied in a centrifugal separator,

Fig. 3 is corresponding sectional view illustrating the power and flow module applied in a booster pump, Fig. 4 is a corresponding sectional view illustrating the power and flow module applied in a wet gas compressor,

Figs. 5a-5c illustrate the power and flow module applied in alternatively configured separators, Fig. 6 is a longitudinal sectional view through an integrated and compact boosting system according to the present invention, and

Fig. 7 is a view corresponding to Fig. 6 showing an alternative embodiment of the boosting system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to Fig. 1 a set of power and flow modules 1 is shown in longitudinal sectional view. Each power and flow module 1 comprises a rotor 2 which is journalled for rotation on a rotor shaft 3. The rotors 2 can be individually journalled in radial/axial bearings 4 onto the exterior of a stationary rotor shaft for rotation thereabout separately from other rotors in a set of power and flow modules. These bearings 4 can be of a kind which gets lubrication from the process fluid.

The rotors may alternatively be non-rotationally attached to a common rotor shaft which is journalled to rotate in bearings arranged on a bearing support (not shown).

Each rotor 2 comprises a set of rotor blades or rotor vanes 5 that extend mainly in radial directions from a rotor centre axis C. At least some of the rotor vanes 5 carry a permanent magnet 6 in the outer, peripheral end of the rotor vane. The permanent magnets 6 can be integrated in a ring member 7 interconnected to the rotor vanes in the rotor periphery 8.

The rotor 2 is surrounded by a casing 9 which has coupling means, such as flanges 10, for coupling to adjacent power and flow modules 1. Seals, not shown in the drawings, may be arranged as required in the meeting interfaces between casings of coupled power and flow modules. Supported in the casing 9 is a set of electromagnets with associated stator coils, in the drawings commonly referred to by reference no 11. The electromagnets 11 form an outer ring about the inner ring of permanent magnets. The casing 9 can take the shape of a cylinder.

The rotor 2 is thus brought in rotation as the permanent magnets move in the magnetic field which is generated when current is fed to the stator coils for energizing the electromagnets.

In rotation the power and flow module 1 effects basically an axial flow through an annular flow passage defined by the rotor or the rotors of the power and flow module or the set of power and flow modules. The rotor vanes 5 are designed with an angle of attack or pitch angle against the flow F and relative to the centre axis C. In a set of power and flow modules at least one of the rotors may have vanes with other pitch angle than the other rotors in the set. The pitch angles can be successively increased or decreased from the first to the last rotor in the set, in order this way to change flow and/or pressure in the fluid.

In order to further customize the operation each power and flow module 1 in a set of power and flow modules can be individually powered and separately controlled via dedicated variable speed drives as illustrated through the VSD boxes in Fig.1.

If appropriate, the power and flow module or set of power and flow modules can be arranged to comprise contra rotating rotors such that each clockwise rotating rotor follows upon an anti-clockwise rotating rotor. Also if appropriate each power and flow module can be arranged to follow directly upon a preceding module without inter-positioned stator vanes between the rotor vanes of successive power and flow modules.

Embodiments of the power and flow module 1 can be modified to impart a radial component to the flow. To this purpose modified rotor vanes (see rotor vanes 5' in Fig. 2) can be shaped with an angle of attack or curvature in the radial view, the rotor vanes being curved backwards with respect to the rotational direction of the rotor. In a set of power and flow modules some of the rotors may be designed to generate axial flow mainly, whereas other rotors are designed to generate rotation in the flow in order to subject the fluid to centrifugal force and cyclonic action.

Fig. 2 illustrates the power and flow module 1 implemented in a boosting system unit operating as a separator 12. It should be noted that even if the drawing of Fig. 2 depicts two power and flow modules only, the actual number of power and flow modules 1 can be one only or multiplied and adapted to operational requirements. For example, the separator 12 may comprise an upstream group of power and flow modules configured for generation of axial flow, whereas a successive and downstream group of power and flow modules may be configured to impart rotational motion in the flow by means of radially curved or double-curved rotor vanes 5 ' .

In the separator 12 the rotational motion that is imparted to the flow causes separation of fluid phases due to cyclonic action, as the heavier fluid phase is urged by centrifugal force to accumulate in a peripheral region of the annular passage through the power and flow modules. Coupled to the downstream end of the separator, a stationary transition piece 13 provides passages 14 and 15 for routing the heavier fluid phase O to a radial or lateral discharge, as well as passages 16 and 17 for routing the lighter fluid phase G to an axial, central discharge. In the upstream interface the transition piece 13 has an annular outer entrance 18 for the heavier phase and an annular inner entrance 19 for the lighter fluid phase. The entries 18 and 19 can be separated upstream by a cylindrical divider ring 20. A spool piece 21 with no moving internals can be inserted between the power and flow modules 1 and the transition piece 13, if appropriate.

The power and flow module 1 can be implemented in separator units of other and alternative configuration. With reference to Fig. 5a, a boosting system unit operating as a separator 12' is illustrated, comprising a cylindrical drum 22 which is supported rotationally inside a cylinder 23, the cylinder 23 being stationary. The drum can be rotationally journalled in bearings 24 and 25 arranged at the ends of the drum and cylinder. The drum is installed in a multiphase fluid flow F to receive mixed fluid phases via an inlet end 26 and to discharge separated fluid phases O, G via an outlet end 27. Separation of the fluid phases is accomplished by imparting rotational motion in the fluid upon passage through the drum 22.

Rotational motion can advantageously be generated by one or several power and flow modules 1 which are integrated in the separator 12' and installed across the fluid flow through the separator. More precisely, the electromagnets 11 are supported on the stationary cylinder 23, whereas the permanent magnets 6 are supported on the drum 22. The drum is thus brought in rotation as the permanent magnets move in the magnetic field which is generated when current is fed to the stator coils for energizing the electromagnets. Rotational motion can be imparted to the flow via one or more wings 28 which is/are arranged projecting inwards from the wall of the drum, the wings running mainly in the longitudinal direction of the drum. The wings 28 can have any suitable sectional shape. The internal wings may be oriented in parallel with the longitudinal centre of the drum, as illustrated by the straight dotted line in Fig. 5b. The wings may alternatively be oriented at an angle a relative to the centre line as illustrated through the line 28 in Fig. 5b. The wings may also be shaped to follow a helical curve in the inner periphery of the drum 22 as illustrated through the curved dotted line in Fig. 5b.

Yet an alternative implementation of the power and flow module 1 in a boosting system unit operating as a separator is disclosed with reference to Fig. 5c. The separator 12" of Fig. 5c comprises a stationary outer cylinder 29 in surrounding relation about a stationary inner cylinder or drum 30. The inner drum 30 has a perforated wall wherein openings or slits 31 are formed to permit transfer of a heavier fluid phase from the drum to an annular space 32 defined between the drum and the outer cylinder. A lateral discharge 33 is connected to the annular space 32 in radial direction.

A screw 34 is journalled for rotation internally in the drum. The internal screw 34 has a radial blade 35 running helically about a screw shaft 36. The screw shaft 36 is drivingly connected to the rotor shaft of one or several stacked power and flow modules 1. The non-driven end of the screw is journalled in a bearing support 37 arranged in the downstream end of the separator. The boosting system unit operating as a separator 12, 12' or 12" can be connected to a downstream booster unit via an inter-coupled transition piece, such as the stationary transition piece 13 of Fig. 2. However, whereas the transition piece 13 depicted in Fig. 2 is arranged to route the heavier phase out of the axial flow that continues through the coupled units, another and alternative transition piece 13', see Fig. 3, is arranged to route the lighter phase G out of the axial flow while the heavier phase O continues axially along an annular passage 38 into the successive booster unit in the line.

The transition piece 13' may be succeeded in the flow direction by a booster unit configured to operate as a booster pump 39. In the booster pump 39, power and flow modules 1 are powered to accelerate the fluid, thus increasing flow and/or pressure towards a discharge end of the booster pump. A discharge piece and radial collector 40 is coupled to the downstream end of the booster pump, routing the flow out of the process line. In that sense, the discharge piece 40 may terminate the axial flow through the boosting system. Fig. 4 illustrates a modified power and flow module incorporated in a boosting system unit operating as a wet tolerant gas compressor 41. The power and flow module of Fig. 4 differs from the power and flow module 1 with respect to the shape of the rotor vanes. Instead of the vanes forming the rotor 2 in the power and flow module 1, the rotor 42 in the power and flow module comprises a set of stacked turbine wheels 43 rotating about an axle 44. Stationary transition pieces 45 route the fluid to the successive turbine stage.

Fig. 6 shows an implementation of the power and flow module 1, in a highly integrated and compact embodiment of the subsea boosting system. In the embodiment of Fig. 6 a dynamic separator 12 is coupled in axial relation with a wet gas compressor 41 through an interconnecting transition piece 13. The separator 12 effects separation of fluid phases through cyclonic or centrifugal action which is driven by the rotors 2 of a set of integrated, power and flow modules 1. A gas phase is routed in axial direction through the transition piece 13 to the central inlet 46 of the wet tolerant gas compressor 41 which compresses the gas through centrifugal action driven by the rotors 42 of a set of integrated, power and flow modules 1 '. Fig. 7 shows another implementation of the power and flow module 1, in a highly integrated and compact embodiment of the subsea boosting system. In the embodiment of Fig. 7 a dynamic separator 12 is coupled in axial relation with a wet gas compressor 41 through an interconnecting transition piece 13 and with a helicon- axial pump 39. The separator 12 effects separation of fluid phases through cyclonic or centrifugal action which is driven by the rotors 2 of a set of integrated, power and flow modules 1. A lighter phase such as a gas phase G is routed in axial direction through a transition piece 13 and downstream via the hollow stationary rotor shaft 3 to the central inlet 46 of the wet tolerant gas compressor 41 which compresses the gas through centrifugal action driven by the rotors 42 of a set of integrated, power and flow modules . The heavier phase O is routed to the pump and is then discharged via the radial collector 40.

It has been explained above and illustrated in drawings of exemplifying embodiments, that a highly integrated and compact boosting system for recovery, treatment and transportation of subsea hydrocarbon well fluids can be achieved by implementation of the teachings presented herein.

Still, it will be appreciated that modifications of the disclosed embodiments are possible without leaving the scope and spirit of the invention as disclosed above and defined in appended claims.

Claims

CLAIMS:

1. A subsea boosting system for multiphase well fluid, the boosting system comprising a dynamic separator (12, 12', 12") and a booster unit (39, 41) coupled in axial alignment, characterized in that the booster unit is coupled to the separator via a stationary multiphase transition piece (13, 13') arranged for routing a separated fluid phase (O; G) in continuous axial flow from the separator to the booster unit.

2. The boosting system of claim 1 , wherein at least one of the separator (12, 12', 12") and the booster unit (39, 41) comprises a motor integrated in a power and flow module (1, 1 ').

3. The boosting system of claim 2, wherein the power and flow module (1, 1 ') is integrated in a booster pump (39) and/or in a wet tolerant gas compressor (41).

4. The boosting system of claim 2 or 3, wherein the power and flow module (1 , ) is an electrically powered flow machine wherein permanent magnets (6) are carried in the periphery of a rotor (2, 22, 30, 42), whereas electromagnets (11) and stator coils are supported on a stationary casing that surrounds the rotor.

5. The boosting system of claim 4, wherein the rotor (2) of the power and flow module (1) comprises rotor vanes (5) which are provided a pitch angle against the flow direction (F) which is applied to generate a mainly axial flow, without a significant radial component.

6. The boosting system of claim 4, wherein the rotor (2) of the power and flow module (1) comprises rotor vanes (5') which are curved backwards with respect to the rotational direction to apply a significant radial component to the flow.

7. The boosting system of claims 5 and 6, wherein the rotor of the power and flow module comprises double curved rotor vanes.

8. The boosting system of claim 4, wherein the rotor (42) of the power and flow module (1 ') is a turbine wheel (43).

9. The boosting system of any of claims 5 to 7, wherein in the dynamic separator (12") the power and flow module (1) is drivingly connected to a screw or impeller (34) that is rotationally journalled in a cylinder (30) which communicates with an external annulus (32) into which liquid is forced through centrifugal action via slots (31) formed through the cylinder wall.

10. The boosting system of any of claims 5 to 7, wherein in the dynamic separator (12') the power and flow module (1) is integrated with a cylindrical drum (22) which is internally formed with wings (28) that impart a rotational motion to the flow through the drum.

11. The boosting system of any previous claim, comprising a stationary transition piece (13, 13') arranged for interconnection of successively coupled separator (12, 12', 12") and booster units (39,41), the transition piece internally formed with separate routes for lighter (G) and heavier (O) fluid phases.

12. The boosting system of claim 11 , wherein a lighter phase (G) is routed through the stationary multiphase transition piece (13) via a central passage (17), wherein the central passage (17) connects to an inlet of a centrifugal wet gas compressor (41).

13. The boosting system of claim 11 or 12, wherein a heavier phase (O) is routed through the stationary multiphase transition piece (13') via an annular passage (38), wherein the annular passage (38) is connected to an intake of a booster pump (39).

14. The boosting system of any previous claim, wherein the separator and/or the booster unit comprises a set of integrated power and flow modules (1 , ) arranged in succession, and further wherein each power and flow module (1, ) is individually controlled via a dedicated variable speed drive (VSD).

15. The boosting system of claim 14, wherein the set of power and flow modules (1, ) comprises contra rotors such that each clockwise rotor follows upon an anticlockwise rotating rotor and wherein each power and flow module (1) follows directly upon a preceding module without inter-positioned stator vanes between the rotor vanes of successive power and flow modules (1).