NO20141341A1 - Process and system for pressure control of hydrocarbon well fluids - Google Patents

Abstract

A method and system are described, adapted for pressure control of well fluid produced from wells in a hydrocarbon production field. The system comprises a first pump (6) in fluid communication with a first well (W1-W5) and a second pump (6) in fluid communication with a second well (W1-W5), wherein the pumps are arranged to receive well fluid produced from the respective wells. the wells, and to deliver the fluid to downstream piping (P1-P5) or equipment. The first and second pumps each comprise a motor / generator unit which can operate as a generator when the pump is powered by well fluid in power generation mode, and as a motor when the motor / generator unit operates in power consumption mode, the pumps being operatively interconnected via a power distribution unit ( 8) configured to distribute recovered power between the pumps or other receivers.

Description

Method and system for pressure regulation of hydrocarbon well fluids

The present invention relates to a method and a system which is designed for pressure regulation of well fluids during hydrocarbon production. The invention relates in particular to a system which seeks to achieve a reduction in power consumption and recovery of energy in rotating equipment that is used in the production and transport of hydrocarbon fluid from wells to reception on the surface.

Background of the invention and prior art Hydrocarbon wells in a hydrocarbon production field typically produce at different pressures and flow rates at a given time. The individual oil or gas well usually also delivers with a flow rate and pressure that become lower over time. Changes in well fluid pressure and regulation of flow rate and pressure in produced well fluid are conventionally handled by throttling or increasing the flow, i.e. if the well fluid pressure is higher than desired in downstream equipment, the flow is limited by means of a throttling valve arranged on the wellhead, and if the well fluid pressure is lower than that required for transport or downstream treatment, the flow can be increased by means of a pressure booster pump or compressor arranged downstream of the choke valve. Pressure boosting and throttling are processes that either consume energy or that reduce the potential production rate from wells in a

hydrocarbon production field.

Summary of the Invention

It is an object of the present invention to provide for pressure regulation of well fluids produced from wells in a hydrocarbon production field.

It is another object of the present invention to provide a power-saving method and system designed for pressure regulation of well fluids produced from wells in a hydrocarbon production field.

It is yet another object of the present invention to provide a method and a system which is designed for pressure regulation and for optimizing production from wells in a hydrocarbon production field.

It is a further object of the present invention to provide a method and a system which is designed for pressure regulation and for balancing the outlet pressure between wells in a hydrocarbon production field.

At least one of the above-mentioned objectives is achieved in a system designed for pressure regulation of well fluid produced from wells in a hydrocarbon production field where the system comprises the following: - a first pump in fluid communication with a first well and a second pump in fluid communication with a second well , where the pumps are arranged to receive well fluid produced from respective wells and to deliver the fluid to pipelines or equipment downstream, - first and second pump each with its own motor/generator unit that can operate as a generator when the pump is powered by well fluid in power generation mode , and in that the pump can operate as a power consumer by operating the motor/generator unit as a motor, in that the pumps are operationally connected via a power distribution unit that is configured to distribute recovered power between the pumps or to other receivers.

In embodiments of the invention, the following applies:

The pump can be designed as a helico-axial pump adapted for pressure increase in multiphase fluid.

The pumps are configured with a motor-generator unit that has a motor integrated into a power and flow module.

The power and flow module is an electrically driven flow machine, where permanent magnets are mounted in the circumference around a rotor at the same time as electromagnets and stator windings are mounted on an enclosure that surrounds the rotor.

The rotor in the power and flow module comprises rotor blades inclined to the direction of flow and serves to generate an essentially axial flow through the power and

the flow module.

Each of the pumps in the pressure regulation system can comprise a set of integrated power and flow modules arranged in sequence, as each power and flow module can be individually controlled via a dedicated frequency converter (Variable Speed Drive - VSD).

The set of power and flow modules in a pump may comprise counter-rotating rotors, so that each clockwise-rotating rotor follows a counterclockwise-rotating rotor.

In a set of power and flow modules, each module may be arranged to directly follow a preceding module without stator blades between the rotor blades in successive power and flow modules.

When the motor/generator unit operates as a motor, the rotor is set into rotation by the permanent magnets moving in the magnetic field created when current is applied to the stator windings to activate the electromagnets. In motor mode, the pump transfers energy to the fluid via the rotor blades, which increases the pressure in the well fluid.

When the motor/generator unit operates as a generator, the rotor is set in rotation by the well fluid, and the rotor magnets induce current in the stator windings. In generator mode, in short, the pump will absorb energy from the fluid via the rotor blades, which reduces the pressure in the well fluid. The rotor blades can be specially adapted, for example curved forwards or backwards in relation to the direction of rotation of the rotor, in order to transfer energy to the well fluid or to absorb energy from the well fluid.

In a pump comprising a set of stackable power and flow modules, the modules can be specified alternately for motor operation mode, respectively for generator operation mode. In other words, the pump can be equipped with power and flow modules that are specified alternately to transfer energy to the well fluid or to absorb energy from the well fluid, by corresponding design of the rotor blades.

The pressure regulation system according to the present invention further comprises a central power distribution unit (SPDU) which receives electrical power and control from a platform on the surface at sea or on land. The SPDU unit supplies the pumps with the necessary power, and well fluid pressure is monitored and reported to the SPDU from pressure sensors installed on each well. The SPDU contains control logic designed to determine whether the relevant pump is to be operated as a pressure boosting unit or as a pressure reducing unit, i.e. in power consumption mode or in power generation mode.

The SPDU is also equipped to receive electrical power from a pump operating in generator mode. Electrical power received in the SPDU may be shared between pumps in the pressure control system, or may be supplied to other equipment in the field, or may be supplied to platforms on the surface. In this way, the energy associated with the well fluid pressure can be balanced between wells that are connected to the pressure regulation system, while the energy consumption for pressure regulation can be reduced.

Thus, in some embodiments of the invention, the system can monitor the current well fluid pressure and report this to the power distribution unit from pressure sensors arranged on well heads.

Pumps can also be installed on wellheads and serve to equalize pressure in well fluid that is produced from wells that produce with different well fluid pressures.

Embodiments of the invention include pumps that are arranged on a module that can be connected to a wellhead, an underwater or surface valve tree.

In other embodiments, pumps can be arranged on downstream pipelines and serve to equalize pressure in fluid streams with different pressures in pipe connecting bridges/pipelines, manifolds, riser bases, PLEM or other pipelines installed at a hydrocarbon production facility.

The present invention can be implemented as a method for regulating the pressures in well fluid produced from wells in a hydrocarbon production field, the method comprising the following: - arrangement of a pump in fluid communication with the individual well to receive fluid produced from the relevant well and to deliver the fluid to downstream piping, with each pump comprising a motor/generator unit, - and increasing flow/pressure in delivered fluid by operating the pump as a motor in power consumption mode, and reducing flow/pressure in delivered fluid by operating the pump as a generator in power generation mode , so that recovered power in power generation mode is distributed between the pumps or goes to another recipient via a power distribution unit that is operationally connected to the pumps.

Details of the various aspects of the invention will be explained further below in the detailed description of preferred embodiments.

Brief description of the drawing figures

Embodiments of the invention will be explained in more detail below with reference to the attached schematic drawings. The drawings show as follows: Figure 1 shows a general design of a pressure regulation system according to the present invention, Figure 2 is a longitudinal section through power and flow modules which are adapted for incorporation in a pump for the pressure regulation system in the present invention, and Figure 3 is a corresponding sectional view illustrating a booster pump comprising a set of power and flow modules.

Detailed description of preferred designs

Although it is explained and illustrated below with reference to a subsea implementation, it is specified that the information provided here applies similarly to the process of hydrocarbon production from onshore hydrocarbon wells.

General design of a system for pressure regulation of well fluid produced from wells on the seabed at a subsea hydrocarbon production field will now be explained with reference to Figure 1. A number of wells W1-W5 distributed over the seabed 1 are connected to deliver well fluid to a platform 2 on the surface or to a vessel at sea, or to land, via pipelines P1-P5, a manifold 3 and a riser 4. A wellhead 5 at the top of each well W1-W5 is arranged to hold the valves, connections and sensors required to produce fluid from the well.

According to the embodiment of the invention shown in figure 1, a pump and generator 6 are installed in the stream downstream of a choke or production valve 7. However, the pump/generator can, as an alternative, be installed upstream of the choke/production valve 7.

The pump 6 is an electrically driven flow machine, where permanent magnets are mounted in the circumference of a rotor, while electromagnets and stator windings are mounted on an enclosure that surrounds the rotor, as will be explained in more detail below.

Electrical power is supplied to the pump 6 from a subsea power distribution unit (SPDU) 8 via a variable speed drive (VSD) 9. Power and communication between the SPDU 8 and platform 2 is transmitted via a power and control cable 10.

Electrical equipment commonly used to operate subsea units in a hydrocarbon production field, such as transformers, rectifiers, converters, etc., and which are not needed to understand the present invention, are omitted from Figure 1 for simplicity.

SPDU 8 includes control logic designed to process information about the current pressure in the well fluid that is supplied by the subsea wells W1-W5. Well fluid pressure is monitored and reported to the SPDU 8 from pressure sensors (PT) 11 located upstream of the production valves 7. The SPDU 8 uses the well fluid pressure to determine for each well whether the pump 6 should be operated to increase pressure, i.e. as a motor in power consumption mode, or to to reduce the pressure, i.e. as a generator in power generation mode.

Example

If well Wi produces with a pressure of 250 bar, the pump 6 can be operated in generator mode to reduce the pressure in fluid delivered from the pump down to e.g. 150 bar. Note that the pressure difference represents energy that would normally be wasted if the pressure were reduced by throttling the flow. If well W2 simultaneously produces with a pressure of 100 bar, pump 6 is operated in motor mode to increase the pressure in fluid delivered from the pump to 150 bar.

The energy that is recovered by reducing the pressure by

100 bar in well fluid from well Wi in this example can be of the order of 500 kW, while the energy required to increase the pressure by 100 bar in well fluid produced from well W2 can be of the same order of magnitude, around 500 kW. Balancing the pressures between the two wells as illustrated above can thus be achieved with a significant saving of energy.

The energy recovered from the pump 6 operating in generator mode is transferred to the SPDU 8 via electrical power lines 12. Control logic installed in the SPDU 8 determines whether the recovered energy should be fed to other pumps in the pressure regulation system, to other subsea power consumers or to the platform on the surface at sea or on land.

The structure with pump and generator unit 6 will now be explained in more detail with reference to figure 2.

More specifically, the pump and generator unit 6 constitute an electrically driven machine which can be of various designs. Common to all designs is an integrated permanent magnet motor (PM), where permanent magnets are mounted in the circumference of a motor rotor or paddle wheel, while electromagnets and stator windings are mounted on a stationary enclosure that encloses the rotor/paddle wheel.

Embodiments of the pump 6 comprise a power and flow module where the rotor is designed with radial blades or rotor vanes attached to a central rotor shaft which is supported for rotation. Other designs include a rotor with vanes that are mounted for rotation on a stationary shaft.

With reference to Figure 2, a set of power and flow modules 100 is shown in longitudinal section. Each power and flow module 100 comprises a rotor 101 which is supported for rotation on a rotor shaft 102. The rotor 101 can be supported in radial bearings/axial bearings 103 on the outside of a stationary rotor shaft for rotation about this, separated from the other rotors in a set of power and flow modules. These bearings 103 can be of a type that receives lubrication from the process fluid.

The rotors can alternatively be non-rotatingly attached to a common rotor shaft which is stored to rotate in bearings arranged in a bearing housing (not shown).

Each rotor 101 comprises a set of rotor blades 104 which extend mainly in the radial direction from a rotor center axis C. In that case some of the rotor blades 104 have a permanent magnet 105 at the outer, peripheral end of the rotor blade. The permanent magnets 105 can be integrated into a ring element 106 which is connected to the rotor blades in the rotor circumference 107.

Rotor 101 is surrounded by an enclosure 108 which has connection means, such as flanges 109, for connection to adjacent power and flow modules 100. Seals, not shown in the drawings, are arranged as needed in the interfaces between the enclosures of the connected power - and the flow modules. Mounted in the housing 108 is a set of electromagnets with associated stator windings, marked in the drawings with the same reference number 110. The electromagnets 110 form an outer ring around the inner ring of permanent magnets, and the housing 108 can have the shape of a cylinder.

The rotor 101 is thus set in rotation by the permanent magnets moving in the magnetic field which is generated when current is supplied to the stator windings to activate the electromagnets.

To optimize operation, each power and flow module 100 in a set of power and flow modules can have an individual power supply and be separately controlled via dedicated frequency converters as illustrated by the VSD boxes in Figure 3.

If appropriate, the set of individually controlled power and flow modules may be arranged to include counter-rotating rotors, so that each clockwise rotating rotor is followed by a counter-clockwise rotating rotor, as illustrated by arrows R indicating the directions of rotation in Figure 3 .

The power and flow modules 100 can be arranged to follow directly after a preceding module without stator vanes being placed between the rotor vanes of successive modules 100.

Upon rotation, the power and flow module 100 generates an axial flow in the annular flow path that is formed through the motor's rotor which acts as a paddle wheel. The rotor blades 104 are designed with an angle of attack or angle of pitch oc to the flow F (see figure 3), and thus in relation to the central axis C. In a set of power and flow modules, at least one of the rotors can have blades with a different angle of attack than the other rotors in the set. The angle of attack can be changed successively from the first to the last rotor in the set.

The rotor blades 104 can be designed with an aero-foil to improve the operation in engine and power generation mode, respectively. As an illustration of this, the rotor blades can be designed with a convex-concave profile, and mounted with the concave side facing the direction of rotation as illustrated in the power and flow module 100'. A convex-concave rotor blade can alternatively be mounted with the convex side facing the direction of rotation as illustrated in the power and flow module 100''. In this way, the motor's rotor or impeller 101 can be designed to work optimally either in pressure increase mode, where energy is transferred to the fluid via the rotor blades, or in deceleration mode where energy is absorbed from the fluid via the rotor blades.

In practice, the pump may have to be designed as a compromise, and eventually lose some efficiency in one of its two operating modes. Due to its axial compactness, a result of stackable construction with no stationary guides inserted between the dynamic stages of the pump, overall length can still be kept within limits even if extra motor stages are added to compensate.

In deceleration mode, the power and flow module 100 works as a dynamo, inducing current in the stator windings from the rotating magnetic field produced by the permanent magnets, in rotation driven by the kinetic energy of the well fluid passing through the rotor.

A pressure regulation system is thus described, where pumps comprising the motor/generator unit can be arranged on wellheads and act to equalize the pressures in well fluid produced from wells on the seabed or produced from land-based hydrocarbon wells that produce with a different well fluid pressure. In this context, the pumps can be arranged on an installation module that can be connected to a wellhead or to an underwater or surface valve tree. However, the pumps can also be operated in other positions on the hydrocarbon production field, such as on downstream pipelines as the pumps can be operated for pressure equalization in fluid streams with different pressures in pipe connecting bridges/pipelines, manifolds, riser bases, PLEM or other pipelines installed on a subsea hydrocarbon production field.

The described pressure regulation system provides for the implementation of a method for pressure regulation which includes the following: - arrangement of a given pump in fluid communication with each well that receives fluid produced from this well and to deliver the fluid to downstream piping, each pump including a motor/generator- unit,

- and so that flow/pressure in delivered fluid is increased by operating the pump as a motor in power consumption mode, and so that flow/pressure in delivered fluid is reduced by operating the pump as a generator in power generation mode, as power recovered in power generation mode is divided and distributed between two or more pumps or sent to another recipient via a power distribution unit that is operationally connected to the pumps.

It has been explained above and illustrated in drawings of example designs, that a significant integrated, compact and energy-saving system for pressure regulation of well fluid produced from hydrocarbon wells can be achieved by implementing the principles presented here.

It is nevertheless obvious that modifications of the described embodiments are possible, without deviating from the scope and spirit of the invention as described above and defined in the attached patent claims.

Claims (16)

1. System designed for pressure regulation of well fluid produced from wells in a hydrocarbon production field, the system comprising: - a first pump (6) in fluid communication with a first well (W1-W5), and a second pump (6) in fluid communication with a second well (W1-W5), where the pumps are arranged to receive well fluid produced from the respective wells, and to deliver the fluid to downstream piping (P1-P5) or to equipment, - as the first and second pump each comprise a motor/generator unit (100, 100', 100'') which can be operated as a generator by the pump being driven by well fluid in power generation mode, and by the pump being driven in power consumption mode by operating the motor/generator unit as a motor, where the pumps are operationally connected via a power distribution unit (8) configured to distribute recovered energy between the pumps or other receivers. 2. Pressure regulation system according to claim 1, in that the pump (6) is a helico-axial pump which is adapted for increasing pressure in multiphase fluid. 3. Pressure regulation system according to claim 2, in that the pump (6) comprises a motor/generator unit where the motor is integrated in a power and flow module (100, 100', 100''). 4. Pressure regulation system according to claim 3, in that the power and flow module (100, 100', 100'') is an electrically driven flow machine with permanent magnets (105) mounted in the circumference of a rotor (101), while electromagnets and stator windings (110 ) is mounted on a casing (109) which encloses the rotor. 5. Pressure regulation system according to claim 4, in that the rotor in the power and flow module comprises rotor blades (104) which are given an angle of attack (a) against the direction of flow (F). 6. Pressure regulation system according to claim 5, in that the pump comprises a set of integrated power and flow modules arranged in sequence, in that each power and flow module (100, 100', 100'') is controlled individually via a dedicated frequency converter (9) . 7. Pressure regulation system according to claim 6, in that the set of power and flow modules in the pump comprises counter-rotating rotors (101) so that each rotor that rotates clockwise follows a rotor that rotates anti-clockwise. 8. Pressure regulation system according to claim 7, in that in a set of power and flow modules each module is arranged to follow directly after a preceding module without stationary guides inserted between the rotors in successive power and flow modules. 9. Pressure control system according to any one of claims 4-8, the rotor blades (104) being constructed so as to curve forwards or backwards in relation to the direction of rotation (R) of the rotor, for transferring energy to the well fluid, respectively for absorbing energy from the well fluid. 10. Pressure regulation system according to claim 9, in that in a set of stackable power and flow modules, the modules are alternately specified for transferring energy to the well fluid or for absorbing energy from the well fluid by corresponding design of the rotor blades (104). 11. Pressure regulation system according to any preceding claim, the power distribution unit (8) containing control logic which determines whether the pump shall operate in power consumption mode or in power generation mode. 12. Pressure regulation system according to claim 11, in that the current well fluid pressure is monitored and reported to the power distribution unit (8) from pressure sensors (11) which are arranged on well heads (5). 13. Pressure regulation system according to any preceding claim, in that the pumps are arranged on wellheads (5) and can be operated to equalize pressure in well fluid produced from wells (W1-W5) which produce with different well fluid pressures. 14. Pressure regulation system according to any preceding claim, the pumps being arranged on an installation module which can be connected to a wellhead, an underwater or surface valve tree. 15. Pressure control system according to any preceding claim, the pumps being arranged on downstream piping and operable to equalize pressure in fluid streams with different pressures in pipe connecting bridges, manifolds, riser bases, PLEM or other pipelines installed at a hydrocarbon production facility. 16. Method for controlling pressure in well fluid produced from wells (W1-W5) in a hydrocarbon production field, the method comprising: - arrangement of a pump (6) for each individual well and in fluid communication with this, to receive fluid produced from the relevant well and to deliver the fluid to downstream piping (P1-P5), each pump comprising a motor/generator unit (100, 100', 100"), - and that flow/pressure in the delivered fluid is increased by operating the pump as an engine in power consumption mode, and where flow/pressure in delivered fluid is reduced by operating the pump as a generator in power generation mode, with recovered power in power generation mode being distributed between the pumps or other receivers via a power distribution unit (8) which is operationally connected to the pumps.