NO324811B1 - underwater Pump - Google Patents

Abstract

The present invention relates to a pump unit comprising a pump with a pump shaft (13) in a pump housing for pumping a well fluid. A motor with a motor shaft (11) for operating the pump is located in the motor housing (1). At least one magnetic seal supports at least one of the shafts (11, 13) and at least one mechanical seal (5) seals around the at least one shaft (11, 13). A fluid connection (14) leads a fluid to the at least one mechanical seal (5). A method of preventing the intrusion of unconditioned well fluid into a sealing chamber is also described.

Description

The present invention relates to a subsea pump system for pressure increase in well fluid when pumping hydrocarbon fluids. More particularly, the invention relates to a pump with a liquid conditioning unit for conditioning a liquid fraction of a well stream. The conditioning unit conditions the fluid to make it suitable for use in mechanical bearings. The system is suitable, for example, for use in connection with magnetic bearings and high-speed motors.

The system has been specially developed for subsea compression stations.

An offshore gas field can be developed with installations located on the seabed that are connected to terminals on land or to an existing platform. The subsea installations comprise one or more production well frames where each well frame produces well fluids through manifold manifolds which are connected to one or more pipelines. The pipelines transport well fluids to an onshore terminal, an existing platform or any other receiving facility for further processing. Processed gas and condensate are exported to a 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 using reservoir pressure. Later in the production phase, or at the start of production, pressurization of the well fluid is prescribed to maintain the production level and to recover the projected gas and condensate volumes. This can be carried out by subsea compressors and pumping units.

Units for subsea fluid pressure increase for this purpose, with electric motors which prescribe a dry environment, and which use a pressurized gas-filled motor housing, appear for example from Norwegian patent no. 172075, NO 173197, Norwegian patent application no. 2001 5199 in addition to Norwegian patent application no. .2003 3034.

These publications demonstrate the application of gas-filled electric motors where the prevention of corrosion and other problems associated with the separation of hydrocarbon condensates and water in liquid form in the motor are considered.

NO 316236 shows a single-stage compressor with a radial impeller. The radial impeller is arranged directly on the drive shaft of an electric motor. In the method according to NO 316236, the gas required for lubrication of the sliding seals is taken from a turbo feeder, a pipeline or a gas storage. However, this Norwegian patent does not show a pump unit for pumping a well fluid with a pump housing and a pump shaft. There is also no indication of a magnetic bearing.

EP 1420167-A2 also shows a device for circulating sealing gas for mechanical dry seals in a centrifugal compressor. The patent application does not mention a pump. Consequently, a pump for pumping a well fluid with a pump housing and a pump shaft is not described either. The application also does not show a motor with a motor shaft for operating a pump, where the motor is located in a house. Nor does a magnetic bearing appear.

GB 1289442 discloses a device for sealing the drive shaft of a centrifugal pump. The pump is installed in a pressure vessel. The pump is driven by a motor via a shaft which is sealed with three seals (packers 8, 9, 12). However, the use of a magnetic bearing or a mechanical seal for sealing around the motor's or pump's shaft where this contains a fluid connection for guiding fluid to the mechanical seal does not appear.

US 3508758 describes a fluid seal for a rotating shaft. The seal is a mechanical seal that is supplied with a fluid.

Norwegian patent application 2003 3034 describes a gas compressor module with a pressure housing. The module comprises an electric motor and a compressor connected to at least one shaft. The shaft is stored in magnetic bearings. The application describes volume and pressure control of the gas flowing into the engine, and the use of a supply of dry hydrocarbon gas. Furthermore, means are described for sensing the pressure in the inlet and outlet whereby, based on the measured pressures, the pressure and volume regulator controls the pressure for injecting gas from the supply into the engine housing.

However, the application does not describe how to accommodate and solve the problem of the requirement for high speed for a high-pressure multi-stage pump unit.

According to one embodiment of the invention, the need for a lubricating oil is removed as the unit can use magnetic bearings and the use of a gearbox or transmission which is traditionally lubricated with oil, and which consequently potentially leaks, is bypassed by using a high speed motor. This reduction of moving components by bypassing a gearbox also reduces the number of parts that can fail.

This is achieved with the system according to the present invention and which defines a pump unit comprising a pump with a pump shaft, in a pump housing for pumping a well fluid. A motor with a motor shaft is adapted to drive the pump. The engine is housed in an engine housing. At least one magnetic bearing for storage of at least one of the shafts and in this case the magnetic bearing is one of several bearings. However, in many cases the main bearings in the unit will be magnetic bearings to fully utilize the advantages of this type of bearing. At least one magnetic seal, in some cases located in a seal chamber, seals around at least one of the shafts. The sealing chamber can be used to transfer the sealing fluid to the seal. A fluid connection can lead fluid to the seal chamber or directly to the mechanical seal.

The pump may further comprise at least one conditioning unit connected to an outlet or an intermediate stage of the pump for removing contaminants in at least one proportion of the well fluid. The pressure can be taken from a source that supplies a suitable pressure to avoid a pressure regulator. A fluid connection may be provided between the seal or seal chamber and the conditioning unit, adapted to convey conditioned well fluid from the conditioning unit to the seal.

The motor can be a high speed motor with direct drive of the pump to avoid the use of a gearbox.

The conditioning unit may comprise at least one hydrocyclone with particle removal properties, and a fluid connection between the at least one hydrocyclone and the inlet side of the pump, for guiding the removed particles to the inlet side of the pump. However, several hydrocyclones may be required to achieve sufficient capacity and purification.

A method for preventing the ingress of unconditioned well fluid into at least one seal or a seal chamber in a pump for pumping unconditioned well fluid may comprise leading a well fluid from the well to a pump, pumping the well fluid with the pump, leading a fraction of the well fluid from an outlet or intermediate stage of the pump to a conditioning unit, conditioning the well fluid with the conditioning unit to remove contaminants in the well fluid, and directing the well fluid from the conditioning unit to the at least one mechanical seal to displace contaminated well fluid from the seal.

The invention may include a high-speed engine which may be gas- or fluid-filled.

A mechanical seal of the appropriate type can separate the motor and pump, and can be flushed with the conditioned well fluid.

A mechanical seal is typically a unit comprising one or more chambers with a blocking or sealing element formed by a rotating ring and a stationary ring (labyrinth seal). If the engine is a gas-filled engine, the seals can seal the engine to prevent ingress of the fluid surrounding the engine.

To maintain cooling of the surfaces between the rings, either a separate liquid such as TEG, oil etc. or a medium from the pump can be used. If this medium contains contaminants and impurities, it must be conditioned to avoid unnecessary wear. The well fluid can cause significant erosion and rapid degradation of the seals, shafts and bearings.

The high-speed motor in this context can be a motor that runs faster than a two-pole motor at a mains input frequency, i.e. above 3600 rpm at 60 Hz and 3000 rpm at 50 Hz.

A subsea compressor station where this system may be included may include the following modules and parts:

one or more compression lines and pump modules,

one or more current-breaking modules,

inlet and outlet manifolds,

inlet coolers (if the supply pipelines are not sufficient for cooling the well stream),

inlet sand trap (for random sand production),

parking ring for main transformer and power umbilical connection, head,

process system,

management system.

The pump driveline may include:

pump module,

a drive unit for variable pump speed (VSD), (variable speed drive), remotely controlled and manually operated valves,

connecting piping,

control system comprising control modules.

The pump can be driven directly by a high-speed motor. The electric motor can be cooled with a hydrocarbon gas or a fluid. The system can use magnetic radial and axial bearings for each of the subsea pump modules, in addition to run-down bearings.

The pumping system can be designed to handle continuous fine particle/sand production. The rotating equipment can be protected against wear and degradation from solids to ensure high efficiency, long life and reliability.

The conditioning unit separates solids from the liquid, which in turn is fed to the sealing chambers.

The pumping station may have connections for well fluid outlets, and may also include ROV-operated valves for guiding the well fluids to the various pipelines.

The well fluids from the connecting production well frames can be distributed to a separator equipped with remotely activated isolation valves in the inlet pipe. Most of the solids from production can be removed in separators. Sand/fine particles/solids that enter the pump station can be separated in the separators and transported via the liquid pump to the discharge pipeline. However, a sand trap for incidental sand production can be used to remove sand from the inlet well fluid.

Brief description of the attached drawing:

Fig. 1 is a schematic representation of a subsea pump module according to an embodiment of the invention.

Detailed description of embodiments of the invention with reference to the attached drawing: Figure 1 shows a subsea pump module according to an embodiment of the invention. The pump module comprises a pressure chamber 1 for an electric motor, a connecting or intermediate chamber 2, and a pressure chamber 4 for a pump. The motor in the pressure chamber 1 is connected to the pump in the pressure chamber 4 with a coupling 3 in the coupling chamber 2. Alternatively, the motor and the pump can be connected to the same shaft. The coupling 3 may for example be a flange or any other suitable connection. Alternatively, the coupling chamber 2 may comprise a transmission if a certain turnover ratio is required between the motor and the pump. However, the motor may be a high-speed motor so that there is no need for a gearbox.

The shaft 11 of the motor is stored in the bearing 12, in some cases placed in a bearing chamber, and the pump shaft 13 is stored in these bearings 12. The shafts can typically carry rotors. The bearings can be magnetic bearings.

An outlet conditioning unit 8 receives a flow from an outlet 7 on the pump and supplies a conditioned fluid to the mechanical seals 5, in some cases located in the seal chambers. As mentioned, the sealing chambers can be sealed with mechanical seals. Alternatively, the mechanical seals that are in some cases placed in the seal chambers can be supplied with oil or TEG from a separate source. In this case, the conditioning unit 8 is bypassed. The pump can be a multistage pump, and the liquid for the conditioning unit 8 can be taken from an intermediate stage of the pump. A line 14 from the conditioning unit 8 supplies liquid from the conditioning unit 8 into the pump's mechanical seals 5.

The pump delivers a compressed outlet fluid through line 7.

The pump has an inlet line 6.

The pressure chamber 1 which houses the motor includes electrical connections 10. The bearing chambers can be sealed from liquid so that sealed bearings do not necessarily have to be used. The bearing chambers may include connections for bearing coils for the magnetic bearings and sensors.

The conditioning unit 8 can typically comprise one or more hydrocyclones with devices for removing particles, for example sand etc. The removed particles can be returned to the suction side of the pump to be brought further into the flow of the well fluid.

Fluid that leaks out of the seals can be returned to the suction side of the pump.

The pump is typically used to pressurize a well fluid to a certain pressure.

The pump is typically a multi-stage pump.

Claims (5)

1. A pump unit comprising a pump with a pump shaft (13), in a pump housing (4) for pumping a well fluid; a motor with a motor shaft (11) for operating the pump, in a motor housing (1), characterized by at least one magnetic bearing (12) for storing at least one of the shafts (11,13); at least one mechanical seal (5) for sealing around at least one of the shafts (11, 13); and a fluid connection (14) for leading a fluid to the at least one mechanical seal (5) from at least one conditioning unit (8). 2. Pump unit according to claim 1, characterized in that the at least one conditioning unit (8) is connected to an outlet (7) or an intermediate step of the pump for removing contaminants in at least part of the well fluid; and the fluid connection (14) between the mechanical seal (5) and the conditioning unit (8) is adapted to convey conditioned well fluid from the conditioning unit (8) to the mechanical seal (5). 3. Pump unit according to claim 1 or 2, characterized in that the motor is a high-speed motor with direct operation of the pump. 4. Pump unit according to claim 2, characterized in that the conditioning unit (8) comprises at least one hydrocyclone with a particle removal feature; a fluid connection (16) between the at least one hydrocyclone and the inlet side of the pump, for guiding the removed particles to the inlet side of the pump for removal. 5. Procedure for preventing penetration of unconditioned well fluid into at least one mechanical seal (5) in a pump for pumping unconditioned well fluid, characterized in that it comprises: guiding a well fluid from a well to a pump; pumping the well fluid with the pump; directing a portion of the well fluid from an outlet (7) or an intermediate stage of the pump to a conditioning unit (8); conditioning the well fluid with the conditioning unit to remove contaminants in the well fluid; and guiding the well fluid from the conditioning unit (8) to the at least one mechanical seal to displace contaminated well fluid from the seal (5).