GB2450565A

GB2450565A - Pressure boosting apparatus with jet pump, mechanical pump and separator

Info

Publication number: GB2450565A
Application number: GB0713626A
Authority: GB
Inventors: Mirza Najam Ali Beg; Mir Mahmood Sarshar
Original assignee: Caltec Ltd
Current assignee: Caltec Ltd
Priority date: 2007-06-29
Filing date: 2007-07-13
Publication date: 2008-12-31
Also published as: GB0712643D0; GB0713626D0

Abstract

Apparatus for boosting the pressure of flowing fluids, especially in oil and gas wells, includes a jet pump 24 having a low pressure, LP, inlet 35 for LP fluid, a high pressure, HP, inlet 22 for HP liquid and a medium pressure, MP, outlet 36 for MP fluid. An MP separator 38 has inlet 40 receiving MP fluid from the jet pump outlet, an MP gas outlet 42 and an MP liquid outlet 44. A liquid return line 52 connects the MP separator liquid outlet and the HP jet pump inlet for returning at least some of the MP separated liquid to the jet pump, and a mechanical pump 58 is connected into the liquid return line 52 for boosting the pressure of the returned liquid. Multiphase fluid may be supplied to an LP separator 4 with LP liquid feeding the boost pump and LP gas supplied to the jet pump LP inlet. Re-use of the liquid means that the liquid quantity available for motive flow is greater than that entering the system.

Description

PRESSURE BOOSTING APPARATUS

The present invention relates to an apparatus for boosting the pressure of flowing fluids, and in particular but not exclusively for boosting the production of oil and gas wells. The invention also relates to a method of increasing the pressure of flowing fluids.

In order to increase or maintain the production from oil fields with a low production well head pressure (PWHP), a boosting system may be required. Such a system allows the pressure of the extracted gases and liquids to be boosted to the pressure required by downstream processing systems or for transportation by pipeline. If the pressure of these fluids cannot be boosted efficiently, it may be uneconomic to maintain production, orin the case of the multiphase fluids, it may be necessary to flare (burn off) the low pressure gas after separating it from the liquid phase.

In some situations it is known to separate multiphase fluids and use a mechanical booster pump to boost the pressure of the liquid phase, while a gas compressor is used to boost the pressure of the gas phase. However, gas compressors are very large and expensive pieces of equipment and this solution may not be viable where space is at a premium (for example :.:: on offshore oil production platforms) or where the available resources do not justify the necessary investment. * I.

It is also known to use jet pumps (eductors) to boost the production of oil and gas wells. ***

Jet pumps are simple, reliable, low cost devices that use fluids from a high pressure source : *20 to boost the pressure of fluids from a low pressure source. The high pressure fluids may for *: *: example be obtained from nearby high pressure wells, or from other available sources such as high pressure gas from a gas compressor or high pressure water used for injection into oil or gas wells to maintain reservoir pressure. Such systems work well, provided that a suitable high pressure fluid source is available.

An example of a system for boosting pressure that uses jet pumps is described in EPO7 1781 8A. This system uses fluids from high pressure wells to boost the production of adjacent low pressure wells.

EP1606492A describes another system, in which the gas and liquid phases of a low pressure fluid are separated, and high pressure gas from any available source (e.g. from a high pressure well, a lift gas supply or a compressor) is used to boost the low pressure gas phase using ajet pump, while a mechanical pump is used to boost the pressure of the liquid phase.

There are however a number of problems with the use of available HP motive fluids for jet pump systems. For example, a suitable high pressure fluid supply that can be used as the motive flow in a jet pump may be unavailable, or may be of inadequate pressure or flow rate. The high pressure fluid may not be sustainable in the long term, for example if it is drawn from another well. If high pressure water is used, the downstream processing system may not have sufficient capacity to cope with the additional fluid quantity. Furthermore, the addition of a motive fluid to the fluids produced from the well will increase the total quantity of fluid flowing through the transportation pipeline, leading to an increased pressure loss along the pipeline and thereby diminishing or negating the benefits gained by using a pressure boosting system.

It is an object of the present invention to provide a pressure boosting system that mitigates at least some of the aforesaid disadvantages. Another preferred object is to provide a pressure boosting system for use in oil and gas production that reduces the back pressure * :* on low pressure wells and delivers the produced gas and liquid phases at a higher pressure, * :* : :* as dictated by downstream processing and production requirements.

According to one aspect of the present invention there is provided an apparatus for boosting the pressure of flowing fluids, the apparatus including a jet pump having a low pressure (LP) inlet for LP fluid, a high pressure (HP) inlet for HP liquid and a medium pressure (MP) outlet for MP fluid, a MP separator device having an inlet connected to receive the MP fluid from the outlet of the jet pump, a MP gas outlet for separated MP gas and a MP liquid outlet for separated MP liquid, a liquid return line connected to the MP liquid outlet of the separator and the HP inlet of the jet pump for returning at least some of the separated MP liquid from the separator device to the HP inlet of the jet pump, and a mechanical pump connected into the liquid return line for boosting the pressure of the liquid delivered to the HP inlet of the jet pump.

The terms "low pressure", "medium pressure" and "high pressure" are all used in a relative sense and are not intended to indicate absolute pressure values. A "low pressure" is therefore lower than a "medium pressure", which is lower than a "high pressure". The term "fluid" encompasses liquids, gases and multiphase fluids (mixtures of gas and liquid).

The system makes it possible to boost or maintain production from low pressure wells. It can be used to increase the pressure of the produced fluids to that required by downstream processing systems or for transportation by pipeline. It is therefore possible to make use of low pressure produced gas rather than flaring it. It does not need a complex and expensive gas compressor and unlike previous jet pump systems it does not require an external source of high pressure fluid (e.g. lift gas, fluids from HP wells or HP water) to drive the jet pump. Furthermore, as no extra fluids are added to the produced fluids, it does not increase in the flow rate through the delivery pipeline and does not cause an increase in the pressure differential along the pipeline. There is also no additional burden on downstream processing systems. The production boosting system is cost effective, simple and reliable and has low maintenance requirements.

Advantageously, the apparatus includes a LP separator device having an inlet connected to :. receive LP multiphase fluid, a LP gas outlet for separated LP gas and a LP liquid outlet for *::::* separated LP liquid, wherein the LP inlet of the jet pump is connected to receive LP gas * from the LP gas outlet of the LP separator device. Providing a LP separator to separate the : LP gas and liquid at the start of the process ensures highly efficient operation, as it allows the liquid to be used as the motive flow for driving the gas in the jet pump.

: . Advantageously, the LP liquid outlet of the LP separator is connected to the liquid return :: line to deliver the LP liquid into the liquid return line upstream of the mechanical pump.

Advantageously, the apparatus includes a level sensor connected to the sense the level of LP liquid in the LP separator, and a LP liquid valve for controlling the flow of LP liquid through the LP liquid outlet of the LP separator, wherein the LP liquid valve is constructed and arranged to be controlled according to the sensed level of the LP liquid in the LP separator.

Advantageously the apparatus includes a LP gas pressure transducer connected to the sense the pressure of the LP gas at the LP gas outlet of the LP separator, and a LP gas valve for controlling the pressure of the LP separator, wherein the LP gas valve is constructed and arranged to be controlled according to the sensed pressure of the LP gas at the LP gas outlet of the LP separator.

Alternatively, the LP inlet of thejet pump may be connected to receive LP multiphase fluid.

This arrangement is simpler than the arrangement in which the LP gas and liquid are first separated, but it is not so efficient.

Advantageously, the MP liquid outlet of the MP separator is connected to a MP liquid outlet line.

Advantageously, the apparatus includes a level sensor connected to the sense the level of MP liquid in the MP separator, and a MP liquid valve for controlling the flow of MP liquid through the MP liquid outlet line, wherein the MP liquid valve is constructed and arranged to be controlled according to the sensed level of the MP liquid in the MP separator.

Advantageously, the apparatus includes a MP gas pressure transducer connected to the sense the pressure of the MP gas at the MP gas outlet of the MP separator, and a MP gas valve for controlling the flow of MP gas through the MP gas outlet of the MP separator, wherein the MP gas valve is constructed and arranged to be controlled according to the I...

sensed pressure of the MP gas at the MP gas outlet of the MP separator.

* Advantageously, the apparatus includes a HP liquid pressure transducer connected to the I..

sense the pressure of the HP liquid at the HP inlet of the jet pump, and a MP liquid return >5 valve for controlling the flow of MP liquid through the liquid return line, wherein the MP : liquid return valve is constructed and arranged to be controlled according to the sensed pressure of the HP liquid at the HP inlet of the jet pump.

Advantageously, the apparatus includes a cooler device for cooling MP liquid flowing through the liquid return line.

Advantageously, the apparatus includes a gas outlet line for separated MP gas and a liquid outlet line for separated MP liquid.

Alternatively, the apparatus may include a co-mingling device having a gas inlet connected to receive separated MP gas, a liquid inlet connected to receive separated MP liquid, and a multiphase outlet line for the combined MP fluid.

According to another aspect of the present invention there is provided method of boosting the pressure of flowing fluids, the method including delivering LP fluid to a LP inlet of a jet pump, delivering HP liquid to a HP inlet of the jet pump, combining the LP fluid with the HP liquid in the jet pump to form MP fluid, delivering the MP fluid from a MP outlet of the jet pump to a MP separator device, drawing separated MP gas from a MP gas outlet of the MP separator, drawing separated MP liquid from a MP liquid outlet of the MP separator, boosting the pressure of at least some of the separated MP liquid with a mechanical pump, and returning the pressure boosted liquid to the HP inlet of the jet pump.

Advantageously, the method includes receiving LP multiphase fluid, delivering the LP multiphase fluid to a LP separator, separating the LP multiphase fluid to form LP gas and LP liquid, delivering the separated LP gas to the LP inlet of the jet pump, combining the separated LP liquid with at least some of the separated MP liquid, boosting the pressure of the combined liquid with a mechanical pump, and returning the pressure boosted liquid to the HP inlet of the jet pump. * e*. * S

Advantageously, the method includes sensing the level of LP liquid in the LP separator, and * ** * .... controlling the flow of LP liquid through the LP liquid outlet of the LP separator according to the sensed level.

r >s Advantageously, the method includes sensing the pressure of the LP gas at an LP gas outlet : of the LP separator, and controlling the flow of LP gas through the LP gas outlet according to the sensed pressure.

Alternatively, the method may include receiving LP multiphase fluid and delivering the LP multiphase fluid to the LP inlet of the jet pump.

Advantageously, the method includes sensing the level of MP liquid in the MP separator, and controlling the flow of MP liquid through a MP liquid outlet line according to the sensed MP liquid level.

Advantageously, the method includes sensing the pressure of the MP gas at the MP gas outlet of the MP separator, and controlling the flow of MP gas through the MP gas outlet according to the sensed MP gas pressure.

Advantageously, the method includes sensing the pressure of the HP liquid at the HP inlet of the jet pump, and controlling the flow of MP liquid returned to the HP inlet of the jet pump according to the sensed HP liquid pressure.

Advantageously, the method includes cooling the MP liquid returned to the HP inlet of the jet pump.

Advantageously, the method includes co-mingling the separated MP gas with at least at least some of the separated MP liquid, and delivering the combined MP multiphase fluid through an outlet. Alternatively, the separated MP gas and the separated MP liquid may be delivered to separate outlets.

Certain embodiments of the inventions will now be described by way of example with reference to the accompanying drawings, in which: S. . Figure 1 is a schematic diagram illustrating a pressure boosting system according to a first embodiment of the invention, and * S. Figure 2 is a schematic diagram illustrating a pressure boosting system according to a S..

* second embodiment of the invention.

:. The system shown in Figure 1 includes a low pressure (LP) inlet line 2 for LP multiphase 2s fluids (gases and liquids). The LP inlet line 2 is connected to the inlet of a LP gas-liquid separator 4. The LP gas-liquid separator 4 may for example be a conventional knock out vessel, comprising a cylindrical vessel with a vertical axis, having a tangential inlet port in one side, a gas outlet port 6 at its upper end and a liquid outlet port 8 at its lower end.

In use, low pressure multiphase fluids from the LP inlet line 2 are introduced into the LP gas-liquid separator 4, where they separate under gravity and cyclonic action. A body of liquid collects in the lower part 10 of the vessel, while the gas rises into the upper part 12 of the vessel. The separated LP liquid exits through the liquid outlet port 8 while the LP gas exits through the gas outlet port 6.

The liquid outlet port 8 feeds through a LP liquid outlet line 14 and a flow control valve 16 to the inlet of a mechanical booster pump 18. Operation of the flow control valve 16 is controlled by a level-sensing device 19 that is attached to the LP gas-liquid separator 4 and is designed to maintain a constant liquid level in the vessel. The booster pump 18 may be any kind pump that acts mechanically rather than pneumatically: preferably it is a positive displacement pump. The booster pump 18 increases the pressure of the liquid and delivers the resulting high pressure (HP) liquid through a one-way valve 20 to the high pressure inlet 22 of ajet pump 24. A pressure transducer 26 monitors the pressure at the inlet of the jet pump 24. The high pressure liquid serves as the motive flow for the jet pump 24.

The LP gas flowing through the gas outlet port 6 enters a gas outlet line 28. The pressure of the gas is controlled by a gas outlet valve 30, operation of the valve 30 being controlled by a second pressure transducer 32 connected to the gas outlet port 6 so as to maintain a constant pressure in the LP separator 12.

n... The LP gas in the gas outlet line 28 is fed through a non-return valve 34 into the low .... pressure inlet 35 of the jet pump 24. Thejet pump 24 is driven by the high pressure liquid * :* : : from the booster pump 18, which serves as the motive flow for the jet pump. The jet pump 24 combines the LP gas with the HP liquid and increases the pressure of the combined fluids to a medium pressure (MP) that is below the pressure of the HP liquid driving the jet * ,* pump, but higher than the original pressure of the LP fluids flowing through the inlet line * *** *** * * The outlet 36 of the jet pump 24 is connected to the inlet of aMP gas-liquid separator 38.

The MP gas-liquid separator 38 may also be a conventional knock out vessel, comprising a cylindrical vessel with a vertical axis, having a tangential inlet 40, a gas outlet port 42 at its upper end and a liquid outlet port 44 at its lower end.

In use, the combined MP multiphase fluids from the jet pump 24 are introduced into the MP gas-liquid separator 38, where they separate under cyclonic action and gravity. A body of liquid collects in the lower part 46 of the vessel, while the gas rises into the upper part 48 of the vessel. The MP liquid then exits through the liquid outlet port 44 while the MP gas exits through the gas outlet port 42.

The liquid outlet port 44 feeds into a liquid outlet line 50 and a liquid return line 52, the flow of MP liquid into each of these lines being controlled by a liquid outlet valve 54 and a liquid return valve 56, respectively. A cooler 58 is provided in the liquid return line 52 for cooling the MP liquid, should this be necessary.

The pressure of the MP liquid flowing through the liquid return line 52 may if required be reduced by the liquid return valve 56 to approximately the pressure of the LP liquid flowing from the liquid outlet 8 of the LP gas-liquid separator 4. Those LP liquids are then combined and fed to the inlet of the mechanical booster pump 18, which increases the pressure of the combined liquid and delivers it to the high pressure inlet 22 of the jet pump 24, as described above. The booster pump 18 may have a variable speed feature to assist with start-up and provide a build up in the liquid flow rate entering the pump.

The flow of MP liquid through the liquid outlet line 50 is controlled by the liquid outlet valve 54. Operation of the liquid outlet valve 54 is controlled by a level-sensing device 60 attached to the MP gas-liquid separator vessel 38, which is designed to maintain a constant liquid level in the vessel.

The MP gas flowing through the gas outlet port 42 enters a gas outlet line 62. The rate of flow through the gas outlet line 62 is controlled by a gas outlet valve 64, operation of the *.25 gas outlet valve 64 being controlled by a third pressure transducer 66, which is connected * to the gas outlet port 42 and arranged to maintain a constant pressure in the MP separator ****** 38.

The MP gas flowing through the gas outlet line 62 and the MP liquid flowing through the liquid outlet line 50 may leave the system separately through those two outlet lines.

Alternatively, both MP fluids may be fed to a co-mingling device 68 through respective gas and liquid feed lines 70,72 and isolation valves 74,76. The MP fluids are combined in the co-mingling device 68 and the resulting combined MP multiphase fluid then leaves the system through a MP multiphase outlet line 78.

Because the liquid phase is recycled continuously via the MP gas-liquid separator 38 and the liquid return line 52, the total amount of liquid fed to the HP inlet 22 of the jet pump 24 may be several times the amount of liquid phase contained within the multiphase fluids flowing into the system through inlet line 2 from LP wells. The total flow rate of the liquid phase fed to the jet pump as the motive flow can typically range between three and five times the flow rate of the liquid phase from the LP wells linked to the system, although this is not a limit for the system. The quantity of liquid that is available for use as the motive flow is therefore substantially increased as compared to a system in which the jet pump is driven only by fluids entering system. This allows it to boost the pressure of both the gas and liquid phases, rather than just the liquid phase. The jet pump can operate efficiently to increase the pressure of the gas phase, allowing it to be transported or processed rather than simply flared off, even if the proportion of gas within the LP multiphase fluids entering the system is relatively high.

The operation of the system and its key components is controlled by the following control components: * the liquid level of the LP separator 4, which is controlled by the level detection *:::* system 19 and the control valve 16, * the operating pressure of the LP separator 4, which is controlled by the pressure transducer 32 and the control valve 30, 1 ** * * * * . * the operating pressure of the second separator 38, which is controlled by the * pressure transducer 66 and the control valve 64, * the liquid level of the second separator 38, which is controlled by the level detection system 60 and the control valve 54, * the flow rate of liquid re-circulated through liquid return line 52, which is controlled by the pressure transducer 26 and the control valve 56.

The build-up of re-circulated liquid flowing through liquid return line 52 is achieved gradually at start-up under a semi-manual procedure and continues until the pressure transducer 26 at the HP inlet to the jet pump 24 reads the required operating value. The characteristics of the jet pump 24 are such that when the pressure at the outlet of the mechanical booster pump 18 reaches a specified value then the desired total HP liquid flow rate needed by the jet pump is reached.

Under certain circumstances, the re-circulation of liquid through the pumping system may result in the heating of the liquid phase. For this reason a cooler system 58 is installed on liquid return line 52 to maintain the temperature at a desired value.

The boosted MP gas and liquid phases in outlet lines 62,50 may flow independently along the two lines. Alternatively, in applications when there is only one line available for transport or export of the produced fluids the boosted gas and liquid phases can be combined through the co-mingling device 68 and the mixture will then flow through the single multiphase outlet line 78.

The system enables the back pressure on LP wells to be reduced, thus increasing their production. The boosting system boosts the pressure of the produced fluids to that required *. by the downstream production system or for export through lines 50, 62 or 78.

*.. The drop in the back pressure (dP) on LP wells may be only a few bar (typically 2 to 5 bar) or may be higher if required. The delivery pressure of the booster pump 58 is dictated by the amount of LP gas to be handled as the LP flow by the jet pump 24 and the dP or level : 25 of pressure boost required to be achieved by the jet pump.

****** * Typically, the pressure ratio between the HP liquid at the HP inlet of the jet pump 24 measured by the transducer 26 and the LP gas at the gas outlet of the LP separator 4 measured by the transducer 32 will be in the range 3 to 30, or may be higher depending on the level of boost desired for the produced fluids. The typical level of pressure boost achieved by the jet pump 24 is generally defined by the ratio of the discharge pressure of the jet pump (Pd) and the LP inlet pressure measured by transducer 32. This ratio may typically range from as little as 1.2 to as high as 4.0.

As the HP liquid phase is the motive flow that boosts the pressure of the LP gas, the volumetric flow rate of the LP gas phase could be in the order of two to ten times the volumetric flow rate of the HP liquid phase at the operating pressure and temperature.

These ratios are not the limit of the system and are quoted only as typical values.

The values set out above depend on the desired ratio of the delivery pressure as measured at transducer 66 to the inlet gas pressure measured at transducer 32. Use of the system is particularly attractive when the gas/oil ratio (GOR) of the LP inlet fluid is relatively low.

The GOR is normally defined as standard cubic feet of gas per barrel of oil produced (Scf/bbl) and typical values for low GOR are below 600 Scffbbl, although this not a limit for the system. Naturally, the lower the GOR, the lower will be both the amount of the motive liquid required for the jet pump 24 and also the power rating of the booster pump 18.

The main benefit of this system is the elimination of any need to flare the LP gas, or use a compressor to boost the pressure of the LP gas. It is worth noting that if a compressor were used for boosting the pressure of the LP gas, a bulky knock-out vessel would then be needed to remove excess mist in the separated gas and ensure that the compressor receives * gas free of any contaminant J iquid droplets. The need for the knock-out vessel, the cost of * ** the compressor and the maintenance requirements of the compressor make the use of a * compressor far less attractive, compared with the system described herein involving the use S..

ofajet pump, which is of much lower cost and is simple to operate. ** *.

* The system shown in Figure 2 includes an inlet line 102 for low pressure multiphase fluids S..... - * (gas and liquid), which are fed through a non-return valve 104 into the low pressure inlet ofajetpump 106. Theoutlet 108 ofthejetpump 106 isconnectedtothe inletofaMP gas-liquid separator 110. The gas-liquid separator 110 may for example be a conventional knock out vessel, comprising a cylindrical vessel with a vertical axis, having a gas outlet port 112 at its upper end and a liquid outlet port 114 at its lower end.

In use, MP multiphase fluids from the jet pump 106 are introduced into the MP gas-liquid separator 110, where they separate under gravity or a combination of cyclonic action and gravity. A body of liquid therefore collects in the lower part 116 of the vessel, while the gas rises into the upper part 118 of the vessel. The MP liquid then exits through the liquid outlet port 114 while the MP gas exits through the gas outlet port 112.

The liquid outlet port 114 feeds into a liquid outlet line 120 and a liquid return line 122, the flow of liquid through each of the lines being controlled respectively by a liquid outlet valve 124 and a liquid return valve 126. A cooler 127 is provided in the liquid return line 122 for cooling the liquid, should this be necessary.

Liquid flowing through the liquid return line 122 is fed to the inlet of a mechanical booster pump 128, which increases the pressure of the liquid and delivers the resulting high pressure liquid to the high pressure inlet 130 of the jet pump 106, through a one-way valve 132. A pressure transducer 134 monitors the pressure at the inlet of the jet pump 106. The high pressure liquid serves as the motive flow for the jet pump 106, which increases the pressure of the low pressure multiphase fluids flowing into the jet pump through the low pressure inlet line 102.

The MP gas flowing through the gas outlet port 112 enters a gas outlet line 136, the pressure of gas at the gas outlet port 112 being controlled by a gas outlet valve 138. The gas outlet valve 138 is in turn controlled by a second pressure transducer 140 connected to * the gas outlet port 112, which operates to maintain a constant pressure in the separator 110. * **

* Operation of the liquid outlet valve 124 is controlled by a level-sensing device 142 attached I..

to the gas liquid separator vessel 110, which is designed to maintain a constant liquid level " *5 in the vessel. *

****** * In one embodiment, gas in the gas outlet line 136 flows through an isolation valve 144 and a gas feed line 146 into a co-mingling device 148, where it is combined with the liquid flowing through the liquid outlet line 120. The combined multiphase fluid then leaves through a MP outlet line 150.

Alternatively, instead of re-combining the medium pressure gas and liquid, the gas and liquid can leave through separate medium pressure gas and liquid outlet lines 152, 150.

The second system shown in Figure 2 is therefore similar to the first system shown in Figure 1, except that the LP gas-liquid separator is omitted and the combined LP multiphase fluid flowing through the inlet line 102 is fed directly to the LP inlet 105 of the jet pump 106. This system operates in essentially the same manner as the first system described above. The main difference is that the jet pump 106 receives the combined LP gas and liquid phases without any separation of those phases.

Feeding the total LP multiphase fluids to the jet pump 106 requires that the amount of HP liquid phase supplied to the jet pump as the motive flow is increased. This system may also require a higher pressure for the HP motive liquid phase generated by the booster pump 128. In this case, the flow rate of re-circulated liquid phase passing through the liquid return line 122 may typically be increased to between two and four times the flow rate of LP liquid produced from LP wells. The advantages provided by the simpler arrangement of the second system are therefore offset to some extent by the added power required by the booster pump 128 and theadditional liquid flow rate that the booster pump 128 and the jet pump 106 must be able to handle. * 20 * * S... * .. * S * * *. S..

I S. ** * S S * .

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S.....

S

Claims

1. An apparatus for boosting the pressure of flowing fluids, the apparatus including ajet pump having a LP inlet for LP fluid, a HP inlet for HP liquid and a MP outlet for MP fluid, a MP separator device having an inlet connected to receive the MP fluid from the outlet of the jet pump, a MP gas outlet for separated MP gas and a MP liquid outlet for separated MP liquid, a liquid return line connected to the MP liquid outlet of the separator and the HP inlet of the jet pump for returning at least some of the separated MP liquid from the separator device to the HP inlet of the jet pump, and a mechanical pump connected into the liquid return line for boosting the pressure of the liquid delivered to the HP inlet of the jet pump.

2. An apparatus according to claim I, including a LP separator device having an inlet connected to receive LP multiphase fluid, a LP gas outlet for separated LP gas and a LP liquid outlet for separated LP liquid, wherein the LP inlet of the jet pump is connected to receive LP gas from the LP gas outlet of the LP separator device.

3. An apparatus according to claim 2, wherein the LP liquid outlet is connected to the :. liquid return line to deliver the LP liquid into the liquid return line upstream of the :..::: mechanical pump.

* **

4. An apparatus according to claim 2 or claim 3, including a level sensor connected to the sense the level of LP liquid in the LP separator, and a LP liquid valve for S..

controlling the flow of LP liquid through the LP liquid outlet of the LP separator, wherein the LP liquid valve is constructed and arranged to be controlled according to the sensed level of the LP liquid in the LP separator.

5. An apparatus according to claim 2, 3 or 4, including a LP gas pressure transducer connected to the sense the pressure of the LP gas at the LP gas outlet of the LP separator, and a LP gas valve for controlling the pressure of the LP separator, wherein the LP gas valve is constructed and arranged to be controlled according to the sensed pressure of the LP gas at the LP gas outlet of the LP separator.

6. An apparatus according to claim 1, wherein the LP inlet of the jet pump is connected to receive LP multiphase fluid.

7. An apparatus according to any preceding claim, wherein the MP liquid outlet of the MP separator is connected to a MP liquid outlet line.

8. An apparatus according to claim 7, including a level sensor connected to the sense the level of MP liquid in the MP separator, and a MP liquid valve for controlling the flow of MP liquid through the MP liquid outlet line, wherein the MP liquid valve is constructed and arranged to be controlled according to the sensed level of the MP liquid in the MP separator.

9. An apparatus according to any preceding claim, including a MP gas pressure transducer connected to the sense the pressure of the MP gas at the MP gas outlet of the MP separator, and a MP gas valve for controlling the flow ofMP gas through the MP gas outlet of the MP separator, wherein the MP gas valve is constructed and arranged to be controlled according to the sensed pressure of the MP gas at the MP gas outlet of the MP separator.

10. An apparatus according to any preceding claim, including a HP liquid pressure transducer connected to the sense the pressure of the HP liquid at the HP inlet of the jet pump, and a MP liquid return valve for controlling the flow of MP liquid * ,* through the liquid return line, wherein the MP liquid return valve is constructed and arranged to be controlled according to the sensed pressure of the HP liquid at the S..

HP inlet of the jet pump. S. ** * I *

* ,

11. An apparatus according to any preceding claim, including a cooler device for S.....

* cooling MP liquid flowing through the liquid return line.

12. An apparatus according to any preceding claim, including a gas outlet line for separated MP gas and a liquid outlet line for separated MP liquid.

13. An apparatus according to any one of claims I to 11, including a co-mingling device having a gas inlet connected to receive separated MP gas, a liquid inlet connected to receive separated MP liquid, and a multiphase outlet line for the combined MP fluid.

14. A method of boosting the pressure of flowing fluids, the method including delivering LP fluid to a LP inlet ofajet pump, delivering HP liquid to a HP inlet of the jet pump, combining the LP fluid with the HP liquid in the jet pump to form MP fluid, delivering the MP fluid from a MP outlet of the jet pump to a MP separator device, drawing separated MP gas from a MP gas outlet of the MP separator, drawing separated MP liquid from a MP liquid outlet of the MP separator, boosting the pressure of at least some of the separated MP liquid with a mechanical pump, and returning the pressure boosted liquid to the HP inlet of the jet pump.

15. A method according to claim 14, including receiving LP multiphase fluid, delivering the LP multiphase fluid to a LP separator, separating the LP multiphase fluid to form LP gas and LP liquid, delivering the separated LP gas to the LP inlet of the jet pump, combining the separated LP liquid with at least some of the separated MP liquid, boosting the pressure of the combined liquid with a mechanical pump, and returning the pressure boosted liquid to the HP inlet of the *1**** Jetpump.

16. A method according to claim 15, including sensing the level of LP liquid in the LP separator, and controlling the flow of LP liquid through the LP liquid outlet of the LP separator according to the sensed level.

* .

17. A method according to claim 15 or claim 16, including sensing the pressure of the LP gas at an LP gas outlet of the LP separator, and controlling the flow of LP gas through the LP gas outlet according to the sensed pressure.

18. A method according to claim 14, including receiving LP multiphase fluid and delivering the LP multiphase fluid to the LP inlet of the jet pump.

19. A method according to any one of claims 14 to 18, including sensing the level of MP liquid in the MP separator, and controlling the flow of MP liquid through a MP liquid outlet line according to the sensed MP liquid level.

20. A method according to any one of claims 14 to 19, including sensing the pressure of the MP gas at the MP gas outlet of the MP separator, and controlling the flow of MP gas through the MP gas outlet according to the sensed MP gas pressure.

21. A method according to any one of claims 14 to 20, including sensing the pressure of the HP liquid at the HP inlet of the jet pump, and controlling the flow of MP liquid returned to the HP inlet of the jet pump according to the sensed HP liquid pressure.

22. A method according to any one of claims 14 to 21, including cooling the MP liquid returned to the HP inlet of the jet pump.

23. A method according to any one of claims 14 to 22, including co-mingling the separated MP gas with at least at least some of the separated MP liquid, and delivering the combined MP multiphase fluid through an outlet. S. *. * *.* S... * S S... * .* * . . * *5 S.. S. *I * S * * S

S

S..... S *