The present invention relates to a pump assembly and in particular, but not exclusively, to a pump assembly using jet pumps for use in the oil and gas industries.
Jet pumps or eductors are passive devices that use energy from a high pressure (HP) fluid source to boost the pressure of a low pressure (LP) fluid. The terms jet pump, eductor, ejector and gas jet compressor are used in various industries and refer to the same general type of device.
Jet pumps have been used successfully in a variety of applications onshore or near the bottom of oil or gas wells. The HP flow is gas or a high pressure liquid such as oil or water. The LP flow could be gas, or liquid (oil and water), or a mixture of the two.
In applications such as those for the oil and gas industry, the operating conditions often change with time. These changes may demand changes to the jet pump design or the internal dimensions of the jet pump in order to optimise the design and get the best performance under the new conditions. These changes demand using a new jet pump with new dimensions for its internal key components such as the nozzle and the mixing tube. Supplying and installing the new jet pump is costly and may require that production is interrupted for a substantial period.
Jet pumps with interchangeable internals (the nozzle assembly, and the mixing tube/diffuser assembly) have been designed and supplied. An example is shown in
In some applications, only a change in the nozzle of the jet pump may be necessary. For such applications a multi-nozzle pump assembly has been proposed, as shown in
With increases in the applications of jet pumps and the development of new subsea production systems there is a need for a jet pump assembly suitable for subsea applications. Subsea production systems may consist of a variety of components such as manifolds, valves and in some cases booster pumps and separators, all of which are located on the sea bed to avoid the need for costly offshore platforms. All equipment that is installed subsea for any function needs to be highly reliable, with little to no maintenance requirement or changes to design requiring retrieval of the unit to surface, as the cost of retrieving such units for maintenance, repair, or modification is very high, especially in deep water applications.
It is also desirable in many offshore platforms to minimise maintenance work, and to minimise the need to isolate and de-pressurise the jet pump and replace its internal components.
It is an object of the present invention to provide a pump apparatus that mitigates one or more of the aforesaid disadvantages.
According to one aspect of the present invention there is provided a pump assembly comprising a housing and a plurality of jet pumps arranged within the housing, wherein the housing includes a HP inlet, a LP inlet and an outlet and is divided internally by partitions into a HP zone, a LP zone and an outlet zone, said partitions comprising a first partition between the HP zone and the LP zone, and a second partition between the LP zone and the outlet zone, said LP zone being located longitudinally between the HP zone and the outlet zone, and each jet pump includes a nozzle assembly, a mixing tube and a diffuser and comprises an elongate tubular body having an HP inlet at a first end of the body, an outlet at a second end of the tubular body and a LP inlet between the first and second ends, wherein each jet pump is mounted within the housing with the HP inlet located in the HP zone, the LP inlet located in the LP zone, and the outlet located in the outlet zone, and each jet pump extends through and is sealed to the first and second partitions.
By providing a plurality of jet pumps within a single housing, it is possible to adapt the pump apparatus to different flow rates and different flow regimes (for example, different proportions of gas and liquid). This ensures high efficiency over a wide range of flow regimes and capacities. Further, because each jet pump includes a nozzle assembly, a mixing tube and a diffuser, it is capable of efficient operation, as the nozzle assembly may be matched specifically to the mixing tube and the diffuser design.
The pump assembly can also be modularised, consisting of a number of standard, off-the-shelf, components that can be selected according to specific production conditions including, for example, the flow rate, pressure and flow regime of the produced fluids. These components can then be assembled relatively quickly and easily, allowing a custom-designed pump assembly to be supplied quickly and at relatively low cost.
Preferably, each jet pump is sealed to the partitions, for example by means of O-ring seals or by welding.
Preferably, the housing is T-shaped, having a longitudinal axis and a transverse axis, the HP inlet being located at one end of the longitudinal axis, the outlet being located at the opposite end of the longitudinal axis and the LP inlet being located on the transverse axis. Advantageously, the housing comprises a T-section pipe.
Preferably, at least some of the jet pumps have common external dimensions. More preferably, all the jet pumps have common external dimensions, or they all have “standard” external dimensions, selected for example from two or more alternative sets of dimensions.
Preferably, at least one of the jet pumps is substantially cylindrical having a HP inlet at one end, an outlet at an opposite end and a LP inlet in a side thereof.
Advantageously, the pump assembly includes isolation means for isolating at least one of the jet pumps. This allows individual jet pumps to be turned on or off, thereby adapting the system to changes in operating conditions.
The isolation means preferably comprises means for stopping the HP inlet, the LP inlet and/or the outlet of at least one of the jet pumps. Preferably, the isolation means comprises means for stopping two of the three inlet and outlet vents.
The pump assembly preferably includes an actuator for actuating the isolation means to isolate individual jet pumps, allowing the system to be adapted to changes in operating conditions from a remote location. This is particularly helpful in apparatus intend for use in subsea operations. Preferably, the actuator comprises a hydraulically-driven valve.
In a preferred embodiment, the invention provides a modularised, multi jet pump unit, which allows the operator to use any number of standard jet pump units as needed, depending on the field conditions, without having to isolate the system, remove the old internals and introduce new sets of internals. Each jet pump unit consists of the same key components of a nozzle, a mixing tube and a diffuser. The multiple jet pump units are housed in a containment pressure vessel or pipe section for ease of handling and for isolating the system against exposure to subsea environment, or in the case of offshore platforms achieve the full pressure rating of the total jet pump system. The key features of the new system are described below.
Certain embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:
The pump assembly shown in
In this example, the housing 50 comprises a T-section pipe is T-shaped having a longitudinal axis and a transverse axis. An HP inlet 54 is located at one end of the longitudinal axis, an outlet 56 is located at the opposite end of the longitudinal axis and a LP inlet 58 is located on the transverse axis. The HP and LP inlets 54, 58 and the outlet 56 are each provided with flanges 60 for connection to external pipelines (not shown).
The housing 50 is divided internally into a HP zone 62, a LP zone 64 and an outlet zone 66 by two partition walls 68, 70 the LP zone being located longitudinally between the HP zone and the outlet zone. The first partition wall 68 is located between the HP zone 62 and the LP zone 64, and the second partition wall 70 is located between the LP zone and the outlet zone. Each of these partition walls 68, 70 includes a plurality of apertures 72 for receiving the individual jet pumps 52. In the embodiment shown in
Each jet pump 52 is substantially cylindrical comprising an elongate tubular body 73 having a HP inlet 74 at a first end of the body, an outlet 76 at a second end of the body and a LP inlet vent 78 in a side of the body between the first and second ends thereof. It is supported by the partition walls 68, 70 so that the HP inlet 74 is located in the HP zone 62, the LP inlet 78 is located in the LP zone 64 and the outlet 76 is located in the outlet zone 66. Internally, each jet pump 52 includes a nozzle assembly 80, a mixing tube 82 and a diffuser 84.
O-ring seals 86 are provided on the external cylindrical surface of the jet pump 52 to form a hermetic seal with the two partition walls 68, 70. Alternatively, the jet pumps 52 may be welded permanently to the partition walls 68, 70.
As shown in
If the jet pumps 52 are identical, the capacity of the pump apparatus can be adjusted by increasing or decreasing the number of isolated jet pumps. Alternatively, jet pumps 52 with different flow capacities can be fitted to provide a wider range of flow capacity, or different types of jet pump can be used so that the pump apparatus can be adapted to different flow regimes (for example, different amounts of gas and liquid).
Preferably, the jet pumps 52 all have identical external dimensions (even if they have different flow capacities or are of different types), so that they can be supplied as standard “off the shelf” products, which can then be selected and fitted into a standard housing, according to the requirements of the application for which they are intended, including for example the flow rate, pressure and flow regime of the produced fluids.
If the plugs 88 are fitted manually, for example by screwing them into the ends of the jet pump 52, it will be necessary first to depressurise and isolate the pump apparatus, so as to provide access to the jet pumps. Although this is a somewhat time-consuming process, it is nevertheless considerably quicker and less expensive than adapting or removing and replacing a conventional jet pump.
For subsea installations, it may be impractical to change the configuration of the pump apparatus manually. A pump apparatus intended for use in this situation may therefore be provided with actuator-operated plugs for isolating individual jet pumps. These plugs may for example be hydraulically actuated.
In this example a piston 95 is provided at the HP inlet end of the jet pump unit 52. The regions of the jet pump body on either side of the piston 95 are isolated by ring seals 98. These seals 98 isolate fully the small gap between the outer surface of the piston 95 and the inner surface of the jet pump 52. The piston 95 can slide along the inner body of the jet pump to expose or to isolate a port 96, which comprises the HP inlet through which HP fluid enters the jet pump. There is a seal ring 97 around the port 96, which acts with the piston 95 to seal the HP inlet and prevent the passage of fluids beyond the port 96.
Under operating mode a spring 94 pushes the piston 95 to a position which exposes the port 96 and opens the flow passage into the jet pump. When the piston 95 is to be moved to cover and seal the port 96, hydraulic fluid is injected via a line 92 into a pressure chamber 93 between the piston 95 and a removable screwed end cap 91. This pressure pushes the piston 95 against the spring 94 and closes the port 96.
Such a piston assembly or similar can be applied to both the discharge end and the HP inlet end of the jet pump.
In summary, according to an embodiment of the invention, the multi jet pump assembly consists of several small standardised jet pumps assembled to operate in parallel. The number can be any, varying from two to several, depending on the application. The system is designed so that at any time any number of jet pump units can be operational to match the operating conditions of that time. All units can be of identical external design to minimise cost, or if needed they can consist of two or more groups of similar size. In this case each jet pump is always of optimum design as it always handles the flow for which it was designed, even if the total HP or LP flow changes significantly.
This feature has a number of benefits which justify its use for subsea or offshore applications:
The system therefore consists in a preferred embodiment of the following key features as shown in
Number | Date | Country | Kind |
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1110692.9 | Jun 2011 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB2012/000533 | 6/19/2012 | WO | 00 | 3/21/2014 |