Patent Application
20110042093
The present invention is related to subsea equipment and pumping systems, more particularly subsea modules located on the sea bed, preferably away from the production well and designed to pump to the surface hydrocarbons with a high associated gas fraction that is produced by one or more subsea production wells.
Prospecting and production from wells in fields producing hydrocarbons located in increasingly deep water is accompanied by technical difficulties and an increase in the complexity of the operations which have to be performed.
Production of hydrocarbons in the high seas requires that production and injection wells be drilled beneath the sea and that subsea equipment must also be installed. Many of these wells produce hydrocarbons in the form of liquid and gas. The higher the gas fraction, the greater the difficulty encountered in pumping operations, as the presence of gas is prejudicial to pump performance, and sometimes rules out the use of this method of lifting.
A list of possible items of equipment which might be installed in association with subsea production and injection wells and other equipment used, with their acronyms widely known to specialists, is provided immediately below, and these will be used to identify the corresponding equipment mentioned in this document below:
Other items of equipment which are found alongside those mentioned above which also have to be installed beneath the sea are: subsea separating units (water/oil or gas/liquid), subsea heaters, electrical transformers, and pig launching systems.
An SPU may be built and located on a vessel, a fixed platform or even onshore. When these SPUs are built on vessels' hulls and provide capacity for the processing, storage and discharging of oil they are known as FPSOs.
Normally, production wells are at a distance of some kilometres from the SPU.
In order for the fluids produced from a well to be able to flow towards an SPU at the high flows required to maintain the economic attractiveness of a project, energy, generally in the form of pressure, must be provided to the fluid.
A variety of artificial lifting methods have been used to increase the flows of production fluid. One of these methods uses pumps such as ESPs installed at the bottom of oil-production wells which are generally driven by electric motors.
Under particular conditions the abovementioned pumps may be mounted within modules installed on the sea bed. Known as pumping modules, they may also use other types of pumps, which are not ESPs, such as for example multiphase pumps. The difference lies in the geometry of these two types of pump. Whereas ESPs are designed to be installed within production wells and therefore have to have a long slender geometry, multiphase pumps have a compact geometry because their design envisages that they will be operated and installed on the sea bed away from the production well.
U.S. Pat. No. 4,900,433 by the British Petroleum Company p.l.c. shows an arrangement in which a pump similar to an ESP is installed within a false well, known by specialists as a dummy well, which is created with the aim of accommodating a (liquid/gas) separation and pumping system. The flow of gas-free hydrocarbons is pumped by an ESP as long as the gas flow flows naturally because the back pressure in the gas riser is low.
In this system it is essential that a level control system of a sophisticated type be used, together with control of liquid/gas separation, which in the case in point is carried out by means of a complex system. In addition to this there must be at least two production lines, one for the liquid phase and the other for the gas phase.
In addition to increasing costs, this proposal does not appear to be very efficient, given that as the gas is separated off and removed lifting energy associated with that gas is also removed, and this directly implies the use of high-powered pumps and a very great increase in pressure, especially in the case of deep water.
Brazilian patent application PI 0301255-7 by the present Applicant, and wholly incorporated here by reference, teaches that it is possible to use a pumping module directly connected to subsea equipment, such as for example a wellhead/subsea christmas tree assembly comprising a closed tubular body and a hydraulic connector, in which the connector is connected to an existing terminal in the subsea equipment.
It is also known from U.S. Pat. No. 6,419,458 and U.S. Pat. No. 6,688,392 that it is possible to install a motorised pump unit, similar to an ESP, hydraulically linked to a dummy well, both to produce oil and to inject water or other fluids into the oil reservoir.
From U.S. Pat. No. 6,497,287 and U.S. Pat. No. 6,705,403 it is known that it is possible to install a submersible pump in combination with a pump of the jet type and a gas separator in production wells, making it possible to produce oil with high gas fractions. The disadvantage of this method, mainly in the case of subsea completion (subsea wells), is the great concentration of equipment within the production well, which if a fault should occur requires long-term action on the well (tens of days) in order to make a repair, and this involves removal the column, which requires a very expensive rig.
On the other hand, in U.S. Pat. No. 5,562,161, it is stated that it is possible to install and recover a jet pump driven by injected gas lift within the annulus of the well through an operation involving wire or flexible piping.
On the basis of Brazilian patent applications PI 0400926-6, PI 0404603-0 and PI 0500996-0, all by the Applicant, and incorporated in full herein by reference, it is taught that it is possible to install a PUMO within a lined hole (or a driven hollow pile) in the sea bed.
Nevertheless, because of the substantially vertical geometry of the module, which is tens of metres in length, there is also a greater possibility that a retention space will form and block gas at its top, adversely affecting pump suction.
In Brazilian patent application PI 0403295-0, also by the Applicant, there is a description of an installation comprising at least two or more pumping units on independent modules mounted on structures also known as skids which are supported directly on the sea bed.
There are in the art compact pump models which can be installed on the sea bed, which are alternatives to mounting on skids or incorporation into wellheads.
There are advantages associated with the use of pumps of the ESP type, given that these items of equipment are manufactured on a large scale and are of low cost. Conversely, the slender geometry of this type of pump gives rise to parallel development of solutions for their accommodation, as already mentioned above, and the main restriction on the installation of these pumps outside a production well is their low tolerance to flows of fluid with high fractions in terms of gas.
There is in the present art no system which is equipped with ESPs with a greater tolerance to gas, having a geometry and associated devices which facilitate the work of installation and removal and which can be integrated with other subsea systems.
This invention relates to a pumping module and subsea pumping system using such a module for the production of hydrocarbons with a high gas fraction, designed to pump hydrocarbons with a high associated gas fraction produced by a subsea production well to the surface.
One aspect of this invention involves a subsea pumping module equipped with conventional pumps for the pumping of substantially liquid phases, of for example the ESP type, in combination with another type of pump which has characteristics having a greater tolerance to gas, such as for example a jet pump or a flow pump.
For this purpose the multiphase flow is divided into two streams: one which is gas-poor and another which is gas-rich. Each of these streams is separately pumped by different equipment, which opens up new possibilities for the application of this equipment and at the same time improves tolerance to gas fractions.
The pumping system according to this invention has a configuration which is interlinked with the pumping module and preferably housed in a lined hole in the sea bed. A gas-liquid separator in the pumping module preferably separates the hydrocarbon production flow into a first flow which is substantially rich in liquid phase and a second flow which is substantially rich in gas phase.
The first flow is delivered to a first pump which is more suitable for the pumping of liquids. The second flow is delivered to a second pump which is more suitable for the pumping of fluids which are rich in the gas phase.
The drive fluid for the second pump can be selected from the flow of fluid originating from the first pump outlet in the pumping module and a fluid compatible with the process and offshore oil production, for example originating from the SPU, and which may be: gas lift, dead oil or water.
The module may be housed within a lined hole or hollow pile, or housed on a skid base supported on the sea bed.
In a first aspect, the invention comprises a subsea module for installation on the sea bed, the subsea module being for pumping to the surface hydrocarbons that have a high associated gas fraction that have been produced by a separate subsea production well, said subsea module comprising:
The first pump (4) is preferably a pump of the ESP type.
The second pump (8) is preferably a jet pump.
The second pump (8) is usefully located and constructed so that the outlet flow of the liquid phase stream pumped by the first pump (4) sucks in the gas phase stream.
In another embodiment, the module further comprises:
The separator equipment (3) may be of the cyclone type.
The module is preferably located at a place on the sea bed which may be selected from a lined hole (F) and a hollow pile (E).
The module may have at its top an extension in the form of a gas chamber (11) within which the second pump (8) may be installed.
The module may comprise a check valve to prevent a backflow of gas from the second pump. Any such check valve may be at the top of the module. Aany such check valve may be located at the connection between said gas chamber (11) and the top of the module housing;
The separator equipment (3) is preferably located internally at the top of the module.
The module may comprise a suction pipe (6) for transporting the gas phase separated by the separator equipment (3) located at the top of the module (1) where the gas phase accumulates.
The second pump (8) is preferably located internally at a point along the length of the outlet pipe (9).
The first pump is usually poorly tolerant for pumping a gas phase.
The second pump is usually poorly tolerant for pumping a liquid phase.
The components of the module are preferably housed in a capsule (1), which can have externally at its top an interface (I) for the attachment of an installation and removal tool.
The module may comprise a hydraulic connector (10) connected to the outlet pipe (9). This facilitates connection to the stationary production unit and/or the production well.
The first pump (4) is preferably located below the separator equipment (3).
The first pump is preferably driven by an electric motor (M) powered by an electrical cable (F).
The module may comprise a fluid directing pipe (5), known to specialists by the term “shroud”, that encloses the first pump (4) forming a capture region which directs the liquid phase to the inlet (41) of the first pump (4).
Any drive fluid pipe (12) may be connected to the hydraulic connector (10).
The inlet pipe (2) is preferably connected to the hydraulic connector (10).
The invention also provides in another aspect a subsea pumping system for the production of hydrocarbons with a high gas fraction, said system comprising a stationary production unit and a pumping module installed on the sea bed alongside an oil production well (P), comprising:
In a yet further aspect, the invention provides a subsea pumping system for the production of hydrocarbons with a high gas fraction, said system comprising a stationary production unit and a pumping module installed on the sea bed alongside an oil production well (P), comprising:
The pumping module of any one of the embodiments can be mounted on a base (S) supported on the sea bed.
Preferably, when oil is pumped in from the production well (P), the well pump (13) increases the energy of the fluid in the form of pressure and transmits this increase in energy in the form of an increase in suction pressure to the second pump (8) of the subsea module (PM) which as a consequence reduces the fraction of free gas, increasing the flow produced.
In a yet further aspect, the invention provides a method for pumping hydrocarbons to the surface, said method comoprising:
mixing the gas and liquid phases and transporting the mixture to the surface.
In this method, the second pump is preferably a jet pump and the step of using the second pump preferably comprises sucking the gas phase into the liquid phase using the flow of the liquid phase provided by the first pump.
The method is preferably carried out in a dummy well alongside the production well, with the oil being provided to the top of the dummy well such that the gas and liquid phases separate as the oil flows downwardly.
In another embodiment, the invention comprises a subsea module installed on the sea bed, preferably away from a production well and intended to pump hydrocarbons having a high associated gas fraction produced by a subsea production well to the surface, characterised in that it comprises:
Preferably, in this module the first pump (4) is a pump of the ESP type and the second pump (8) is a jet pump.
Preferably, in this module the separator equipment (3) is of the cyclone type.
Preferably, in this module the second pump (8) is located within the outlet pipe (9) so that the outlet flow of liquid phase pumped by the first pump (4) sucks in the gas phase captured by the suction pipe (6) of this second pump (8).
In another embodiment, a module is provided that comprises all the elements in the preceding embodiment, except:
Preferably, the module is located at a place on the sea bed which may be selected from a lined hole (F) and a hollow pile (E).
Another embodiment of the invention provides a subsea pumping system for the production of hydrocarbons with a high gas fraction comprising a pumping module (PM) installed on the sea bed alongside an oil production well, characterised in that it comprises:
Another embodiment of the invention provides a subsea pumping system for the production of hydrocarbons with a high gas fraction which comprises a pumping module (PM) installed on the sea bed alongside an oil production well, characterised in that it comprises:
The subsea pumping system may comprise one of the embodiments already described for the pumping module (PM) mounted on a base (S) supported on the sea bed.
Preferably, in these embodiments, when oil is pumped in from the production well (P) the well pump (13) increases the energy of the fluid in the form of pressure and transmits this increase in energy in the form of an increase in suction pressure to the second pump (8) of the subsea module (PM) which as a consequence reduces the fraction of free gas, increasing the flow produced.
The characteristics of the pumping module and system for the subsea pumping of hydrocarbon production with a high associated gas fraction will be better understood from the following detailed description, purely by way of example, associated with the drawings mentioned below, which form an integral part of this description and in which:
A detailed description of the pumping module, system for the subsea pumping of hydrocarbon production with a high associated gas fraction and corresponding methods will be provided on the basis of the identifications of the components based on the figures described above.
This invention relates in one aspect to a module and subsea pumping system for the production of hydrocarbons with a high gas fraction which is designed to pump hydrocarbons with a high associated gas fraction produced by a subsea production well to the surface.
One aim of this invention is achieved through the design of a pumping module (PM) which is interlinked with pumping equipment already present in the production well.
The first pump (4) is preferably a pump of the ESP type. The second pump (8) may be any one useful for pumping a gas phase and is preferably selected from a jet pump and a flow pump.
In this embodiment the second pump (8) is a jet pump.
The separator equipment (3) is preferably of the cyclone type. This tuype of separatot cauises the fluid to undergo cicular motion, which helps to release the gas from the liquid. Upon separation, the gas usually moves upwards and the liquid usually flows downwards.
The second pump (8) is in this embodiment located within an outlet pipe (9) so that the outlet flow of the liquid phase pumped by first pump (4) sucks in the gas phase captured by the suction pipe (6) of this second pump (8).
In this embodiment, the capsule (1) preferably has at its top an extension in the form of a gas chamber (11) within which the second pump (8) can be installed. Preferably, at the connection between gas chamber (11) and the top of the housing, there is a check valve (7) which is used to prevent the backflow of gas.
The flow of drive fluid originating from the SPU to drive the second pump (8) can be selected from gas lift, dead oil, less viscous oil, water or another fluid compatible with the production process.
The pumping module (PM) is preferably housed at a locality on the sea bed which may be selected from a lined hole (F) and a hollow pile (E). Alternatively, the module may be mounted on a skid.
A subsea pumping system for the production of hydrocarbons with a high gas fraction, another aspect of this invention, can be seen in the first embodiment in
It will be noted that the illustrated system comprises:
The subsea pumping system for the production of hydrocarbons having a high gas fraction according to this invention can be seen in a second embodiment in
It will be noted that this system comprises:
The pumping system according to this invention may be embodied in a third way which may comprise any of the embodiments already mentioned for the pumping module (PM) fixed on a base (S) known to specialists by the term skid supported on the sea bed, which is not shown in any Figure in this description.
When oil is pumped in from the production well (P), the well pump (13) increases the energy of the fluid in the form of pressure and transmits this increase in energy in the form of an increase in suction pressure to the second pump (8) of the subsea module (PM) which as a consequence reduces the fraction of free gas, increasing the flow produced.
The description of the pumping module and system for the subsea pumping of hydrocarbons to which this invention relates provided hitherto must be regarded only as possible embodiments and means, and any particular features included in them should be understood as only things which have been described in order to aid understanding. This being the case, they cannot in any way be regarded as restricting the invention, which is only restricted by the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| PI0703726-0 | Oct 2007 | BR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2008/003438 | 10/10/2008 | WO | 00 | 9/16/2010 |
