Patent Application
20100025043
The present patent application relates to a system for operation and service of hydrocarbon-producing wells, a vessel for use in operation and maintenance of hydrocarbon-producing wells and a method for intervention on subsea equipment which is in use in connection with production and further transport of a well stream.
The principle is known of producing oil and gas from a ship lying anchored/DP-positioned over a subsea field of hydrocarbons. Until now the main task of this ship has been to receive, process and store the well stream. The unprocessed well stream is processed and electric power and other energy required for running the process is generated on board the ship. In recent years systems have been developed where parts of the processing equipment are located on the seabed, for example multiphase pumps and water injection pumps. In this case, electric power is passed in a riser/umbilical system from the ship down to the bottom-mounted equipment. Where environmentally vulnerable areas are involved, it is desirable to reduce the environmental exposure to a minimum during the production of oil and gas. Concepts are therefore being considered which are based on transportation of unprocessed well stream in pipelines from the field to a land-based plant or processing plant on other adjacent platforms or floating platforms for further processing. The principal challenge with concepts of this type appears to be the actual pipe transport (flow assurance problems) and operation of pressure booster equipment such as multiphase pumps and wet gas compressors with associated electric power system. When the field and the land-based plant are at a great distance apart, offshore power generation seems to be the most attractive solution.
From the prior art, in U.S. Pat. No. 6,2363,971 B1 a system is disclosed for subsea production of hydrocarbons where an intermediate platform is arranged between the seabed and the water surface and a floating platform on the surface. The well stream is taken up to the intermediate platform on which are mounted various pieces of equipment including pumping equipment and equipment for measuring volume flow. Gas from the produced well stream can be separated and taken up to the floating platform where it is used for production of electrical energy, while a riser connected to the intermediate platform transports the rest of the well stream to a processing destination near the hydrocarbon field.
In GB 2 292 760 A a production vessel is disclosed, the aft end of which is provided with a device for receiving a buoy, and round which the vessel can pivot, the vessel being anchored to the bottom. The risers transporting the well stream are connected to the buoy. At the other end of the vessel a rig is provided for use in maintenance of the production well.
U.S. Pat. No. 6,364,021 B1 discloses a system comprising a riser from the wellhead to a floating buoy on the ocean surface. The system further comprises a vessel which can go alongside the buoy and conduct predetermined maintenance operations.
The proposed system seeks to provide an integrated system for production of hydrocarbons from subsea wells which will have a number of advantages when compared with the prior art.
Since the hydrocarbons will not be processed on the vessel, the normal processing equipment will be superfluous, and this results in a number of advantages. Since the vessel will not be provided with processing equipment, the usual “rules and regulations” applying to production vessels are avoided, thereby making the vessel cheaper to build. When the vessel has no processing equipment on board, space is also made available for storing, for example, equipment for use in intervention on subsea equipment, spare parts, pigs and equipment for launching pigs, chemicals for injecting into the well stream, fuel for energy production, etc. The fact that the well stream is not taken up to the vessel for processing also reduces the environmental risk associated with production, an aspect of offshore production of hydrocarbons which will become increasingly important in the future. Another advantage of the system is the possibility it offers of simultaneous intervention and production, which may be important for maintaining flow and temperature in the transport pipe.
An object of the invention, therefore, is to provide a system for offshore production of hydrocarbons where the risk of accidents resulting in environmental damage is reduced.
Another object of the invention is to provide a system which permits the combination of power generation and intervention on subsea installations.
A further object of the present invention is to provide a system for offshore production of hydrocarbons with improved assurance of uninterrupted production of hydrocarbons, and particularly assurance that the transport system for the hydrocarbons is in continuous operation.
It is also an object of the invention to provide a system which results in simplified operation and maintenance of subsea equipment, such as well, wellhead, pressure booster equipment and other equipment disposed below the surface of the water.
This is achieved by means of a system according to claim 1, a vessel according to claim 16 and a method according to claim 22. Further preferred embodiments of the invention are indicated in the dependent claims.
A system is provided for operation and service of at least one hydrocarbon-producing well, and of equipment for further transport of the well stream and any equipment required for treatment of the well stream. The equipment and the at least one well are disposed below a water surface, preferably on a seabed or an ocean floor. The system further comprises at least one pipeline for transport of the well stream to the desired destination, and at least one pressure booster unit for driving the well stream through the at least one pipeline, a vessel for operation and service of the at least one well and the equipment disposed below the water surface, where the vessel comprises means for controlling operating and service functions, together with means for conducting an intervention on equipment disposed below the water surface. The system further comprises means for production of energy for operation of the equipment disposed below the water surface, as well as means for transferring energy from the means for production of energy to at least the at least one pressure booster unit which drives the well stream of hydrocarbons through the at least one pipeline and means for communication with and control of the at least one well and the equipment disposed below the water surface.
The system may also comprise two or more hydrocarbon-producing wells. In this case a pressure booster unit may be mounted at each well or the system may be provided with a pressure booster station where the well streams from the hydrocarbon-producing wells are gathered and pressurised. From the pressure booster station at least one pipeline is provided for further transport of the well streams to the desired destination.
In a preferred embodiment the vessel is provided with an anchoring system comprising a mooring system, a dynamic positioning system or a combination of the two.
The anchoring system will advantageously be arranged in such a manner that the vessel can rotate about the anchor point on the vessel or swivel around the anchoring system when the vessel is anchored via one or more mooring lines to an anchored buoy. The buoy may be arranged in such a manner that it is lying on the surface of the water or it may be arranged so that it is located between the surface and the bottom. The vessel will then be able to pivot round the buoy. It will also be possible to fasten the vessel directly to an anchor on the seabed or ocean floor, in which case the vessel will be able to pivot round this point. When the vessel is anchored to a buoy, risers or umbilicals may be arranged in such a manner that they either extend from the vessel to the buoy and from there on to a swivel device at the anchor on the bottom, or they may extend directly from the vessel down to the swivel device at the anchor on the bottom.
When one or more adjacent wells are developed, it will be advantageous to place essential equipment, which has to be disposed below the water surface, under or within the curve described by the vessel's outer point as the vessel rotates about or swivels around the anchoring system, i.e. the vessel rotates about an anchor point in the vessel or pivots around a buoy to which the vessel is anchored. This will make it easy to position the vessel when maintenance or repairs have to be carried out on equipment located below the surface of the water, and preferably on the seabed or ocean floor.
The vessel is advantageously arranged so that it can be disconnected from its anchoring system and riser and umbilical system for positioning over the intervention object on the seabed or ocean floor if this object is not located within the above-mentioned curve. This will also be advantageous in bad weather when it may be necessary to perform a rapid disconnection of the anchoring system and riser and umbilical system.
The means for production of energy for operation of equipment disposed below the water surface may either be mounted in its entirety on the vessel or in its entirety below the water surface. Parts of the means for energy production may possibly be mounted on the vessel, while the rest of the means are mounted below the water surface.
In order to provide energy, the system may be provided with means below the surface of the water, preferably on the seabed or ocean floor in connection with the well or the at least one pipeline, in order to remove a part of the gas in the well stream together with means for transporting the gas up to the vessel. The transport of gas up to the platform may be carried out by means of a separate pipeline or through an umbilical, which is also used for other purposes in connection with the operation of the well.
One of the advantages of not taking the well stream of hydrocarbons up to the vessel for processing is that the vessel is not encumbered with all the processing equipment with which the production vessels are normally equipped today. This absence of processing equipment for processing the well stream makes a great deal of space available on the vessel. The vessel is therefore provided with storage capacity for necessary contributory factors in connection with operation and maintenance of the system, such as chemicals for injecting into the well stream, pigs and equipment for launching and receiving pigs, spare parts and equipment for use in intervention on equipment below the water surface and possibly fuel required for energy production.
In order to ensure that the stream of hydrocarbons in the at least one pipeline does not come to a stop, the system may be provided with means for transferring chemicals from the vessel to the at least one pipeline. These are chemicals which are injected in order to prevent the formation of wax and hydrate in the pipes and they can be transferred from the vessel by means of a separate pipeline or through an umbilical which is also used for other purposes in connection with the operation of the well or wells. The system is also provided with necessary equipment such as valves for injecting the chemicals into the well stream in the pipeline.
The system will also advantageously comprise means for launching and receiving pigs in the at least one pipeline and means for transferring pigs down from the vessel to the at least one pipeline or from the at least one pipeline to the vessel. These may be pigs for scraping and cleaning the at least one pipeline in order to avoid shutdown or they may be intelligent pigs that are passed through the at least one pipeline for inspection of the pipeline's integrity.
The system may also advantageously comprise heating means for heating the at least one pipeline as an additional preventive measure against stoppage of the production of hydrocarbons, as well as means for transferring energy from the vessel required for the heating means provided in connection with the at least one pipeline. The energy transferred from the vessel to the at least one pipeline will preferably be electrical energy, and the means for transferring the energy from the vessel to the at least one pipeline will therefore be an electric cable. This may be a separate cable or it may form a part of an umbilical. These heating means for the at least one pipeline may extend over a shorter or longer distance along the pipeline which transports the hydrocarbons to the desired destination where processing will take place. The heating means may also be arranged along the entire length of the pipeline.
In addition to the equipment already mentioned above, the system may also include additional equipment for treatment of the well stream, disposed below the surface of the water, and particularly on the seabed or ocean floor. This may include equipment for mixing, desanding and water separation.
Furthermore, it will be necessary to monitor the production of hydrocarbons and the rest of the system. The system will therefore advantageously include means for communicating production and control data from the at least one well and other equipment, which is disposed below the water surface, to the vessel. Similarly, the system will advantageously include means for transferring control signals from the vessel to the at least one well and other equipment disposed below the surface of the water. Such signals will normally be transmitted through an umbilical containing both electric cables for electrical signals and pipes for hydraulic or pneumatic signals.
A vessel is also provided for use in connection with operation and maintenance of a system for production of a well stream containing hydrocarbons from at least one well, where the at least one well and the equipment are disposed below a water surface, particularly on a seabed or an ocean floor. The vessel is provided with a system for anchoring, e.g. a mooring system, a dynamic positioning system or a combination of the two.
Furthermore, the vessel may advantageously comprise means for production of energy for operation of equipment disposed below the water surface, and also possibly for heating at least one pipeline disposed below the water surface.
Moreover, the vessel may advantageously comprise means for transferring chemicals to at least one pipeline disposed below the water surface. The chemicals are added to the well stream in order to prevent hydrate formation and they can be transferred from the vessel to the at least one pipeline through a separate pipeline or through an umbilical which can also be used for other purposes in connection with the production of the hydrocarbons.
Moreover, the vessel may advantageously comprise storage space for storing the chemicals which are to be injected into the pipeline as explained above.
Furthermore, the vessel may advantageously comprise means for carrying out an intervention on equipment disposed below the water surface. These means include tool systems which can be lowered through an opening in the vessel or from a lifting arrangement which is normally located at the after end of the vessel. The anchor point and location of the equipment for lowering and raising the tool systems will normally be located in different parts of the vessel so that the vessel covers a greater area when it rotates or pivots round the anchor. The tool system used in a given situation will be dependent on what kind of equipment is to be worked on and which operations have to be performed on the equipment.
Furthermore, the vessel may advantageously comprise storage space for storing tool systems and equipment used during intervention on equipment below the water surface and spare parts for said equipment below the water surface. In particular this will be parts for equipment which is critical for the production of hydrocarbons and for ensuring that the well stream can flow uninterruptedly through the at least one pipeline.
Furthermore, the vessel may advantageously comprise means for transferring pigs to a pipeline disposed below the water surface. A pig is transferred from the vessel to a subsea receiving station either in a tool which is lowered and connected to the at least one pipeline or in a flexible transfer riser which may be secured to the at least one pipeline's pig launching system which can be hoisted up to the vessel as required. The pig is installed in a controlled environment on the vessel and passed through the flexible riser in a controlled manner down to the pig receiving system. It is expedient to pass both sophisticated instrument pigs through the pipe in order to monitor the pipe's integrity and simpler scraper pigs to remove wax, sand, water, etc. that have been deposited in the pipe.
Furthermore, the vessel may advantageously comprise storage space for storing pigs and equipment for transferring pigs to the pipeline.
The anchoring system may be arranged in such a manner that the vessel rotates about an anchor body on the vessel. Anchor lines extend from the anchor body for anchoring the anchor body and thereby also the vessel. Alternatively, the vessel may swivel around the anchoring system by the vessel being anchored via a mooring line to an anchored buoy. The vessel will then be able to pivot round the buoy. It will also be possible to fasten the vessel directly to an anchor on the seabed or ocean floor, in which case the vessel will be able to pivot round this point.
The vessel will advantageously be arranged in such a manner that it can be disconnected from the anchor as well as communication line(s), umbilical(s) and other devices connecting the vessel to the at least one well and the equipment disposed below the surface of the water. As mentioned above, this will be particularly advantageous where bad weather, possibly combined with a mishap or an accident, make it necessary for the said equipment to be disconnected from the vessel.
The means for producing energy on board the vessel may consist of at least one generator set. This may typically comprise a diesel engine or a gas turbine driving an electric generator. In this case the vessel will advantageously also include storage space for necessary fuel such as diesel or gas for operation of the at least one generator set. The vessel may advantageously be provided with two or more generator sets so that the vessel has at least one spare set in case a set breaks down.
The means for producing energy for operation of the at least one well and equipment disposed below the water surface may also comprise a small processing plant. In this case an appropriate amount of gas will be removed from the well stream and transferred to the vessel for processing. The vessel will then also be provided with at least one generator set for production of energy from the processed gas. As in the above case, the vessel will advantageously be provided with two or more generator sets in case operational problems should arise with one of the sets.
The vessel is furthermore advantageously provided with means for transferring the produced energy from the vessel to subsea equipment and possibly the at least one pipeline. This may involve a separate electric cable or an electric cable which is a part of an umbilical. If the energy transferred is in the form of hydraulic or pneumatic energy, these means could be a separate pipeline or a pipeline which is a part of an umbilical.
As mentioned earlier, parts of or all the equipment for energy production may be provided below the water surface instead of on the vessel.
A method is also provided for intervention on equipment in use in connection with production of hydrocarbons from at least one well and equipment for further transport of the well stream, where said equipment is disposed below a water surface, particularly on a seabed or ocean floor. The intervention is conducted from a vessel which is specially arranged for operation and maintenance of equipment disposed below the water surface. The vessel is provided with a system for anchoring, e.g. a mooring system, a dynamic positioning system or a combination of the two, where the anchoring system is arranged in such a manner that the vessel can rotate about or swivel round the anchoring system. The vessel is further provided with means for conducting an intervention on one or more intervention objects disposed below the water surface and preferably on the seabed or ocean floor, and means for lowering intervention equipment and possibly spare parts down to the intervention object or intervention objects. The method for conducting the intervention consists of the following steps:
When the operating and service vessel is positioned for lowering necessary tool systems and any spare parts for carrying out an intervention, underwater currents, for example, may make it necessary to position the vessel slightly to the side instead of being located vertically directly above the intervention object. The term “substantially above” should therefore be understood to mean that the vessel may be located slightly to the side relative to a vertical line from the intervention object if so dictated by the existing conditions.
An embodiment of the invention will now be described with reference to the figures, in which:
The ship is positioned in a suitable position relative to a subsea production system for oil and gas. The production system may be organised with one or more wells 24 with templates 34 with at least one integrated pressure booster unit 27 on each template or the well streams 25 may be collected in a central pressure booster station 35, where the pressure boosting is provided by at least one pressure booster unit 27, comprising one or more pumps or compressors. If necessary, several such pressure booster stations 35 may be provided. At the front edge of the at least one pressure booster unit 27, pre-processing means 26 may be provided for pre-processing the well stream and in the same way at the after edge of the at least one pressure booster unit 27, post-processing means 28 may be provided for post-processing the well stream. These pre- and post-processing means may, for example, be mixers, desanding equipment, water separation equipment and chemical injection equipment. The bottom-mounted equipment communicates with the ship through one or more risers 20 or umbilicals 21.
The vessel 10 is provided with at least one suitable power generating unit 14 which produces electric power and delivers it through the vessel's swivel system 13 and on through an electrical umbilical 22 to a termination point 30. If necessary, several electrical umbilicals 22 may be installed. At least one power regulating unit 15 may either be mounted on the vessel in its entirety, or the whole or parts of this at least one unit 15 may be mounted underwater in connection with associated power consumers such as pumps and compressors.
For operation of the vessel's at least one power generating unit 14, two possible solutions are suggested. The vessel 10 may carry the necessary fuel, such as, e.g., diesel, stored in separate fuel tanks 16 on the vessel. These tanks 16 may be refilled from other ships through a conventional transfer system. Alternatively, a small portion of the process flow, removed from the gas phase, may be passed up to the vessel 10 through a suitable riser 23. A compact little processing plant 36 pre-processes this gas flow so that it can be used as fuel in the power generating unit 14.
A processing plant of this kind may also be provided under water, preferably on the seabed. Parts of the processing plant may also be provided on the vessel while the rest is mounted under water. In order to ensure regularity and fuel during start-up and shutdown phases, it may also be expedient to have a compact little intermediate store 19 for gas. Alternatively, operating conditions of this kind may be met by supplying the power generating unit 14 with fuel from the ship's tanks 16. It may also be expedient to mount parts of or all the power generating equipment under water if public regulations or other legislation dictate that it is necessary.
In
Riser 56 and umbilical(s) 57 continue from the buoy 55 to the swivel 44 and from there on to subsea equipment such as a pressure booster station 35. In
The vessel 10 may be positioned in such a manner that by pivoting the vessel to given positions it can be employed as an intervention platform for subsea-mounted equipment such as, for example, a pressure booster station 35, i.e. the at least one pressure booster unit, pre- and post-processing means 26, 28, etc. as illustrated in
An important operation which can be conducted from the vessel 10 will be installation and operation of a subsea system for launching pigs. A pig is transferred from the vessel 10 to its subsea receiving station either in a tool 73 (
In addition to power generation and monitoring functions, in most cases it will be desirable to add chemicals to the well stream in order to safeguard the integrity of the pipe and an efficient flow (corrosion, wax and/or hydrate inhibitors) in the pipe system 32 to shore 33 where further processing will take place. These chemicals will advantageously be able to be stored in separate tanks 17 (
It may also be expedient, either under special conditions (for example at start-up), or on a permanent basis, to supply electric power through at least one heating means 31 (
The vessel 10 will also be a platform for necessary monitoring and control systems for parts of, or preferably all subsea-mounted equipment. This may be operated from onshore or locally from the vessel.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006 3352 | Jul 2006 | NO | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NO07/00273 | 7/19/2007 | WO | 00 | 9/29/2009 |
