Patent Grant
11970924
The present invention relates to a method of installing a subsea system comprising at least one compressor train. In addition, the invention relates to a subsea system comprising at least one compressor train.
In particular, the present invention relates to a method of operating a subsea system receiving a well flow stream from at least one upstream flowline and supplying the well flow stream to at least one downstream flowline at an increased pressure, where the compression capacity can be regulated during the lifetime of a field.
Gas handling is defined as one of the most important future business areas the oil and gas industry. As the undisputedly most efficient method to recover gas from subsea gas reservoirs, subsea compression plays a major role in the operator's gas handling strategy. To date two different subsea compression systems have been installed, one being Gullfaks SGC and the other Åsgard SGC. Both systems have two compressor trains at a common foundation. At Åsgard the second compressor train was installed on the same foundation structure as the first compressor train and put into operation one year after the first compressor train. The initial set foundation structure at Åsgard was therefore set with space for two compressor trains initially. However, both first and second installations consist of identical elements (inlet cooler, scrubber, compressor, pump and outlet cooler). A compression system designed for phased installation would today typically be similar to Åsgard, with a common foundation structure and with compression elements added at time of need or, alternatively, it would consist of several smaller compressor stations installed at different time and connected by spools at the seafloor.
The concept with common foundation structure is constrained by the following drawbacks:
The concept with multiple smaller compressor stations is constrained by the following drawbacks:
It is therefore a need to address the drawbacks related to the prior art solutions.
One of the objectives of the invention is to provide a cost-effective subsea solution where the compressor capacity can be increased during lifetime of the field, and where the investment related to added compression capacity is delayed to the time of need.
The invention is set forth in the independent claims, while the dependent claims describe other characteristics of the invention.
The invention provides a solution which delays the investment cost to the time of need and thereby improves the economy in the project (Net Present Value and Internal Rate of Return). Initially, a first compressor train comprising a flow conditioning unit, a compressor unit, a cooler and connection lines for subsequent second, third, . . . , xth compressor trains is installed. Then, as the reservoir is depleted and the pressure in the reservoir decreases, or if the well flow characteristics change and there is an increased demand of pressure assistance, additional compressor trains can be connected to the already installed compressor train(s). Therefore, according to the invention, as the need of compression may increase during lifetime of a field, a second (and possible additional) compressor train can be installed when required, by connecting this compressor train to the already installed compressor train(s). In order to simplify and ease installation as well as reducing cost, this second (and possible additional) compressor train does not have a dedicated flow conditioning unit. Instead of a flow conditioning unit, the second compressor train is either connected to an outlet of the first compressor via the connection lines (compressor trains in series), or alternatively, to an outlet of the flow conditioning unit of the initial compressor train via the connector lines (compressor trains in parallel).
Using relatively short horizontal spools between manifolds (e.g. piping) of the different compressor trains, it is possible to drain all liquid either to the inlet flowline or, more preferably, to the outlet flowline. If draining to inlet flowline, and the system comprises a flow conditioning unit, all of the drained liquid will enter the flow conditioning unit which will handle the liquid upstream the compressor(s).
The invention relates to a method of installing a subsea system comprising the steps of:
Each compressor train has at least one branch or connection line leading to the next compressor train and one connection line for receiving return fluid from the next compressor train.
The line at the position upstream of the first compressor can be the well flow line or a line from a flow conditioning unit. When using this line, parallel connection of the compressor trains can be obtained.
The first compressor train may be the only compressor train installed on the first foundation structure. In this example, the additional compressor train installed on the second foundation structure is a second compressor train. If two compressor trains are installed on the second foundation structure, these compressor trains are the second compressor train and the third compressor train, respectively.
Alternatively, the first compressor train and a second compressor train may be installed on the first foundation structure. In this example, the additional compressor train installed on the second foundation structure is a third compressor train. If two compressor trains are installed on the second foundation structure, these compressor trains are the third compressor train and the fourth compressor train, respectively.
One or more of first, second and/or third connection lines may either be connected separately to a subsequent compressor train, or they may be adjoined upstream of the connection to the subsequent compressor train.
The foundation structure for the “next compressor train” may be hung off in a connection interface on the foundation structure for the “previous compressor train”. Levelling and foundation elements will then only be required on the opposite side of the new foundation structure. The second foundation structure may comprise a complementary connection interface on the second foundation structure which mates with the connection interface of the first foundation structure. When connected, the connection interface and the complementary connection interface form a pivot connection between the first and second foundation structures such that the second foundation structure can be pivoted relative the first foundation structure and which supports the second foundation structure when positioned on the seabed. The connection between the connection interface and the complementary connection interface may be a hinged connection, a pivotally/pivotable joint or other suitable connections performing the required pivotability when connected.
The first installation, which comprises the first foundation structure and one or more compressor trains, shall preferably be arranged with all necessary arrangements for conditioning of the incoming hydrocarbon stream with respect to temperature-management (inlet cooler) and stabilization of liquid transients (Flow Conditioning Unit—FCU) if required. Any requirements for routing of flow between multiple inlet and outlet flowlines is preferably done in the first installation.
If a FCU is present, and in the event of high liquid/gas ratio, the liquid outlet of the FCU (in case of an FCU with separate liquid outlet) can be connected to a pump. If a pump is used, liquid will normally be pumped directly to the export field-flowline (i.e. the common outlet for the subsea system), and only gas will be routed to the next compressor train(s). The next compressor train(s) shall boost any flow coming from the compressed fluid line of the previous compressor train(s) without any further conditioning before entering the compressor(s) of the next compressor train(s). As such, all installations (i.e. second, third fourth, . . . , nth installation) after the first installation can be of similar and simplified design. It is also possible to design a system with both pump and feature(s) for injecting liquid into compressors (either via separate liquid lines or lines with a gas liquid mixture). Such system may enable boosting of liquid (by compressor) even in case the pump is not operating. Such system also enables compressor washing by process fluid in case of compressor fouling.
The common foundation structures supporting the different compressor trains of all installations are mechanically connected in the same plane (preferably in the horizontal or mainly horizontal plane) next to each other on the seabed. This facilitates interconnection of manifolds/piping of the different compressor trains and manifolds either by short horizontal spools or by skidding (i.e. horizontal movement) the components of the different compressor trains or manifolds into connection with each other avoiding spools resting on the seabed forming liquid traps. Skidding may be the preferred connection method if only 2 foundation structures shall be used. Spools may be the preferred connection method for a system that may be expanded to more than 2 foundation structures. If spools are used, they should preferably have a U-shape in the horizontal plane to obtain flexibility and drainage between compression trains.
The foundation elements supporting the foundation structures on the seabed can be mudmat(s), pile(s) or suction anchor(s), or combinations thereof. If using mudmat(s), the mudmat(s) are preferably connected to the foundation structure topside such that the foundation structure and mudmat(s) are installed together in one run. The same operation applies if using suction anchor(s) instead of mudmat(s) as foundation element(s). However, it is also possible to install the mudmat(s) or suction anchor(s) in one run, and thereafter install the foundation structure supported by the mudmat(s) or suction anchor(s).
A “next compressor train”, which could be the 2nd train, 3rd train, . . . nth train are connected to the “previous compressor train” (n-1) and will boost either the low pressure flow branched off from upstream the previous compressor or the high pressure flow branched off from downstream the (optional) previous discharge cooler (i.e. the previous compressed fluid line). As such the “next compressor train” can operate in series to or in parallel with the “previous compressor train(s)”. The discharge of each compressor train can either be routed to the next compressor train for further boosting or back through the previous compressor train(s) into the well flow line. It is envisaged that all “next compressor trains” are of identical design (possibly except for compressor aerodynamic bundle in series operation).
For each train, all separate retrievable modules may be connected directly to the manifold, either by horizontal skidding or vertical connections.
The process system of the “next compressor train” may be coupled to the “previous compressor train(s)” via the manifolds. Manifolds can be interconnected by skidding or by use of short spools, avoiding any pipe elements on the seafloor. This will allow any liquid in each of the compressor trains to be drained to the well flow line (or the common outlet for the subsea system) prior to start. With interconnecting spools at seafloor any liquid would accumulate in these spools and cause startup-challenges of the compressors.
The method may further comprise a step of connecting a flow conditioning unit to the at least one well flow line upstream of the inlet of the first compressor.
The flow conditioning unit may:
A flow conditioning unit may not be needed if gas flow is relatively dry and without liquid slugs or surges.
The method may further comprise the steps of:
The method may further comprise the steps of:
One possible solution is to have a combined outlet/anti-surge cooler (anti-surge=recycle) at each compressor train. In series operation the outlet cooler of train n will then act as inlet cooler to train n+1. In case of high gas temperature at wellstream entering the first compressor train an additional inlet cooler may be placed at the inlet of the first compressor train upstream the branch-off to the next compressor train (and thereby provide cooled gas to all compressors in parallel operation).
The method may further comprise a step of:
The method may further comprise a step of:
The method may further comprise the steps of:
The second compressor train may, if required, comprise a second cooler. In addition, the second compressor train may comprise a connection interface connectable to a third foundation structure.
The method may further comprise moving or skidding components forming part of the subsea system into position relative each other on the common foundation structure.
The method may further comprise installing a second compressor train on the first foundation structure.
The method may further comprise:
The method may further comprise the steps of:
The connection of the second compressor train, i.e. the additional compressor train, may comprise, in order to arrange the first and second compressor trains in series, the steps of:
The connection of the second compressor train, i.e. the additional compressor train, may further comprise, in order to arrange the first and second compressor trains in parallel, the steps of:
The method may further comprise:
Each of the foundation structures may comprise one common manifold for all of the compressor train(s) on that foundation structure. For example, if the first foundation structure only has one compressor train, i.e. the first compressor train, installed thereon, the manifold serves this one compressor train. In another example, if there are two compressor trains, i.e. the first and a second compressor train, installed on the first foundation structure, the manifold is common or shared by both of these compressor trains. Similarly, if the second foundation structure only has one compressor train installed thereon, the manifold is dedicated for this one compressor train. In another example, if two compressor trains are installed on the second foundation structure, the manifold is common or shared by both of these compressor trains.
The skilled person will understand that the flow conditioning unit may comprise two or more outlets arranged next to each other for connection to the fluid lines leading to the first and second compressors to ensure similar flow characteristics in the different fluid lines. This may be done by connecting separate gas and liquid lines to each new compressor train, with a valve device, so that liquid is injected in a controlled manner into the gas line directly upstream each compressor. A second alternative is to have one common outlet for lighter and heavier fluid lines from the flow conditioning unit where the common outlets are connected to a pipe with two or more branch connection lines (such as Y or T connections or even more branches). A third alternative is to have one sole outlet from the FCU, where mixing of gas and liquid is performed internally in the FCU, and where mixed gas and liquid exits through the same sole outlet. A flow regulation device can be arranged in the sole outlet, which flow regulation device can be operated to adjust the amount of mixed gas exiting the FCU and entering the compressor(s).
Although each compressor train has one branch or connection line leading to the next compressor train and one connection line for receiving return fluids from the next compressor train, the first compressor phase may account for and prepare the possibility of connecting more branches later during the lifetime of the field. The branch(es) not used in the first compressor train may then be provided with a valve device which is closed until the second, or any additional compressor train(s), is installed.
When these second or additional compressor trains is installed, the valve device is opened allowing fluid to flow through the branch to compressor(s) in later installation phases. For example, in parallel operation with two compressors, two valves in the heavier fluid line shall be controlled to 50% flow in both liquid lines. In case of three compressors, one valve in the heavier fluid line leading to the first compressor is controlled to ⅓ liquid flow, while the other valve in the heavier fluid line leading to the second and third compressors are controlled to ⅔ liquid flow. Any T-branches in the line at second train shall ensure that liquid/gas mixture is equal in each branch. Each train shall preferably have a T-branch so that the same flow-spilt functionality is maintained if a next compressor train is connected. A third alternative is to install a pump at the first compressor train pumping liquid directly from the FCU (or scrubber) to the common outlet of the system. In this solution, dry gas (or almost dry gas) flows from the first compressor train to the next compressor train(s).
It is further described a subsea system comprising:
Similarly as for the method, the first compressor train may be the only compressor train installed on the first foundation structure. In this example, the additional compressor train installed on the second foundation structure is a second compressor train. If two compressor trains are installed on the second foundation structure, these compressor trains are the second compressor train and the third compressor train, respectively.
Alternatively, the first compressor train and a second compressor train may be installed on the first foundation structure. In this example, the additional compressor train installed on the second foundation structure is a third compressor train. If two compressor trains are installed on the second foundation structure, these compressor trains are the third compressor train and the fourth compressor train, respectively.
The first compressor train may comprise a flow conditioning unit connected to the well flow line, and the flow conditioning unit may comprise at least a first outlet connectable to the inlet of the first compressor via at least one fluid line.
The line at the position upstream of the first compressor can be the well flow line or a line from a flow conditioning unit. When using this line, parallel connection of the compressor trains can be obtained.
The subsea system may comprise a first cooler upstream and/or downstream of the first compressor. The cooler may be upstream of the first compressor, but more preferably downstream of the first compressor either in the first compressed fluid line or in the common outlet for the subsea system (or both).
The subsea system may further comprise:
The additional compressor train, i.e. the second compressor train, may comprise a second cooler. The second cooler is preferably arranged in the second compressed fluid line.
In an aspect, the components required for the second and any later foundation structures and compressor trains are identical.
In an aspect, the subsea system further comprises other necessary equipment for operating components of the subsea system, wherein said equipment is located at the same foundation structure as the compressor train it shall operate, such as e.g. power equipment for operating the first compressor can be located on the first foundation structure.
At least some of the components forming part of the subsea system may be movable or skiddable on the common foundation structure, such that the subsea components can be arranged closed relative each other.
The subsea system may further comprise:
In an aspect of the subsea system, the fluid line connecting the at least first outlet with the first compressor may comprise a first recycle line recycling fluids through the first compressor, and wherein the first recycle line may comprise a first anti-surge valve.
It is obvious that instead of a subsea system comprising compressor trains, the setup described herein will be appropriate for a subsea system comprising pump trains. The components forming part of such a subsea system with pump trains will be similar as the ones described herein (except for the more compressor and pump specific components).
Summarized, the method and system according to the invention described herein have the following main benefits:
In addition, the long spools between a first and second compressor train of prior art solutions are superfluous because the foundation structures are connected directly to each other forming a common foundation structure. As such, the different compressor trains are supported on the common foundation structure meaning that the different compressor trains will not move relative each other. This results in that smaller spools or direct pipelines can be used for connecting up the compressor trains.
These and other embodiments of the present invention will be apparent from the attached drawings, where:
In the following, embodiments of the invention will be discussed in more detail with reference to the appended drawings. It should be understood, however, that the drawings are not intended to limit the invention to the subject-matter depicted in the drawings. Furthermore, even though some of the features are described in relation to the subsea system only, it is apparent that they are valid for the related method as well, and vice versa. Hence, any features described in relation to the method are also valid for the subsea system.
Furthermore, in the following specific description, reference is made to a first connection line, a second connection line and a third connection line. The first connection line (10′,10″,10′″) is described in relation to series operation of compressor trains, while the second connection line (11′, 11″, 11′″) is the same return line both for series and parallel operation of the compressor trains, and the third connection line (12′,12″,12′″) is described in relation to parallel operation of the compressor trains.
It is clear that in simplest form, the subsea system only requires either:
In
On the right-hand side in
In
In
In
In
In
The second compressor train is preferably prepared for connection with a third compressor train in the event even further compression is required during the lifetime of the field. The installation of a third, and possibly an additional fourth, fifth, sixth, . . . , tenth) compressor trains, is performed similarly as described with reference to
In particular, the subsea system 1 in
The main difference between the first foundation structures 13′ in
The second foundation structures 13″ comprises a complementary connection interface 51′ for connection to the connection interface 50′ on the first foundation structure 13′ and required pipes for each compressor train (referred to as reference number 27″). The difference between the second foundation structures 13″ in
In particular,
It is further disclosed a (third) connection line 12′ connected to the fluid line 6″ for parallel connection of the first compressor train with the second compressor train. The third connection line 12′ comprises a flow regulation device 22′.
The compressed fluid line comprises a flow regulation device 24′ downstream of the first cooler 30′ and the connection to the first recycle line 40′. A first connection line 10′ for connecting the first compressor train with the second compressor train is connected to the first compressed fluid line 9′ upstream of the flow regulation device 24′ and downstream of the first cooler 30′ and the connection to the first recycle line 40′. The first connection line 10′ comprises a flow regulation device 20′ which is closed when no additional compressor trains are connected. A second connection line 11′ for connecting the first compressor train with the second compressor train is connected to the first compressed fluid line 9′ downstream of the flow regulation device 24′ and upstream of the common outlet 16 for the compressed fluid in the subsea system 1. The second connection line 11′ comprises a flow regulation device 21′ which is closed when no additional compressor trains are connected.
A second compressed fluid line 9″ is connected to an outlet 15″ of the second compressor 8″ in one end thereof and to a common outlet 16 for the compressed fluid in the subsea system 1 in a second end thereof. The second compressed fluid line 9″ comprises a second cooler 30″. A second recycle line 40″ with a second recycle valve 41″ (regulated type) ensuring a minimum allowed flow in the second compressor 8″ and the second cooler 30″ extends from first connection line 10′ upstream of the second compressor 8″ to the second compressed fluid line 9″ downstream of the second cooler 30″. The second compressed fluid line 9″ comprises a flow regulation device 24″ downstream of the second cooler 30″ and the connection to the second recycle line 40″. A first connection line 10″ for connecting the second compressor train with a third compressor train is connected to the second compressed fluid line 9″ upstream of the flow regulation device 24″ and downstream of the second cooler 30″ and the connection to the second recycle line 40″. The first connection line 10″ comprises a flow regulation device 20″ which is closed when no additional compressor trains are connected. A second connection line 11″ for connecting the second compressor train with a third compressor train is connected to the second compressed fluid line 9″ downstream of the flow regulation device 24″ and upstream of the common outlet 16 for the compressed fluid in the subsea system 1. The second connection line 11″ comprises a flow regulation device 21″ which is closed when no additional compressor trains are connected.
In order to ensure that the same well fluid is compressed both in the first compressor 8′ in the first compressor train and the second compressor 8″ in the second compressor train, the flow regulation device 24′ in the first compressed fluid line 9′ is closed such that compressed well fluids in the first compressed fluid line 9′ is directed to the inlet 14″ of the second compressor 8′ (except any fluid directed through the first and/or second recycle line 40′, 40″) and exit the subsea system through the common outlet 16.
Series operation of the first and second compressors 8′, 8″ in the first and second compressor trains, respectively, can be achieved by operating the following valves to be in a closed or an open position:
The flow regulation devices 42′, 42″ in the fluid lines 7′,7″ for heavier fluids may be open or closed dependent on the characteristics of the fluid from the well flow.
The fluid flow through the first compressor train and further through the second compressor train is indicated by the thick solid line in
Parallel operation of the first and second compressors 8′, 8″ in the first and second compressor trains, respectively, can be achieved by operating the following valves to be in a closed or an open position:
The fluid flow through the first compressor train is indicated by the thick solid line in
A third compressed fluid line 9′″ is connected to an outlet 15′″ of the third compressor 8′″ in one end thereof and to a common outlet 16 for the compressed fluid in the subsea system 1 in a second end thereof. The third compressed fluid line 9′″ comprises a third cooler 30′″. A third recycle line 40′″ with a third recycle valve 41′″ ensuring a minimum allowed flow in the third compressor 8′″ and the third cooler 30′″ extends from first connection line 10″ upstream of the third compressor 8′″ to the third compressed fluid line 9′″ downstream of the third cooler 30′″. The third compressed fluid line 9′″ comprises a flow regulation device 24′″ downstream of the third cooler 30′″ and the connection to the third recycle line 40′″. A first connection line 10′″ for connecting the third compressor train with a fourth compressor train is connected to the third compressed fluid line 9′″ upstream of the flow regulation device 24′″ and downstream of the third cooler 30′″ and the connection to the third recycle line 40′″. The first connection line 10′″ comprises a flow regulation device 20′″ which is closed when no additional compressor trains are connected. A second connection line 11′″ for connecting the third compressor train with a fourth compressor train is connected to the third compressed fluid line 9′″ downstream of the flow regulation device 24′″ and upstream of the common outlet 16 for the compressed fluid in the subsea system 1. The second connection line 11′″ comprises a flow regulation device 21′″ which is closed when no additional compressor trains are connected. A third connection line 12′″ for connecting the third compressor train with a fourth compressor train is connected to the fluid line 6′″ for lighter fluids. The third connection line 12′″ comprises a flow regulation device 22′″ which is closed when no additional compressor trains are connected.
The remaining components forming part of the first and second compressor trains are similar to the setup described with reference to
Parallel operation of the first, second and third compressors 8′, 8″, 8′″ in the first, second and third compressor trains, respectively, can be achieved by operating the following valves to be in a closed or an open position:
The fluid flow through the first compressor train is indicated by the thick solid line in
The invention is now explained with reference to non-limiting embodiments. However, a skilled person will understand that there may be made alternations and modifications to the embodiment that are within the scope of the invention as defined in the attached claims. For example, if the well flow is mainly liquid, pump trains may be set up in a similar manner as the compressor trains as described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20200357 | Mar 2020 | NO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/057751 | 3/25/2021 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2021/191354 | 9/30/2021 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20070029091 | Stinessen | Feb 2007 | A1 |
| 20090200035 | Bjerkreim | Aug 2009 | A1 |
| 20120118008 | Dam et al. | May 2012 | A1 |
| 20150104328 | Babbitt et al. | Apr 2015 | A1 |
| 20150184490 | Kanstad | Jul 2015 | A1 |
| 20170159421 | Sillapacharn et al. | Jun 2017 | A1 |
| 20190360313 | Ellingsen et al. | Nov 2019 | A1 |
| Number | Date | Country |
|---|---|---|
| 20151447 | Nov 2016 | NO |
| WO 9606260 | Feb 1996 | WO |
| WO 2019076580 | Apr 2019 | WO |
| WO 2019209119 | Oct 2019 | WO |
| WO 2020002215 | Jan 2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20230107601 A1 | Apr 2023 | US |
