WO2004085789A2 - Well system, unit module and method for formation of a well system - Google Patents

Abstract

The invention relates to a well system, comprising at least one well (4) with a well tree (5) and a receiving station for well fluids produced by the well (4). The well (4) and the receiving station are arranged at a distance apart corresponding to a multiple of a unit distance and the connection between them is composed of at least one unit module with a length corresponding to a multiple of the unit distance. The invention also relates to a unit module for use in the well system and a method for formation of the well system.

Description

Well system

The present invention relates to a well system where at least one well is connected to a receiving station for fluids produced by the well, a unit module for use in the well system and a method for formation of a well system. Today's subsea developments fall into roughly two categories. In a so-called "template" solution a foundation frame is employed on which the manifold is mounted and which in addition has guides for a number of wells, normally four or six. The manifold in the middle is arranged for collecting hydrocarbons produced from the wells and dispatching them to a remote location. An example of such a solution is disclosed in NO patent no. 309620. An advantage of this solution is that the distance between well and manifold is predetermined, thus simplifying the manufacture of the connections between well and manifold. In addition this is a compact and relatively inexpensive solution, which has been used in many places around the world. The disadvantage of this solution is that the close proximity between the wells leads to a greater risk of pieces of equipment coming into conflict with or colliding with one another during installation or well overhauling operations. Many oil companies therefore demand that all the wells on the template must be closed down if work is to be carried out on one of the wells. Another drawback may be washout problems which may entail the need for expensive foundation work. A further drawback is that it provides little room for effective modularisation, e.g. in order to include process equipment, flexibility in pipe coils, etc.

In a so-called "satellite" or "cluster" solution the manifold is mounted on a separate foundation and a number of wells located at an arbitrary distance from the manifold. The advantage of this method is that the wells can be placed at a safe distance from one another, thereby reducing washout problems and interference. Locating the well sites, however, becomes more arbitrary and there is limited or no control over the distance between well and manifold. The pipe connections between well and manifold therefore have to be tailored to suit each individual case according to position measurements made on the seabed. The result is that the "spools" or "jumpers" have to be prepared as a part of the offshore installation operations, which entails extra costs. The alternative is to manufacture them in a workshop, but this entails longer transport and delivery times, thus also increasing the costs.

The common feature of both the known solutions is that the well stream from several wells is mixed in the centrally located manifold. This means that the flow pressure from each well has to be equalized in order to avoid kick. In practice pressure reducing valves are provided on every well and the pressure is reduced to the pressure from the lowest well. This may, for example, involve setting up a booster pump downstream of the manifold in order to provide sufficiently high pressure to enable the flow to be passed up to the platform. It will be appreciated that this results in extra problems and increased costs since wells with sufficiently high pressure first have to undergo a pressure reduction and subsequently a pressure increase at other points in the system. If a process plant is to be employed on the seabed, at present this is usually located downstream of the manifold. This makes separation more difficult and offers little flexibility with regard to alterations over the life of the field. It has also been proposed to place the process plant down in the well, but such solutions are technically highly complicated and so far have not been applied. By establishing a system for controlling well locations relative to a reference point on the manifold centre, or establishing a reference point relative to a well so as to determine distance and tolerances between well and manifold, it becomes possible to prefabricate the pipe connections (spool or jumper) interconnecting each well with the manifold centre, thereby achieving great savings. In a system of this kind the wells can be located relatively close to the manifold, but at a safe distance from it and the conditions can be arranged so that the distance between each individual well and the manifold is substantially identical within given tolerance limits. The increased distance between the wells provides more freedom for optimal positioning based on reservoir conditions. It also reduces the risk of washout between the wells. Another advantage is that wells can be put into production while the adjacent wells are being drilled (provided the manifold is in position), which in turn results in better capital flow in the development phase.

Systems for controlling the well location relative to manifold centre may be based on mechanical/physical guides installed as a temporary or permanent part of the plant. In this case the system can be designed so that it also acts as a foundation for wells and manifold. Alternatively, the well location may be controlled by means of hydroacoustic systems with networks of transmitters and receivers that directly indicate the exact position of drilling bit/well location.

Previously known solutions which aim to establish a well according to a reference point have many disadvantages. In US patent publication no. 4.317.488, for example, a fixed point is established on the seabed, whereupon a spacer is lowered. One end of the spacer is secured to the centre point while the other end has guides for controlling the drilling of a well. This solution is employed only for establishing the position of the wells and for enabling standard pipe lengths to be manufactured for well fluids and hydraulic lines and offers no possibility of integrating process modules. In Norwegian patent application no. 20012603 another method is illustrated and described for establishing spacing between a well and a reference point. It is proposed herein that a structure, manifold or pipeline is placed on the seabed and a spool of fixed length is attached at one end to the structure, whereupon the other end serves as a template for drilling a well. The drawback with this is that first of all the manifold or the pipeline has to be positioned in advance, which is undesirable from a cost point of view. Another drawback is that the spool has little flexibility, particularly in the vertical direction, thus making the connection between well and spool highly complicated. In NO patent publication no. 177.915 a method is described where on the manifold flexible hoses are rolled up which are already coupled up to the manifold and which can be withdrawn from connection with the well after the well has been drilled and completed. However, this gives an extremely heavy and expensive manifold. Here too another disadvantage is that the manifold has to be completed in advance, nor does it provide any possibility of integrating process modules in the connection.

An object of the present invention is to provide an improved well system compared to today's existing solutions as described above.

This object is achieved with a well system, a unit module and a method for formation of a well system as indicated in the following claims.

The present invention attempts to provide a system which, establishes a distance between the subsea installations as a multiple of a unit distance, thereby permitting standardised connections, unit modules, to be used between the individual subsea installations. An example of such a connection is that which has to be established between each wellhead Christmas tree and the central manifold or header.

Such a system according to the present invention will make it possible to prefabricate the connections within the tolerance limits specified. The connection can also be made easily replaceable. It can be guided into position between the well tree and the manifold without guidelines to the surface and is therefore suitable for use in deep water. The connection points may be horizontal or vertical. A vertical connection is simpler but has the disadvantage that the connection has to be removed if the well tree or manifold have to be replaced. In this case, however, a "parking space" can be provided on the seabed for temporary placement of the connection. In the case of a horizontal connection, the connection has to be supported on the seabed, but this can be done by means of known per se methods such as "mud mats" or guide bases. In an embodiment of the invention the well system is established by means of an inflatable concrete foundation which has fixed points for supporting the connections.

The standardised connection is advantageously mounted in a box or frame for easier handling and in order thereby to protect the parts against damage from fishing tackle (trawlers or the like). Since it has standard physical measurements ("envelope"), i.e. length, height and width, the equipment that may form part of the connection may also have a fixed position and orientation. Thus equipment parts can also be standardised and easily replaced as required. An example of this kind of standard equipment is choke valves which are normally necessary during an initial part of the well's life cycle, while later there may be a need for a process module since the well has begun to produce water. This process equipment will typically comprise pumps, separators, power distribution, choke valves, control valves, hydrocyclones, compressors, sand removal equipment, injection valves, etc. The connection is designed so that the process equipment can be included, preferably without changing the pipe arrangement.

The system also permits some of the well equipment to be placed on the connections, which in turn will help to simplify the well installation, i.e. the well tree. For example, the weight of well trees is a critical parameter due to limitations in connection with transport, and the invention makes it possible to simplify the well tree (thereby reducing the weight) by transferring functions, which at present are located on the well tree, to the connector. This applies particularly to the choke valve, but some measuring instruments such as multiphase meters, pressure and temperature gauges and other equipment such as the control module and chemical injection valves can also be placed on the module.

Even though the connection is primarily intended for use in a "cluster" system, i.e. a collection of wells, the wells may alternatively be located in a row where the wells are optimally placed along a pipeline. Since the standard connections can be equipped with an integrated process system, the production can be conveyed directly into an export pipeline without the use of a manifold. Alternatively, the manifold may be integrated in the end of the pipeline, a so-called PLEM ("PipeLine End Manifold").

Thus the invention permits an increased modularisation and simplification of the installations on the seabed. By employing a foundation system whose dimensions are fixed relative to one another, the object is achieved that the distances between the various installations are predetermined and since the deviations are known, the tolerances are also known. The system can therefore be used to control well locations relative to a reference point established at a point on the foundation, for example relative to the centre of a well. The distance between a well and a manifold is thereby established so that distance and tolerances permit prefabrication of the elements connecting the two installations. This means that the connecting elements can be prefabricated, thus providing increased modularisation.

The combination of foundation and connections permits increased spacing between the wells compared to today's template-based solutions and will be a better solution than today's satellite solutions.

The flexibility in the module can be provided in different ways. A steel tube may be employed with a geometry that provides the desired flexibility, a flexible hose, a combination of steel tube and hose or a steel tube which has flexible end pieces, i.e. spirals, telescopic parts, swivel joints or the like. The position of the end pieces in the module, however, is fixed and thereby known relative to the point with which the module is to be connected. Thus elements such as pressure reducing valves, pumps, etc. can be placed between the fixed points without changing the defined end geometry.

The invention also permits the use of an integrated trawl protection on the different parts of the installation. Since the height can be reduced and there is no need to make room for BOP as in today's systems, this makes the trawl protection cost- effective compared to typical present day trawl protection systems. The invention will now be described in greater detail with reference to the accompanying drawings, in which: figs. 1-4 illustrate examples of module types.

Figs. 5-9 are schematic flow diagrams for different module types.

Figs. 10-12 illustrate sections of a single connection module. Fig. 13 is a drawing of a process module.

Figs. 14-17 illustrate examples of process variants.

Fig. 18 illustrates a subsea foundation for use together with the invention.

Fig. 19 illustrates a second subsea foundation for use together with the invention.

Fig. 20 illustrates the foundation in fig. 18 extended with modules. Fig. 21 is a detail of fig. 20.

Fig. 22 illustrates a trawl protection for the foundation according to fig 18.

Fig. 23 illustrates a third subsea foundation for use together with the invention.

In figs. 1-9 identical or corresponding parts are indicated by the same numerical reference. Figs. 1-4 illustrate examples of module types according to the invention. All the modules are of standard size and are mainly composed of the same component types where the different functions are provided by devices placed inside the module's outer frames. Each module therefore comprises a frame 11 consisting of a number of horizontal and vertical structural frame parts, such as U-beams, H-beams, etc. which are commonly known to a person skilled in the art. The frame forms attachment points for the different process parts incorporated in the module. All the modules have two pipe connectors 12 and 13 respectively attached to the frame intended for connection with a well and a receiving station, which is preferably a manifold but which may also be a pipeline. Between the pipe connectors 12, 13 there extends a pipe 14. The pipe 14 is provided with a flexible portion, thus enabling it to absorb tolerance stresses produced during tie-in on the seabed or from temperature changes. In one embodiment the pipe has a double U-shape (see figs. 10 and 1 1). In a second embodiment the pipe may be in the form of a spiral (see fig. 12). Alternatively, the connection between the pipe 14 and the connector may be telescopic. The manifold's connector 8 (see fig. 10) preferably has several channels and is therefore prepared to be interconnected with modules with multi-channel connectors 13. This increases the flexibility and permits modules to be replaced during the life of the well. The modules are preferably equipped with a roof 18 as illustrated to provide protection against falling objects or trawl boards.

A number of different module types will now be described with reference to figs. 5- 9 which depict flow diagrams for a selection of module types. Fig. 5 illustrates a pressure limiting module 10, also illustrated in fig 1, comprising a first pipe 14 connected to the connector 12 and a second pipe 16 connected to the connector 13. A choke valve 15 is inserted between the pipes 14 and 16 in order to reduce the pressure of the fluid flow to the manifold. A connecting unit 17 may be mounted on the frame for connecting signal cables, hydraulic lines or power supply.

In a "template" or "cluster" development, fluid is supplied from several wells to a collecting manifold. The fluid flowing from the wells to the manifold must have approximately the same pressure and the pressure limiters on the wells are arranged to reduce the pressure in the wells with the highest pressure to the pressure of the well with the lowest pressure. This is a standard technique in subsea developments. A significant advantage of standardised modules according to the invention is that the choke valve can be placed on the module for increased flexibility.

Fig. 6 illustrates a booster module 20, which is also illustrated in fig. 2. As in the above, it comprises a first pipe 24 connected with the connector 12 and a second pipe 26 connected with the connector 13. Between the pipes a pump unit 21 is inserted. The pump unit comprises a first loop 22 with a pump 29 and a stop valve 22a and a second loop 23 with a stop valve 23a that acts as a bypass to allow fluid to pass the pump if necessary. The valve 23a is normally closed. A choke valve 15 is also illustrated but will normally be omitted in this case. An electric connector 28 coupled to an external power supply 27 supplies the pump with current.

A producing well will normally have a high initial pressure which gradually decreases in the course of its life. As mentioned above it is important for the fluids to the manifold to have equal pressure. When the pressure in one well drops below the pressure in the other wells, it will normally be necessary to reduce the pressure in the other wells to the lowest pressure. This is far from advantageous since energy is thereby removed from the well stream which in the next phase is used to pass produced oil to a platform. In such cases, with the modules in the invention the module in the well with the lowest pressure (the pressure limiting module 10) can be replaced by the module 20, thereby increasing the resultant pressure in the production pipeline. Fig. 7 illustrates a water separator module 30, also illustrated in fig. 3. As in the above, it comprises a first pipe 34 connected to the connector 12 and a second pipe 36 connected to the connector 13. The pipe 34 is connected to a water separator 31. The water separator comprises in the commonly known manner a tank where oil and water are separated on account of their different specific gravities. In order to increase the efficiency of the separation process, an electric field can be established in the separator, or introduced into a separate unit. The oil is removed in a pipe 32 which in turn is connected to the pipe 36. A pump unit 21 may be connected between the pipes 32 and 36 in order to increase the pressure in the oil flow. The water is removed in a pipe 33 and connected to an external pipeline 35 to be conveyed to an injection well 34. Alternatively, the separated water may be passed in a pipe (not shown) to the pipe connector 13 and on to the manifold where it is mixed with any water separated from other wells, thus enabling collected separated water to be dispatched to a remote location or to a platform.

A producing well will normally contain increasing amounts of water in the course of its life. With the module system according to the invention the costs of installing expensive separation equipment can be postponed until the need arises. When the proportion of water reaches an upper limit, therefore, the original simple module (for example the module 10) can be replaced by the module with a water separator without the necessity of further modifications to the well or manifold. Fig. 8 illustrates a gas/liquid separator module 40. It comprises a first pipe 44 connected to the connector 12 and second 46 and third 45 pipes respectively connected to the connector 13. The pipe 44 is connected to a degasser 41. It comprises a tank for gravity separation of gas and liquid (oil and any water). The gas is removed in a pipe 42 and possibly via a choke valve 43 to the pipe 45. The liquid is removed in a pipe 43 which is connected to the pipe 46. In the same way as above, a pump unit 21 may be connected between the pipes 43 and 46 to increase the pressure in the liquid flow. The connector 13 is in the form of a multi-channel connector with two channels. Since the corresponding connector on the manifold, as described earlier, has corresponding channels, gas and oil from several wells can be collected in the manifold for further transfer to separate pipelines.

Fig. 9 illustrates a three-phase separation module 50. It comprises a first pipe 54 connected to the connector 12 and second 56 and third 55 pipes respectively connected to the connector 13. The pipe 54 is connected to a three-phase separator 51. It comprises a tank for gravity separation of gas, oil and water. The gas is removed in a pipe 52 which is connected to the pipe 55. A choke valve may be connected between the pipes 52 and 55. The oil is removed in a pipe 53 which is connected to the pipe 56. A pump unit 21 may be connected between the pipes 53 and 56 to increase the pressure in the oil flow. The water, together with any accompanying sand, is removed in the pipe 57 and connected to an external pipeline 34 for transfer to an injection well. Alternatively, the separated water may be conveyed in a pipe (not shown) leading to a third channel in the pipe connector 13 and thereby on to the manifold, where it is mixed with any separated water from other wells, thus enabling collected separated water to be dispatched to a remote location or to a platform. However, this requires the manifold to be prepared for this by the receiving connector having more than two channels.

A well, which at the beginning of its life produces gas and oil, will normally later also begin to produce water. The amount of water usually increases with time. With the modules according to the invention a two-phase module (degasser) can be provided at the start of the production. As the amount of produced water exceeds a specific amount, the module can be replaced by a three-phase module.

The flexibility and replaceability of the modules is dependent on the ability to provide a standard spacing between well and manifold, thus giving the modules a standard size within the tolerances that are desirable. Examples of equipment for establishing wells and manifold centres on the seabed so as to achieve this will be described later with reference to figures 16-18.

Figs. 10-12 show an example of a connecting module (an example is also illustrated in fig. 1), illustrating the design of the pipes so as to obtain the desired flexibility. As shown here, the connector 12 is intended to be connected to a corresponding connector 9 mounted on a well (see fig. 16). From the connector 12 the pipe 16 extends in a first horizontal part, followed by a vertical U. As can be seen in fig. 11 the lower part of the U is also formed as a horizontal U. The connector 13 is intended to be connected to a corresponding connector 8 mounted on a manifold (fig 16) or a pipeline (fig. 17). The manifold connector 8 has several channels, in the drawing two are shown, 8a and 8b. In the example the connector 13 is also equipped with two channels 13a and 13b, but since for this module there is no need for channel 13b, it is only connected to a pipe socket 16a which is not in use. As mentioned earlier, this is advantageous since the module can be replaced by another module, such as a separation module, where use is made of both channels 13a, 13b. The spool also comprises a choke valve 15 inserted between the pipes 14 and 16, as described earlier. The choke valve may be integrated in the jumper module or more advantageously designed as a separate retrievable unit for replacement or overhauling. The frame 1 1 comprises attachment points 61 for wires 62, thus enabling the module to be installed by means of a crane and wire or chain. Fig. 14 illustrates an example of a spiral pipe. Such a shape makes it easier to absorb stresses in the pipe but is more expensive to manufacture.

Fig. 13 depicts a drawing of a water separation module 30. The numerical references in this figure are identical to fig. 7, to which reference should therefore be made for an explanation of the figure.

Figs. 14-17 are schematic illustrations of different embodiments of modules comprising a separator, illustrated in the example as a gas/oil separator as schematically illustrated in fig. 8. The separator is designed as a tubular tank where gas and oil are separated on account of their different specific gravities. A major advantage of the invention is that when the separator is provided in connection with the well (each well has its own separator), the tank can be made smaller in size and it can be adapted to suit the requirement, i.e. the fluid composition of the individual well.

In fig. 14 the tank is a spiral pipe. By performing separation in a pipe, a more efficient separation is obtained. The different fluids have a shorter distance to the separation layer. A shorter distance gives a shorter separation time. In addition, the area of the separation layer is relatively large compared to the separator volume, with the result that multiple dispersions (drops in drops) are diffracted relatively quickly by sheer forces in the separation layer. Faster separation reduces the residence time requirement, thereby permitting less separator volume. The spiral pipe may also reduce the need for other devices for absorption of tolerances, since these are absorbed in the spiral.

Figs. 15 and 16 are identical, the separator being provided in the form of a number of tubular tanks arranged in parallel. The tanks are advantageously arranged in groups, for example, as illustrated in fig. 15, a first group of two tanks and a second group of three tanks. This provides greater flexibility in relation to the amount that has to be separated, since use may be made of one or both of the groups. In fig. 15 only the second group is in use. It should be understood that the design depicted in the drawings is only intended as an example, as the tanks may be grouped in any manner whatever and the number of tanks may be more or less than five, within the dimensions permitted by the module. The tanks may also be individually controlled. As described earlier, the module comprises two connectors 12 and 13 for connection to well and manifold respectively. The well flow is conveyed in the pipe 14 and into the tank(s). The gas is separated at the top, then removed and conveyed in the pipe 142 to the connector's 13 channel 13a and on through the channel 8a to the manifold, while the oil is passed in the pipe 143 to the connector's 13 second channel 13b (fig. 10) and on through the channel 8b to the manifold. In the manifold the flows from several wells are collected and dispatched to various plants for further processing. In fig 16 the tubular tanks are arranged at an angle relative to a horizontal line. In some cases this will give better separation.

In fig. 17 the tubular tanks are arranged in series so that the flows are passed from one tank to another. This gives longer residence in the tank and may result in better separation.

When the module is employed together with the foundation illustrated in fig. 18, a guide pin 160 (fig. 17) may advantageously be provided to guide the module down on to a foundation pad 125, as illustrated by dotted lines in fig. 17.

Fig. 18 illustrates a subsea foundation 1 which is suitable for use together with the invention. The foundation is made of a flexible material which, when filled with hardenable material, expands into the form illustrated in fig. 18. It consists of a number of pads 125 which can be combined with one another in such a manner that uniform building blocks are formed. The building blocks in turn can be combined in different ways to form a foundation for a desired number of wells. Thus the example in fig. 18 shows a rectangular foundation adapted for a development with four wells, one in each corner, with a centrally located manifold, composed of four building blocks 112 and one building block 111.

A suitable size for such a building block is three times the pad's length in the longitudinal direction and one pad length in width (this is not shown in the drawings). For example, if each pad is 5 x 5 metres, each module unit will be 5 x 15 metres. This gives a standard spacing between the wells of approximately 10 metres, which is advantageous from the safety point of view. When, as illustrated in fig. 18, an additional building block 112 is provided as a transition piece between the well foundations 112 and the middle manifold foundation 111, it gives the same spacing of 10 metres between the wells in the corners and between a well installation and the manifold in the middle. They therefore act as spacers but may if so desired be employed for installation and support of equipment that requires to be located between the central module and the wells. The pad 125 in the middle building block may, for example, have a guide which together with the guide pin 160 (fig. 17) enable the modules to be easily guided into position.

The building block units can be assembled to form a great number of different shapes, and extended both in the longitudinal and transverse directions. The solution provides a high degree of flexibility and enables the building blocks to be assembled in many different configurations for different combinations of subsea installations. The building blocks may be arranged beside one another or in a row.

In fig. 19 an example is illustrated of an assembly of a foundation building block 111 and a building block 113 (consisting of two pads 125 beside each other), giving a standard spacing between a single well with a well tree 5 and a production pipeline 6 via a T-spool 7. The same standard spacing is thereby obtained between well tree and T-spool as that between well tree and manifold illustrated in fig. 20. The foundation building block 111 is located above the production pipeline 6 so that the T-spool in the pipe remains located in the space between the pads 125. Alternatively, the foundation may be located on the seabed first and the pipeline lowered down to the foundation and locked thereto.

In fig. 20 the foundation in fig. 18 is illustrated extended with a cluster of four wells and well trees 5 operatively connected to a central manifold 2. The special advantage of the invention is clearly illustrated in this drawing, viz. that a process module can be tailor-made for a well so that an optimal treatment of the well fluids is achieved. As illustrated in the drawing a process module 40, which is a module for gas/liquid separation, is mounted between the well tree 5b and the manifold, while a booster module (pump module) 20 is mounted between the well tree 5c and the manifold. Fig. 21 shows a detail in fig. 20, giving a better illustration of how the connecting module is mounted. In the example the module is of the type illustrated in fig. 5, containing only a choke valve.

Fig. 22 shows the extended foundation in fig. 20, illustrating how the roof on each module and the top of the well trees form an integrated trawl protection 130 for the whole development.

In fig 23 a second example is illustrated of a device for locating wells relative to a centrally located manifold in such a manner that uniform spacing is obtained between well and manifold. A template 80 is first located on the seabed. This template will later form a support for a manifold. In the drawing an octagonal template is illustrated, thus permitting a development with eight wells. However, the template may have any number of sides according to the well requirement. A spacer 81 of the desired length is manufactured on land. The spacer is lowered to the seabed and fixed at one end to the template 80, its other end constituting a guide for guiding a bit for drilling a well 4. This is repeated for the number of wells that require to be drilled in the cluster. Each well will be equipped in the normal manner with a well tree 5 and finally a standard connecting module 10, 20 etc. is mounted between each well and the central manifold.

Alternatively, an adjustable and reusable spacer may be made, one end of which is hinged for releasable attachment to the template 80 and to the other end of which a standard type of guide basis is releasably attached. The spacer can thereby be released from the guide basis and template and moved to the next point where a well requires to be established. The invention has now been described by means of embodiments, but a number of variants and modifications of what has been described may be envisaged within the scope of the invention as defined in the following patent claims.

Claims

1. A well system for achieving flexible replaceability in the system, comprising at least one well (4) with a well tree (5) and a receiving station for well fluids produced by the well (4), characterised in that a well (4) and the receiving station are arranged at a distance apart corresponding to a multiple of a unit distance and that the connection between them is composed of at least one unit module with a length corresponding to a multiple of the unit distance, and at least one unit module is replaceable.

2. A well system according to claim 1, characterised in that the system further comprises angular unit modules.

3. A unit module for use in the well system according to claim 1, characterised in that the unit module comprises at least one fluid connector in at least two oppositely directed ends of the unit module, that the length between the fluid connectors corresponds to a multiple of the unit distance and further that the fluid connectors are adapted to be connected to fluid connectors on an adjacent unit module and/or to the well or the receiving station.

4. A unit module according to claim 3, characterised in that the unit module comprises process equipment between the fluid connectors at each end.

5. A unit module according to claim 3, characterised in that the unit module comprises an outer frame substantially corresponding to the outer limits of the unit.

6. A unit module according to claim 5, characterised in that at least one side of the outer frame comprises a protective cover.

7. A unit module according to claim 5, characterised in that the outer frame is substantially in the form of a box where a part of the box in cross section is designed with truncated corners forming inclined surfaces, and the fluid connectors are mounted at the inclined surfaces.

8. A method for formation of a well system, characterised in that a first location is established on the seabed, at least one second location, for example for a well, is established on the seabed in the desired direction and at a distance from the first location corresponding to a multiple of a unit distance for the system, a well is drilled and completed at a location and a receiving station is provided at a second location and at least one unit module is deployed between the receiving station and the well and connected thereto, where one or more unit modules are also replaced in the event of altered operating conditions.