The present invention relates to a communications system and, in particular, to a wireless data communications system for use within a hydrocarbon production system.

A hydrocarbon or oil well production system typically includes a complex network of metallic pipes which guide oil from an underground reservoir to a production platform. In the most complex production systems, the reservoir may be located within the ground beneath the sea meaning the production pipe system typically carries the oil from the seabed through a riser to a production platform on at the surface of the sea.

The production string is a part of an oil well that is composed of the production tubing and other completion components. When a well is first drilled, the outer casing is the first component run into the drilled well. Production tubing is then run into the drilled well after the casing is run in and cemented in place. The production tubing provides a continuous bore from the production zone to the wellhead through which oil and gas can flow from the reservoir to the surface. The production tubing not only contains the production fluids thus preventing them from contaminating the environment it also prevents production fluid from eroding the other well structures, such as the outer casing. Production tubing is typically between five and ten centimetres in diameter and is held co-axially inside the outer casing through the use of spacers.

If a well has more than one zone of production, multiple lines of production tubing can be run. Thus, in the most complex production systems "lateral" production tubing may branch off from the main riser to allow extraction from subsidiary reservoirs.

The term "production system" herein is used to refer to all the elements of the hydrocarbon extraction system including the outer casing tube and other components such as casing, sensors, controlled devices, valves, drill equipment, wellhead, and completion components. The production system may comprise multiple laterals and may penetrate up to 6 km below ground level. The oil reservoir may be within ground below the sea which may be up to 5 km deep. Command and control of production activities is typically carried out from the surface production platform. Valves and drilling mechanisms must be remotely controlled from the surface and these actions are often informed through analysis of sensor data from critical locations within the pipe structure.

Telemetry may recover data from sensors during the drilling operation and this data set is referred to as a "Measurements While Drilling" (MWD) system. Alternatively the system may operate in a Logging While Drilling (LWD) mode. To enable remote control operation as well as retrieval of such measured or logged data, there is a need for communication of data from remote sensors to the control centre and/or communication of command instructions from the control centre to control devices which may be remotely located; remote sensors and control devices also require electrical power and this must also be supplied from the control centre.

This requirement for remote data communication is extremely challenging due to the constraints of the production system. The existing pipe structure is the most accessible route for any data signalling mechanism and power supply. However, using the existing pipe structure, several mechanisms have been proposed for achieving this remote signalling capability.

"Mud pulsing" is a data transmission technique which uses variations in pressure in the mud fluid used as part of the production process as a coolant within the pipe system. Pressure variations are used to represent modulated data and thus are applied to the mud meaning the pressure variations are transmitted along the length of the pipeline. However, mud pulsing systems can suffer heavily from interference from the acoustic noise generated by drilling operations and therefore are only suitable for crude and low data transmission.

Acoustic signalling is another technique which has been developed wherein acoustic data signals are transmitted within the pipe walls and through the fluid carried by production pipes to be received at the other end of the production pipe. However, acoustic signalling in the environment of a hydrocarbon production system suffers from similar limitations as mud pulsing in that the acoustic noise generated by the drilling operations creates significant interference in the transmitted data signals. Hard wired conductive cable systems can provide data and power to remote locations within the pipe structure are unreliable in the extreme environment in that damage can occur easily but is it is highly problematic to carry out repairs.

For example, wireless connectors between a wired loom and equipment permanently attached to the production system allows replacement of the wire network for maintenance and modification. In some circumstances, a permanent hard wired loom will be connected to permanently installed instrumentation or equipment to be controlled. However, in each of these arrangements, failure in any part of the system in this extreme environment may disable the whole system. It may be impossible to repair in situ or to replace the system once deployed.

Furthermore, the production tubing and casing in which the called sections are deployed are assembled in sections and this complicates deployment of a wired system as underwater wet mating is required or close inductive coupling can be used. However each of these requires connective accuracy. The fluids which flow in the production tubing and casing contain abrasive materials, are often chemically reactive and at high temperature and pressure.

In addition, this environment electrically conductive cables and electrically conductive connectors provide very low reliability as damage can easily occur thus causing the entire communications system to be interrupted. Hard wired cables are permanently interfaced to control devices and sensors. If part of the system fails this often results in failure of the whole command and control network. This propensity for single point failure is highly undesirable.

In United States Patent 6360820 "Method and apparatus for communicating with downhole devices in a wellbore" Laborde et al. describes an inductive

communications system which requires close coupling between a first and second inductive coupler to allow data communications between devices deployed within a wellbore. However, it is commonplace for a range of equipment and tooling to typically be deployed within a wellbore so the requirement for close proximity between couplers is a significant practical limitation. This limitation also imposes the restriction of implementing only point to point communications. Since the couplers in this prior art can only communicate over very limited range within the confines of the wellbore it is not practical to bring several secondary couplers within communicating range of a first coupler to implement a wireless networking topology.

There is therefore a need for a flexible system for reliably providing data

communications to remote equipment within a sub-surface hydrocarbon production system.

According to a first aspect of the present invention, there is provided a

communications system for deployment within a subsurface hydrocarbon production system, the communications system comprising at least a section of production pipeline having an external pipe unit, and an internal pipe unit located within and coaxial with the exterior pipe unit creating a void therebetween operable to receive fluid, a first communication unit disposed at a first location on the internal pipe, operable to transmit an electromagnetic data signal, and a second communication unit located at a second location, remote to the first location, on the internal pipe, operable to receive an electromagnetic data signal transmitted by the first communication system through the fluid, internal pipe and external pipe.

By arranging a two communication units remote from one another upon an internal pipe, placed within an external pipe, with fluid flowing between the pipes, when the first unit transmits data using for reception by the second communication unit using electromagnetic signals, the internal and external pipe and fluid arrangement facilitates the transmission of the signal and therefore enables more effective data communication in this environment. The data may be compressed prior to transmission. Compression allows the occupied transmission bandwidth to be reduced. In this way, increased data rates can be transmitted over equivalent distances. Optionally, the data is compressed in combination with use of a lower carrier frequency. The lower carrier frequency leads to lower attenuation. This in turn allows data transfer through fluids over greater transmission distances.

Each communication unit may be provided with a transmitter or a receiver depending on whether the communication unit is to transmit or receive signals.

Preferably, the data transmission is bi-directional and each communication unit is provided with a transceiver. In this way, command and control signals can be transferred between the communications units enabling full communication between the bottom of the string and the platform.

Preferably, each transceiver has an electrically insulated magnetic coupled antenna. The antenna may be a wire loop, coil or similar arrangement. Such antenna create both magnetic and electromagnetic fields. The magnetic or magneto-inductive field is generally considered to comprise two components of different magnitude that, along with other factors, attenuate with distance (r), at rates proportional to 1 /r ² and 1 /r ³ respectively. Together they are often termed the near field components. The electromagnetic field has a still different magnitude and, along with other factors, attenuates with distance at a rate proportional to l/r. It is often termed the far field or propagating component. Such a transceiver is manufactured by the Applicant, WFS Technologies Ltd. There are two fundamental classes of electromagnetic antenna, electric field and magnetic field. Tubing employed in the construction of a hydrocarbon production system is typically steel with a high magnetic permeability and electrically conductive and it is in this environment the communications system is operable to provide wireless communications, namely within a confined space bounded by metallic tubing. Both the properties electrical conductivity and high magnetic permeability of the tubing influence the fields generated by electric or magnetic field antennas. Each antenna may be a magnetic field antenna and may be formed using multiple turns of wire arranged in a loop or around a solenoid.

Each antenna may further comprise a least one coil wound around the internal pipe.

Each antenna may alternatively be arranged on protrusion extending radially outwards from the internal pipe. Each antenna may alternatively be arranged on a protrusion extending radially inwards from the external pipe. The internal pipe may be formed of metal having a high magnetic permeability. The external pipe may be formed of metal having a high magnetic permeability. The arrangement of the coil upon the internal pipe or in the void between the internal and external pipes, which have high magnetic permeability, facilitates magnetic coupling of the signal to at least one of the internal and external pipe and thus enhances the magnetic flux density of the transmitted data signals thus facilitating transmission over workable distances within the production pipeline structure.

Each antenna may be an electric dipole antennas are used to implement the transducers for the communications transceivers. Each electric dipole antenna may be typically realised using two aligned quarter wavelength lengths of wire fed with a balanced drive at their joining point wherein a length of electrically conductive wire is positioned within the annular space between production tubing and casing.

The external pipe may be outer casing. The internal pipe may be production tubing. At least one centralising collar may be arranged between the external pipe and internal pipe to ensure the internal pipe is retained concentrically with and co-axially relative to the external pipe. A communications unit may be located within a centralising collar. Centraliser collars each provided with a communications unit are positioned at regular intervals along the production string pipeline for mechanical reasons so this dual functionality benefits installation efficiency and provision of such a string of communications unit enables wireless communication over a large extent of the pipeline. The centraliser collar may be adapted to electrically connect the internal pipe to the external pipe at predetermined locations. The centralised collar may act as a communications unit antenna by providing a modulated alternating voltage between the internal pipe to the external pipe. Such an arrangement generates a large long loop current which in turn generates an alternating magnetic signal which can be used as a means of remote signalling. A communications unit may be provided at a wired loom and similarly another communications unit may be provided at equipment permanently attached to the pipe line. Such an arrangement can allow replacement of wired network components whilst still enabling communication between other components or sensors and the control unit. Therefore, failure of individual sensor or valve communications nodes will not affect the ability of data to be communicated from other components in the system provided with communications units.

The communications system may be implemented to optimise smart well production through using real time sensor data to determine optimum valve positions in laterals at any given time.

In another embodiment of the present invention there is provided a downhole electrical valve actuation system using wireless data connectors to enable

connectors to be mated and unmated remotely.

The communications system may further comprise a large diameter loop antenna deployed on the mud line. The magnetic field generated by a loop antenna increases with the area enclosed by the loop and in this application a loop greater than 3 m diameter is considered to be large.

The mud line, or seabed loop, may act as an antenna for a relay transceiver operable to communicate with at least two remote communication units. The seabed transceiver communicates through the seabed to multiple nodes distributed throughout the production system.

The mudline loop antenna may act as a transducer for the relay transceiver enabling cabled communications, electromagnetic signalling or acoustic transmission through water between the relay transceiver and the control unit.

A chain of repeaters may be required to facilitate through water electromagnetic signalling to relay the data from the control unit to the relay transceiver deployed at the seabed.

The communications units may be provided a battery power source. The

communications units may be provided with a power generation facility. The power generation facility may generate power generated by means of a dynamo system which derives power from the flow of fluid through the void which acts to drive a rotational impeller. The power generation facility may use vibration as an energy source to locally derive electrical power.

The external pipe may be discontinuous. The external pipe may be from with inlet and/or egress pipes extend out from the external pipe wall. Such discontinuities or inlets or outlets form gaps in the external pipe which enables the input or output of material into the void. Such discontinuities do not impinge significantly upon the data transfer ability of the communication system as although a slight dip in the signal is observed during transmission across the gap formed by the discontinuity, the transmission of the signal is continuous again after the gap.

According to a second aspect of the invention there is provided a communications system comprising a pipeline having an elongate outer tube within which is co-axially located an elongate internal member with a void created between the pipeline and the internal member, the void operable to receive fluid; a plurality of communications units located along the internal member, each operable to transmit and/or receive a data carrying signal, at least one communication unit being in communication with the control unit and at least one sensor in communication with at least one communication unit, wherein the at least one sensor is operable to provide sensor data to at least one communication unit which then transmits the sensor data to at least one other communication unit.

The pipeline may be provided with a first end and a second end. A control unit may be located at the first end of the pipeline. The sensors may be located at the second end of the pipeline. Multiple sensors may be located along the extent of the pipeline. The sensor data may be transmitted from the communication unit via any

intermediate communication units to the control unit.

Preferably, the data is transmitted as an electromagnetic and/or magneto-inductive signal. Signals based on electrical and electromagnetic fields are attenuated in fluids depending upon their electrically conductive nature, for example, signals in water based fluids are attenuated rapidly due to the partially electrically conductive nature of water. Propagating radio or electromagnetic waves are a result of an interaction between the electric and magnetic fields and the high conductivity of seawater attenuates the electric field. However, water based fluids often have a magnetic permeability close to that of free space so that a purely magnetic field is relatively unaffected by this medium. For propagating electromagnetic waves the energy is continually cycling between magnetic and electric field and this results in attenuation of propagating waves due to conduction losses. Fluids typically provide attenuation losses in a workable bandwidth which provides for data transmission over practical distances of up to 10 metres.

The data may be compressed prior to transmission. Compression allows the occupied transmission bandwidth to be reduced. In this way, increased data rates can be transmitted over equivalent distances. Optionally, the data is compressed in combination with use of a lower carrier frequency. The lower carrier frequency leads to lower attenuation. This in turn allows data transfer through fluids over greater transmission distances. Each communication unit may be provided with a transmitter or a receiver depending on whether the communication unit is to transmit or receive signals. Preferably, the data transmission is bi-directional and each communication unit is provided with a transceiver. In this way, command and control signals can be transferred between the communications units enabling full communication between the at least one sensor and the control unit. Temperature, pressure, flow rate are common parameters measured by the at least one sensor which act as a data source or data sources within the presently described system.

The elongate outer tube may be outer casing. The internal member may be production tubing. The elongate outer tube may be discontinuous. The elongate outer tube may be formed with inlet and/or egress pipes extending out from the elongate outer tube wall. Such discontinuities or inlets or outlets form gaps in the outer tube which enables the input or output of material into the void. Such discontinuities do not impinge significantly upon the data transfer ability of the communication system as although a slight dip in the signal is observed during transmission across the gap formed by the discontinuity, the transmission of the signal is continuous again after the gap.

The communications system may be deployed within a subsurface hydrocarbon production system.

At least one centralising collar may be arranged between the elongate outer tube and elongate internal member to ensure the internal member is retained co-axially relative to the elongate outer tube. A communications unit may be located within a centralising collar.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a schematic illustration of a hydrocarbon production system incorporating a communications system according to an aspect of the present invention; Figure 2 is a block diagram of a communication unit for use in the communications system of Figure 1 ;

Figure 3 is a schematic diagram of an antenna unit for use in the communication unit of Figure 2;

Figure 4 is a schematic diagram of a communications system according to an aspect of the invention;

Figure 5 are schematic diagrams of a section of communications unit according an aspect of the invention;

Figure 6 is a schematic diagram of a section of communications unit according to an aspect of the invention; Figure 7 is a schematic diagram of a section of communications unit according to an aspect of the invention;

Figure 8 is a schematic diagram of a section of communications unit according to an aspect of the invention;

Figure 9 is a schematic diagram of a section of a communications system according to an aspect of the invention;

Figure 10 is a schematic diagram of a communications system according an aspect of the invention, and Figure 1 1 is a schematic diagram of a communications system according to an aspect of the present invention.

Reference is initially made to Figure 1 of the drawings which schematically illustrates a hydrocarbon production system generally indicated by reference numeral 2 which incorporates a communications system 4 according to an embodiment of the invention.

The production system 2 comprises a riser 13 which links lower stack 16 at the seabed 10 with topside rig 1 1 . A control centre 19 for the hydrocarbon production system is, in this case, located within the topside rig, or platform 1 1 . Wellhead 12 penetrates into seabed 10 providing access to primary well 14a which has lateral branches 14b and 14c which form the subterranean production system 8. Downhole sensors 17b and 1 7c are located in laterals 14b and 14c respectively, and downhole tool 15 is located in lateral 14a, each are remote from the control centre 19.

Communications system 4 comprises a plurality of communications units, in this case transceivers 1 8a- 1 8g, which are disposed around the hydrocarbon production system and provide wireless communications between the deployed equipment 1 5, 1 7b and 17c within the production string and the control centre 19. Control centre 19 is provided with a transceiver 18a, transceiver 18b is located in riser 1 3; transceivers 1 8c, 18e and 18f are located in primary bore 14a with transceiver 18c located at the branch junction between primary bore 14a and lateral 14b and transceiver 18e located at the branch junction between primary bore 14a and lateral 14c, transceiver 1 8d is located in lateral 14b and transceiver 18g is located in lateral 14c.

Reference is now made to Figure 2 of the drawings which illustrate parts of the transceiver 21 of communication unit or coupling node 18. In transceivers 21 the sensor interface 49 receives data from the deployed sensor units 1 7c, 17b which is forwarded to data processor 48. Data is then passed to signal processor 43 which generates a modulated signal which is modulated onto a carrier signal by modulator 42. Transmit amplifier 41 then generates the desired signal amplitude required by transmit transducer 40. In the transceiver 21 , there is a control interface 150 which sends command signals to the data processor 48 which are transmitted by the above described path.

The transceivers 21 also have a receive transducer 47 which receives a modulated signal which is amplified by receive amplifier 46. De-modulator 45 mixes the received signal to base band and detects symbol transitions. The signal is then passed to signal processor 44 which processes the received signal to extract data. Data is then passed to processor 48 which in turn forwards the data to control interface 150. The transceivers 21 may be provided with a memory for data storage (not shown). In use, downhole sensors 17b and 17c monitor parameters of interests which may include parameters such as pressure, temperature, valve position, flow rate or other relevant data and generate data which is passed to sensor interface 49 and then onto data processor 48 where it is processed to generate a form which can be interfaced with transmit transducer 40.

Similarly when receive transducer 47 receives a modulated signal from another communications unit 18, it process the signal to generate a data stream which is forwarded to data processor 48. If the communications unit is transceiver 18a, associated with the control unit 1 9, this data is then presented at control interface 50 which acts to enable control of equipment deployed within the production system. If the communications unit is an intermediate transceiver, say 18c, then the data is presented at control interface 50 before being sent on through signal processor 43 to transmit transducer 40 for onward transmission. Figure 3 of the drawings illustrates an antenna arrangement which is indicative of the arrangement suitable for use in transceiver 21 as the antenna for transmit transducer 40 and/or receive transducer 47. In this case, the antenna comprises a high permeability ferrite core 80. Wound round the core 80 are multiple loops 82 of an insulated wire. The number of turns of the wire and length to diameter ratio of the core 80 can be selected depending on the application. However, for operation at 1 25kHz, one thousand turns and a 10:1 length to diameter ratio is suitable. The antenna is connected to the relevant transmitter/receiver assembly parts described in Figure 2.

With reference to Figure 4 of the drawings, which illustrates a schematic cross section detail of a section of a well bore, or lateral, 14 wherein is located a production tubing 51 which is typically constructed from a steel alloy is positioned co-axially concentric to casing 50. The void 52 formed between the outer surface of production tubing 51 and the inner surface of casing 50 may also be referred to as annular space 52 and it is within this annular space that mud, or fluid, 53 flows and in which the communications system components are deployed. In this embodiment coil antenna 82a is the antenna for a transceiver (not shown) which is part of

communications unit 18a. The loops 82a are wrapped around the outer surface at a first end 54 of the production tubing 51 , which acts as a high permeability core. Coil antenna 82b, which is the antenna for a transceiver which is part of communications unit 18 is wrapped around the outer surface at a second end 55 of production tubing 51 . This type of coil transducer arrangement may be incorporated in a collar or centralising collar (not shown).

In use, when a signal is transmitted by antenna 82a, production tubing 51 acts to couple magnetic flux generated and a field pattern 56 is set up as the production tubing has high magnetic permeability and this property will act to enhance the magnetic flux density intersecting antenna 82b so that a useful signal strength is received by communications unit 18b. Thus the arrangement of communications units 18a and 1 8f and production tubing 51 operate as a coupling device. The annular space 52 between production tubing 51 and casing 50 acts as a waveguide for electromagnetic waves output from communications units 18 thus the electromagnetic waves can propagate along a length of the production tubing 51 and casing 50. Waveguides which occur in such enclosed areas have a minimum frequency at which propagating waves can be supported and this is related to the wavelength of the signal compared to the width of the enclosed space, this is a known problem associated with electromagnetic communications within a metallic pipe structure and is known as the waveguide cut-off frequency. This can be overcome by use of a higher carrier frequency, for example a carrier frequency of above 1 0 MHz may be used to allow propagating signals within the pipe structure above the cut-off frequency. In Figure 5 there is shown a schematic cross section detail of another embodiment of a communications system components located within a section of well bore 14 which enables communication within a pipe, in this case casing 50. Communications units 1 8c and 18e are located in void 52. In this embodiment, each communications unit transceiver has a separate receive antenna 93 and transmit antenna 95. Each receive antenna 93c, e comprises three solenoid or loop antenna 94a, 94b, 94c which are arranged with their axes mutually perpendicular to one another to allow spatial diversity. In this embodiment a single transmit antenna 95c, e within each

communications unit 18c,e respectively is used to generate a magnetic flux field while for reception, antenna 93c, c uses the multiple receive antenna 94a, b, c to provide angular diversity to allow efficient reception of magnetic flux independent of orientation or distortion of the magnetic field by local metallic components.

Figure 6 shows a schematic cross section of a portion of a communications system in accordance with another embodiment of the invention. In this embodiment a coupling device, or communications unit 1 8, is installed on the surface of production tubing 51 such that it protrudes in the void 52 between production tubing 51 and casing 50. The communications unit 18 comprises a flux splitter 1 12 bonded onto pipe 51 where the flux splitter 1 18 is, in this example, formed for a high magnetic permeability material which preferentially has higher permeability than the material of the pipe 51 . Coil antenna 82 is wound around flux splitter 1 1 2 with transceiver 21 located in void 1 14 formed between the flux splitter 1 1 2 and pipe wall 51 .

In use, magnetic flux launched by a first communications unit (not shown) within a ferrous pipe such as tube 51 will be guided by the pipe walls and concentrated within the pipe walls by the material's high permeability. Some of the magnetic flux flowing through the pipe 51 will be diverted through the flux splitter 1 12 which can then be enclosed by coupling coils 81 to induce a signal. By effectively enclosing the magnetic flux, the signal is induced in coils 81 more effectively than would be possible for a transceiver merely located upon a pipe. It will be appreciated that the flux splitter may be a component of a collar or centralising collar (not shown). The coupling device flux splitting system of communications unit 18 could also be used to launch flux, in effect to launch a signal, into the pipe 51 and in this arrangement coupling coils 81 carry current which generates flux in the pipe wall thus acting as a transmit transducer in a communications unit. Figure 7 shows a schematic cross section of a portion of a communications system in accordance with another embodiment of the present invention. In this embodiment, a centralising collar 70 which is provided with an outer rim 71 a and inner rim 71 b between which four struts 72a, b, c and d extend radially. Each strut 72a,b,c,d has wound around it a coil 82a,b,c,d respectively each of which is in effect a solenoid. These coils 82a,b,c,d act as antenna for transceiver 21 (not shown) of a

communications unit 18 (not shown) within the communications system such as that shown in Figure 1 . It will be appreciated that whilst this embodiment illustrates an arrangement with four struts and thus antenna, the collar may be provided with any number of struts, typically arranged spaced evenly apart, each of which may be wound with a coil antenna.

Figure 8 shows a schematic illustration of a section of a communication unit according to an aspect of the present invention. In this embodiment, the

communication unit 18 comprises a core 80 which is secured to the exterior of pipe 51 and around which is wound a plurality of coils 82. This antenna arrangement enables the transmission and/or reception of an electromagnetic signal along the pipe 51 . Such a communications unit may be used in any of the systems detailed herein. Figure 9 shows a schematic illustration of a section of a hydrocarbon production system pipeline 14 comprising a pipe 14f and a pipe 14g which are separated by a disconnect 1 1 2 which may be mud or may be some other fluid or solid such as seawater, oil, sand or the like. The pipe 14f is provided at the distal end with a communications unit 18m. The pipe 14g is provided with a communications unit 1 8n at the distal end closest to pipe 14f; a communications unit 18o and communications unit 18p which is located adjacent sensor unit 17m. In use, the communications unit 1 8p can receive sensor data from sensor 17m and then using transmission along the pipe 14g, provide said data to 18o which in turn provides said data to

communications unit 18n. Communications unit 18n is then operable to transmit the sensor data across the disconnect 1 1 2 to communications unit 18m from where subsequent communications units (not shown) can continue to transmit the data such that it is provided to a control unit (not shown). Such an arrangement enables transmission of data, using the communications system, across a disconnect in the pipeline 14.

Figure 10 shows a schematic illustration of a hydrocarbon production system similar to that of Figure 1 , with like parts similarly enumerated, the system generally indicated by reference numeral 2 which incorporates a communications system 4 according to an embodiment of the invention. In this embodiment, the

communications system 4 is provided with communications units 18a - g as in Figure 1 . However, an additional communications unit 18h is provided at the mudline 10 which is provided with an antenna 82h which is a large diameter loop antenna located on the seabed 10. As the magnetic field generated by a loop antenna increases with the area enclosed by the loop, in this embodiment the loop antenna 82h would have a diameter of greater than 3m. Antenna 82h will enable the relay transceiver, or communications unit 1 8h, to communicate with at least two remote communication units 18a, 18b and 18c, 18e. The seabed communication unit 1 8h communicates through the seabed to communications units 1 8c - g which are distributed throughout the subsurface production system.

A chain of repeaters, such as communications units 18a and 1 8b can to facilitate communication from the platform 1 1 through riser 13. However, alternatively a chain of repeaters (not shown) using through water electromagnetic signalling to relay the data from the control unit to the relay transceiver deployed at the seabed may be used, or alternatively cabled communications may be used (not shown).

In Figure 1 1 there is shown a cross section of a section of a schematic cross section detail of a section of a well bore, or lateral, 14 wherein is located a drill pipe 51 which is typically constructed from a steel allow positioned co-axially concentric to casing 50. The cladding pipe, or casing, 50 is discontinuous in that a gap 56 is formed between an end face 54a of a first end 54 of casing pipe 50 and end face 55a of a second end 55 of casing pipe 50. The void 52 formed between the outer surface of production tubing, or drill pipe, 51 and the inner surface of casing 50 may also be referred to as an annular space 52 and it is within this annular space that mud, or fluid, 53 flows and in which the communications system components are deployed. In this embodiment, transceiver 21 a which is part of communications unit 18 (not shown) is secured against the outer surface of drill pipe 51 . Another transceiver 21 b which is part of another communications unit (not shown) is secured at the outer surface of the drill pipe 51 at the second end 55. In this arrangement, the inner pipe 51 carries the flux transmitted by transceiver 21 a. As the inner pipe 51 is continuous, the flux is carried continuously in a consistent manner. However, the flux must bridge gap 56 at outer wall 52 to return and therefore the gap 56 causes a temporary fall in flux density in the transmitted flux with a corresponding expansion in transit area for the returning flux occurring at gap 56. With the flux running longitudinally in the pipe walls, the eddy current is emitted radially. However, as the flux bridges the gap 56, transmission of data from communications unit 21 a to communications unit 21 b is achieved successfully. Thus, when a lateral includes a discontinuity in the outer wall 50, transmission of data along the pipeline can still be achieved effectively thus enabling communication to occur over a useful bandwidth.

It will be appreciated that in the above detailed embodiments, multiple repeaters, or communications system can be deployed along a string spaced so that each repeater is positioned close to a lateral where it can wirelessly communicate with sensors and actuators within each lateral pipe.

The communications unit 18a located closest to the platform can be linked to the control centre by means of hard wired cable. This cable may provide data communications over a fibre optic link or power and/or data over an electrically conductive cable. Indeed, whilst electromagnetic fields and/or magneto-inductive signals are detailed as being used as a signalling mechanism to remote equipment such as sensors 17 and tool 15, it will be appreciated that part of the communication distance between the control centre and such remote equipment could also be covered through conductive cabling. The presently described system can simply be implemented to facilitate wireless coupling of data at least over the final interface between a transceiver in cabled communications with the control centre and a remote device deployed within the production string.

Downhole fluids are typically found to be at high temperature and pressure. The coupling nodes of the present invention will typically be required to operate within a fluid at elevated temperature and pressure compared to many more conventional electronics applications. Cooling of power transfer circuits will present a

considerable challenge. Peltier thermoelectric local cooling may be required to maintain efficient operation of key circuit components. The oil and gas industry refers to these requirements as High Pressure High Temperature (HPHT) reservoir conditions. Signalling mechanisms using the communications systems described herein use electromagnetic or magneto-inductive signals which can support medium range wireless communications throughout the well bore thus, communicating transceiver devices are not required to be positioned in close proximity to achieve

communications. Because of the wireless communicating range of the transceivers, several communication units, or couplers, may be positioned within communicating range of each other within the confines of the wellbore. This capability enables the implementation of wireless networking configurations. In the above embodiments, data modulated onto a carrier signal may be encoded to carry an address which corresponds to the communication unit, or coupling node which is intended to receive a specific data packet thus ensuring that data is transmitted to the appropriate end point. In this way, in complex well systems having a number of branches or pipelines, intermediate nodes may relay data intended for a third coupling node which is beyond communicating range with the first node. This communication system has enhanced deployment flexibility compared with an alternative based around coupling nodes which can only communicate point to point. Furthermore, the network can be enhanced or repaired by the addition of new nodes or replacement of individual or multiple communicating nodes. An alternative system based on single point to point couplers would rely on the supporting cabled network to implement node addressing and so require cable loom modification for

replacement or addition of communicating nodes.

The present invention provides reliable real-time data from any location within the production system; improving reservoir management, well bore planning and resource exploitation. Wireless transfer of communications data and/or power to remote locations within the production system provides a flexible command and control function which can be implemented effective and in real time from the remote control unit which is typically located in an above surface platform facility.

It will be appreciated that the communications system described in the above embodiments may be installed and utilised during any phase of the life of the well bore, including drilling, logging, testing, completing, producing, maintenance, workover and decommissioning. The communications system may implement command, control and instrumentation function depending on the particular requirement of the system deployed. In addition, the system may provide bidirectional communications or single directional communications where required. Similarly, it will be appreciated that the wireless communications system described in this application could alternatively be applied to a Floating Production, Storage, and Offloading (FPSO) based system or a land based subsurface production system. Whilst a loop antenna wound around the internal pipe has been detailed above, it will be appreciated that each magnetic field antenna may be designed to have a long thin form in order to be compatible with the dimensional requirements imposed by deployment within a production string. A large enclosed loop area may be achieved by running the loop along the length of a pipe section with a width bounded by the width of the pipe internal diameter.

While magnetic flux generated by a loop or solenoid antenna is proportional to its enclosed area, the dimensions of typical oil production tubing will practically limit the size of the antennas shown herein. However, the signal coupling between two coils improves as frequency increases so carrier frequency can be increased to mitigate this limitation In terms of antenna area size. In some environments, a carrier frequency of above 100kHz will prove beneficial.

The descriptions of the specific embodiments herein are made by way of example only and not for the purposes of limitation. It will be obvious to a person skilled in the art that in order to achieve some or most of the advantages of the present invention, practical implementations may not necessarily be exactly as exemplified and can include variations within the scope of the present invention. For example, whilst the communication system is described herein in relation to data communications within a hydrocarbon production system the communications system could similarly be used in any industrial pipe based system where there is a requirement for data

communications transfer from remote equipment. In a further alternative, as the pipe walls within a production system are typically constructed from steel alloy which is electrically conductive. Direct conductive signalling may alternatively be used as a signalling mechanism for the transducers of the present system. A potential difference can be generated between a production tube and outer casing and this can be sensed at a remote receiving transducer as a means of signalling.

Centralising collars may be adapted to launch and recover these electrical signals.