GB2361597A - Underwater optical fibre communication system - Google Patents

Abstract

Communications apparatus is disclosed which is arranged to provide communication between a plurality of locations, one of which comprises a platform (4, 6) and the others of which comprise wells (1-3). The apparatus comprises a plurality of optical communication units (9-11) associated with respective locations, each unit comprising an optical transmitter (13-16) and an optical receiver (17-20) connected in duplex operation, the apparatus further comprising at least one optical amplifier (32, 33, 34) and an optical fibre arrangement (25) in communication with the units, the fibre arrangement including a common optical fibre (25) for the units. Where the platform (4, 6) and wells (1-3) comprise a hydrocarbon extraction system, preferably in an underwater environment.

Description

2361597 COMMUNICATIONS APPARATUS This invention relates to apparatus for

providing communication between wells and a platform in a hydrocarbon extraction system.

Use of the term "platform" is intended to include all types of hydrocarbon collection facilities, such as offshore oil and gas installations, ships and other sea vessels, as well as land based oil and gas installations. Likewise, use of the term "wells" is intended to include both subsea and subterranean oil and gas wells.

Taking, as an example, communications between a vessel on the sea surface and subsea wells, data is transmitted between optical conimunications apparatus on the vessel and similar apparatus associated with each well via optical fibres included in an umbilical. An optical fibre is provided for each well, to permit independent communication between the respective wells and the vessel. However, as the umbilical also provides all other essential services between the vessel and the wells, the inclusion of optical fibres for communication increases the cost and complexity of the umbilical.

The invention provides communications apparatus arranged to provide communication between a plurality of locations, one of which comprises a platforin and the others of which comprise wells, the apparatus comprising a plurality of optical communication units associated with respective locations, each unit comprising an optical transmitter and an optical receiver connected in duplex operation, the apparatus ftirther comprising at least one optical amplifier and an optical fibre arrangement in communication with 2 the units, the fibre arrangement including a common optical fibre for the units.

The inclusion of an optical amplifier permits the communications system to work in conjunction with a single common optical fibre; the amplifier compensates for losses which would be encountered with providing communications to a number of separate locations via a common fibre. Thus, the umbilical need only accornmodate one optical fibre.

Use of the term "optical transmitter" is intended to include any type of optoelectronic device capable of generating an optical signal representing an electrical signal.

Likewise, use of the term "optical receiver" is intended to any type of optoelectronic device capable of generating an electrical signal representing a light signal. Use of the term "optical" is intended to include radiation at the infra-red and ultra violet ends of the spectrum, as well as visible light.

The invention allows multiplex communications between a platform and wells to be carried out. The multiplexing may be either in the frequency domain or in the time domain, or in a combination of both.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure I is a schematic drawing of a subsea well system; Figure 2 is a schematic diagram of a communications system constructed according to a 3 first embodiment of the invention; Figure 3 is a schematic diagram of a communications system constructed according to a second embodiment of the invention; Figure 4 is a schematic diagram of a communications system constructed according to a third embodiment of the invention; and Figure 5 is a schematic diagram of a communications system constructed according to a fourth embodiment of the invention.

Figure 1 illustrates a subsea well system, comprising a plurality of wells, the heads 1, 2, 3 of which are shown in this drawing. A sea vessel 4 is in communication with the well heads I to 3 by means of a so-called umbilical 5. The umbilical carries a variety of feeds, including electrical power and signals, hydraulic power and fibre optic cables, and is thus an expensive and bulky item. The umbilical terminates at a subsea manifold system 6, located on or near the seabed in proximity to the well heads 1 to 3. A multiservice connector 7 provides the interface between the umbilical 5 and the subsea manifold 6. The multi-service connector 7 is a both complex and expensive item as it has to operate reliably at considerable sea depths.

Equipment on the vessel 4 needs to communicate with equipment located in the wells, and vice versa, and to this end a communication system is provided, such as that illustrated in Figure 2.

4 In this drawing, the box indicated generally by the reference numeral 8 is intended to represent equipment located on the vessel 4. Similar equipment is shown in boxes 9, 10 and 11 in this drawing, and these are intended to represent equipment associated with the well heads I to 3 respectively. Some equipment is included in the manifold system 5 6, and this equipment is shown in the box indicated generally by the reference numeral 12.

Each of the boxes 8 to 11 includes an optical communications unit comprising an optical transmitter 13-16, arranged to produce a modulated light signal representative of an electrical quantity, and an optical receiver 17-20 arranged to detect optical signals and generate corresponding electrical signals. The transmitter and receiver of each of the units 8 to 11 is connected via respective duplexers 21-24. Each duplexer 21-24 ensures that light emerging from the transmitter is directed into an optical fibre emerging from the unit, and not back into the receiver. Similarly, the duplexer also ensures that incoming light signals are directed to the receiver only. In practice, however, it has been found that there is usually leakage of light into the unwanted direction.

In accordance with the invention, communication is made between the optical communications units 9 to 11 associated with the wells and the unit 8 associated with the platform by means of a fibre optic arrangement which includes a common optical fibre 25. The common fibre extends from the unit 8 on the platform to the subsea manifold 6. Inside the manifold 6, the common fibre 25 encounters a series of optical splitters 26 to 28. Taking the case of a time multiplexed system, the splitters arc arranged to direct a portion of light transmitted through the fibre into optical fibres 29, 3 0, 3 1 associated with the units 9, 10 and I I respectively.

In the case that communication between the units is time-multiplexed, partially silvered mirrors may be employed as splitters. In the case of frequency-multiplexed communication, Bragg gratings may instead be used.

Light emerging from the transmitter 13 in the platform travels along the common fibre 25, until it encounters the splitter 26 in the manifold. A predetermined portion of light is re-directed towards communications unit 9, via the optical fibre 29. The remainder of the transmitted light passes along the next section of fibre 25' until it encounters the splitter 27. At this point, another predetermined portion of light is redirected to communications unit 10, via fibre 30. Again, the remainder of the transmitted light travels down the next section of fibre 25", until splitter 28 reflects a predetermined portion to unit I I via fibre 3 1, and so on.

The use of splitters means that each of the units 9 to 11 only receives a portion of the light transmitted from the optical transmitter 13 located in the unit 8. Normally, this reduction in optical power would be prohibitive. However, optical amplifiers 32, 33 and 34 are provided in order to amplify the light signal immediately before it is received by the respective optical receiver 14, 15, 16. The insertion of an optical amplifier effectively increases the sensitivity of each receiver.

Ideally, the splitters are chosen so that substantially the same proportion of the initially 6 transmitted light is directed to each receiver. However, in practice, identical splitters are likely to be used for cost reasons, with the result that the receivers receive different light levels. In the case of a frequency-multiplexed system, the light is split according to frequency, so that almost all of the light at a particular frequency can be directed to 5 the appropriate receiver.

Information relating to the wells is relayed to the transmitters 18, 19 and 20 for communication in different time periods, or at different frequencies, to the platform. Optical signals transmitted by transmitter 18 emerge from the duplexer 22 and travel along fibre 29. The signals are then directed into the common fibre 25 by means of the splitter 26, for transmission to the receiver 17 located in the unit 8. Likewise, light signals from transmitter 19 emerge from the duplexer 23 and travel through fibre 30 and splitter 27. Here they are redirected into fibre 25', for transmission to the unit 8 via the splitter 26 and common fibre 25. In a similar fashion, light signals from transmitter 20 are directed to the receiver 17 by means of the duplexer 24, fibre 31, splitter 28, fibre 25", splitter 27, fibre 25', splitter 26 and common fibre 25.

With respect to light signals transmitted from the units 9, 10 and 11 back to the platform unit 8, it will be appreciated that a certain proportion of the light signals will be lost through the splitters and duplexers. Accordingly, an optical amplifier is also provided in the unit 8, in order to amplify the incoming light signal immediately before it is received by the optical receiver 17.

An alternative arrangement of the invention is shown in Figure 3). In this embodiment, 7 the optical amplifiers 32, 33 and 34 have been omitted, but instead there is a second optical amplifier 36 located in the unit 8. The optical amplifier is inserted in the path of the optical transmitter 13, and serves to amplify the outgoing light signal from the platform, in order to compensate for losses caused by the splitters 26, 27, 28 and the duplexers 22, 23, 24. The advantage of this configuration is that there is generally more electrical power available at the platform end of the system than at the well heads or down hole.

A further alternative embodiment of the invention is illustrated in Figure 4. In this embodiment, the fibre optic arrangement is arranged in a tree-like configuration. Light is transmitted from the unit 8 into the common optical fibre 25. At the first splitter 37, which is encountered in the manifold, the light signal is split into two equal portions.

The light signals emerging from the two branches of the splitter are, in turn, input to two subsequent splitters 38, 39 via respective optical fibres 40, 41. These splitters also split the light into two equal portions which find their way into the optical units 9, 10, 11 (and a further unit 42 is shown in this drawing) by means of optical fibres 43, 44, 45, 46.

The light signals are then directed by the duplexers 22, 23, 24, 47 into optical amplifiers 32, 33, 34 and 48 respectively for reception by the receivers 14, 15, 16, 49.

Taking the reverse direction, light signals from transmitter 18 emerge from the duplexer 22 and are transmitted along optical fibre 43 to splitter 38. The splitter 38 then sends the light signals along fibre 40 to splitter 37 which, in turn sends the signals to the unit 8 8 through the common fibre 25. From here, the signals are sent, via duplexer 21, to the amplifier 35 and hence to the receiver 17.

Similarly, light emerging from transmitter 19 travels to the receiver 17 by way of duplexer 23, fibre 44, splitter 38, fibre 40, splitter 37, common fibre 25, duplexer 21 and amplifier 35. Similar routes can be traced for each of the other transmitters. It should be noted that, for at least part of their journey, all light signals travel along the optical fibre 25.

Figure 5 illustrates an alternative arrangement of the apparatus of Figure 4, in which the optical amplifiers 32, 33, 34, 48 associated with the units 9, 10, 11 and 42 are omitted.

Instead, a second optical amplifier 36 is included in the unit 8 on the platform, just as in the Figure 3 embodiment of the invention.

As a practical point, account must be taken of the saturation limits of the optical fibre, the splitters and the duplexers when designing a communication system of this type.

Although the invention has been described with respect to wholly time-multiplexed or frequency-multiplexed communications, it will be appreciated that the invention permits both types of multiplexing to be employed.

The invention enables data communication to be carried out via a single fibre optic cable in the umbilical, thus reducing the complexity of the umbilical and the connector to the subsea manifold, The result is a substantial reduction in the cost of the umbilical 9 and the connector, as we'll as reduced testing time.

Claims (16)

1. Communications apparatus arranged to provide communication between a plurality of locations, one of which comprises a platform and the others of which comprise wells, the apparatus comprising a plurality of optical communication units associated with respective locations, each unit comprising an optical transmitter and an optical receiver connected in duplex operation, the apparatus further comprising at least one optical amplifier and an optical fibre arrangement in communication with the units, the fibre arrangement including a common optical fibre for the units.

2. Apparatus as claimed in claim 1, wherein the optical amplifier is incorporated in the optical communication unit associated with the platform.

3. Apparatus as claimed in claim 2, in which the amplifier is arranged to amplify light signals from the transmitter of the unit associated with the platfonri.

4. Apparatus as claimed in claim 2, in which the amplifier is arranged to amplify light signals for reception by the receiver of the unit associated with the platforin.

5. Apparatus as claimed in any one of claims 2 to 4, further comprising a second optical amplifier incorporated in the communication unit associated with the platform, the amplifiers being arranged so that one of them is arranged to amplify light signals from the transmitter and the other of them is arranged to amplify light signals for reception by the receiver.

6. Apparatus as claimed in any preceding claim, wherein at least one of communication units associated with the wells includes an optical amplifier.

7. Apparatus as claimed in claim 6, wherein the or each amplifier is arranged to amplify light signals from the respective transmitter.

8. Apparatus as claimed in claim 6, wherein the or each amplifier is arranged to amplify light signals for reception by the respective receiver.

9. Apparatus as claimed in any preceding claim, wherein the common optical fibre is arranged to extend between the communication unit associated with the platform and a manifold.

10. Apparatus as claimed in claim 9, wherein the optical fibre arrangement includes optical fibres extending between the communication units associated with the wells and the manifold.

11. Apparatus as claimed in claim 10, wherein the manifold includes an optical splitting arrangement arranged so that, in use, light signals transmitted from the platform communication unit through the common optical fibre are directed into the respective optical fibres communicating with the units associated with the wells.

12. Apparatus as claimed in claim 11, wherein the optical splitting arTangement is arranged so that, in use, light signals transmitted from the units associated with the wells 12 through the respective optical fibres are directed into the common optical fibre.

13. Apparatus as claimed in claim 11 or 12, wherein the splitters include Bragg gratings.

14. Apparatus as claimed in claim 11, 12 or 13, in which the splitters include partially silvered mirrors.

15. Apparatus, substantially as herein before described, with respect to, or as illustrated in, the accompanying drawings.

16. A hydrocarbon extraction system including a communications apparatus as claimed in any preceding claim.