Telecommunications technology offers the offshore industry many alternatives to link up offshore and onshore locations to effectively coordinate offshore related activities. EPMI's offshore communications network was developed in stages, using HF radio initially and gradually developing into the present private telephone network using LOS radio links and a troposcatter system.
The offshore industry is highly complex and demands specialized skills and techniques to ensure that production is maintained effectively and safely at all times. As the technology associated with offshore operations gain even greater complexity, offshore communications and information exchange systems become more and more important. Reliable communication is vital to ensure that offshore operations are constantly monitored and onshore efforts are well coordinated to support the offshore operations effectively.
Today's telecommunications technology offers the offshore industry a wide range of equipment including high frequency (HF), very high frequency (VHF), ultra high frequency (UHF), microwave and satellite systems. There is no standard package which can be employed. Each type of offshore operation has to be assessed in order to determine the most effective type of telecommunications system.
This paper discusses available telecommunication methods, factors affecting selection of an offshore system and a successful application of such methods by Esso Production Malaysia (EPMI) in their offshore communications network in Malaysia.
High Frequency (HF)- Radio has been the conventional means of communications for offshore operations especially in mobile operations such as exploration. This type of communication system has been employed because of its low cost and ability to cover long distances (up to thousands of kilometres). However, HF radio is highly susceptible to noise interference and variation of atmospheric conditions which frequently results in poor quality reception. There are many techniques for improving HF radio reception quality but many of them are not practical for offshore operations due to space limitation, restrictions on frequencies, or transmitter power.
Very High Frequency (VHF) Radio has been developed primarily for mobile communications of relatively short range (50–70 km). The exact range depends on transmitter power and antenna height. VHF radio is normally used for on-board platform communication (e.g., walkie talkies) and for mobile communication with workboats, supply vessels and helicopters. This type of radio is also used for fixed single channel point-to-point communication, e.g., between two fixed offshore locations or one fixed offshore and one on-shore locations or over a distance equivalent to that of line-of-sight (LOS) or slightly greater.
Ultra High Frequency (UHF) Radio has similar applications as VHF radio in mobile communications. In addition, UHF radio is frequently used for multi-channel radio link communication, where up to 60 voice channels can be multiplexed on one pair of frequencies. For offshore operations, UHF radio is normally employed between fixed locations because each UHF radio link is individually designed for point-to-point communication. The communications range is shorter than VHF radio, generally LOS. A number of UHF radio links may be connected together to form a multi-channel telephone network.
Microwave Radio is similarly used for multi-channel communication except that it operates at high frequencies (1–13 Ghz) and it can accommodate more channels (up to 2700 voice channels. However, because the antenuation of the propagation of radio waves over a fixed distance increases with frequency, microwave radio has a shorter range than UHF radio. Depending on antenna heights, the range of microwave radio link for offshore operations may be 30–50 km.
Troposcatter Radio is an UHF or a microwave radio that is used for trans-horizon (80–500 km) communications by forward scattering of radio waves in the upper tropospheric region of the earth's atmosphere. Troposcatter radio can be used for multi-channel communication of up to 300 voice channels. However, due to greater complexity, a troposcatter system is more costly and more difficult to install than a normal LOS UHF or microwave radio link. Therefore a troposcatter radio system is normally employed when an offshore operation requires a more reliable communication system than can be provided with an HF radio but the communication distance is beyond that of LOS radio links.
Satellite Communications technology has contributed to the enhancement of communication reliability and flexibility. There are many types of satellite systems available which fall under the categories of domestic, regional and international. Most satellite systems are of the geostationary type where a satellite orbits at about 35,800 km about the equator. The signal transmitted from an earth station is received, amplified by orbiting satellite and re-transmitted back to earth. The range of coverage of a satellite system exceeds 10,000 km. the advantages of satellite communication are that it can handle up to 12,000 voice channels and it enables multiple access from many earth stations within the coverage.
Fig. 1 illustrates the various telecommunications system discussed.
The selection of the types of telecommunication equipment for an offshore system depends on various factors, viz,
Type of offshore operation — Mobile operation such as exploration demand a communication system that is not affected by frequent changes of the operating location. This limits mobil operations to employing mobil HF, VHF or UHF radio or a satellite system. However, if an offshore operation is fixed, a multi-channel UHF, microwave or troposcatter system may also be used.