BG Tunisia boosts offshore communications capacity

By 4RF

Background
With the Miskar gas field in the Gulf of Gabès supplying some 80% of Tunisia’s gas requirements – and estimated to have enough reserves to meet the country’s needs for around ten years – security and continuity of supply are strategically vital. For the operator of the gas field BG Tunisia, therefore, reliable voice, data and video communications between the Miskar offshore platform and its onshore operations are a must. However, with 125 km of sea, highly variable atmospheric conditions and large, moving structures to contend with, providing a reliable connection cost-effectively is no easy task.

BG Tunisia objectives
BG Tunisia has a 100 per cent interest in the offshore Miskar gas and condensate field, as well as interests in two exploration permits in the area. Its gas sales contract with the Tunisian State electricity and gas company, Societé Tunisienne de l’Electricité et du Gaz (STEG), gives it the right to supply over 230 million standard cubic feet of gas per day (mmscfd). During its lifetime, it is estimated that the Miskar field will produce more than 700 billion cubic feet of sales gas.

Sixty-two meters under the sea, and 125km out in the Gulf of Gabès, the Miskar gas field covers an area of 352 sq km. Sour gas from ten wells is sent through a sub-sea pipeline and processed at the Hannibal plant 20km south of Sfax.

Gas production parameters at the Miskar platform need to be continuously monitored. This is not only to ensure successful co-ordination between the offshore platform and the onshore storage and processing plant, but also to ensure that production targets and contract terms are being met.

Prior to working with 4RF, BG Tunisia was using an analogue radio connection between the Miskar platform and the coast. This had a maximum data throughput of 9.6 kbit/s, and frequently the dialup connection would go down, meaning data would not only travel very slowly, it would frequently have to be resent. BG Tunisia knew it needed more capacity to provide faster, more reliable data connectivity – for email, web access and applications like enterprise resource planning (ERP), as well as telemetry – and to handle real-time PBX telephony and video communications.

4RF approach
4RF needed to employ all its radio engineering expertise to provide BG Tunisia with a solution that would meet all its requirements reliably and cost-effectively. An experienced team from 4RF advised on path engineering, systems design, integration, and frequency planning.

There were several tough challenges to overcome. First of all, the gas platform itself is a continuously flexing object: any radio solution would have to be able to cope with the continual movement of the sea. Second, the Gulf of Gabès is an area of extreme temperatures: extremely hot during summer days, with much lower temperatures during the night and in winter, giving rise to unusual atmospheric conditions that alter the curvature effect over the sea and cause significant fading. Third, the distances involved are long, and there is a limit on the height of metal structures because of safety regulations.

The solution
To simplify the engineering task, 4RF deployed a three-hop sea path solution to Miskar, using the Ashtart platform and the Isles of Kerkennah for repeater points. Aprisa SE point-to-point digital microwave radio transmission systems provide these three maritime hops and connect the onshore station at Guebiba Tower to the Hannibal plant and to the public telephone exchange at Sfax.

Thanks to the Aprisa SE system’s carrier-class performance and in-built flexible interfaces, BG Tunisia is able to combine its voice, data and video traffic efficiently into a common narrowband RF channel. Telephony and video traffic is carried using fractional E1 interfaces, while the data traffic is carried over a 256 kbit/s Ethernet interface. The Ethernet interface can be easily upgraded to 512 kbit/s, or higher, capacity.

As well as delivering the technical solution, 4RF provided commissioning, technical support and optimization services to ensure that BG Tunisia’s solution delivers the best possible performance.

The results
BG Tunisia now has a robust, high-capacity link to carry all its voice, data and video traffic between the Miskar platform and it onshore facilities. Traffic is not only handled faster and more efficiently, it is also less prone to errors – thanks to high-gain antennas, transversal adaptive equalizers that boost signal strength, and smart forward error correction (FEC) procedures – as well as having 1+1 standby link protection.

Summary
The robust, efficient radio transmission solution provided by 4RF means that BG Tunisia can monitor and manage production at the Miskar platform closely. This enables the company to match production very precisely with demand, and to ensure that it is meeting its targets and commitments accurately.

Safety, accessibility and quality of life are also improved for those who work on the platform.