Most existing LoFS systems rely on electronics to transmit data from the seabed receivers, through an array of seabed cables to the recording system, which is typically located on an offshore platform. High voltages are generally required to ensure an adequate power supply throughout the network of electric cables, which can be several hundreds of kilometres long. Electrical systems are prone to failure in a harsh subsea environment, particularly at vulnerable parts of the network such as cable connections. In addition, many active electrical components have a relatively short expected operational lifetime. Recovery, maintenance and/or replacement of failed electrical subsea equipment is time-consuming and expensive, which is a key reason for the, as yet, slow adoption of LoFS by the oil and gas industry.

The benefits of fibre-optic solutions Fibre-optic seabed sensor and cable solutions bring a new level of reliability and cost-effectiveness to LoFS. The telecommunications industry has been crossing the oceans with fibre-optic cable for decades, and an increasing range of fibre-optic solutions are being deployed in oilfields, including well monitoring, coil-tubing applications and surveillance of subsea equipment. Passive fibre-optic seismic systems avoid dependence on in-sea electronics so are inherently more reliable. The first company to adopt fibre-optic technology for a LoFS project was ConocoPhillips, for its Ekofisk field. Fosar – through-life, cost-effective PRM All subsea components of the high-fidelity Fosar seismic PRM solution from Stingray are passive fibre-optic, with no potentially unreliable in-sea electronics. The system leverages developments in the international telecoms market to minimise the cost of components, combined with a unique proprietary solution to combine large numbers of sensors onto a small number of optical fibres, minimising the size and complexity of the subsea array and associated platform-mounted interrogation system. The result is a highly cost-effective, reliable and lightweight LoFS system that is easy to install, operate and maintain throughout the life of a field. *see The Leading Edge; December 2008; v. 27; no. 12; p. 1632-1637; DOI: 10.1190/1.3036967

Fosar® is a cost-effective and reliable permanent reservoir monitoring system. Click to view