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As terrestrial sources of oil diminish, the oil industry has moved its exploration further and further offshore in their quest for new fields. Whilst much has been learned over decades about sub-sea production from near-shore sites such as Gulf of Mexico, North Sea, Black Sea and Australia, new problems are being encountered as exploration moves further offshore.
If the forecast holds true that known oil reserves will run out within 40 years, then exploitation of deep-sea methane hydrates may take the industry into waters over 4 kilometres deep. All this has resulted in a greater demand for oceanographers to help in overcoming a range of problems.
Environmental Assessment
Environmental impact assessment has become an essential component of any new sub-sea activity. The establishment of 'baselines' for the chemistry, biology and geology of proposed new sites, together with ongoing monitoring of conditions, calls for a wide range of marine scientific expertise and techniques. A recent survey carried out by the Southampton Oceanography Centre (SOC) on the continental slope of the Faeroe-Shetland Channel demonstrated the oceanographers' skill to integrate data from various scientific disciplines to produce a complete picture.
The remit, on behalf of The Atlantic Frontier Environmental Network (AFEN), was to undertake a baseline survey of the sea-bed environment over 20,000 square kilometres in water depths from 120 to 1500 metres. The survey included sea-bed mapping with side-scan sonar, sediment sampling, seafloor photography and fish trapping. A key feature of this package was the integrated nature of the survey whereby the side-scan data were used to help plan the sampling programme and then the samples and photographs were, in turn, used to 'groundtruth' the side-scan data. Specialised oceanographic equipment used included; Towed Ocean Bottom Instrument (TOBI), OceanCam 6000 (deep-sea stills, time-lapse and video cameras) and Bowers and Connelly Sediment Multiple Corers. This equipment allowed detailed information to be drawn up, particularly about the chemistry and biology of the surficial sediments and will continue to be useful for subsequent sampling and monitoring.
Installation of Pipelines
Offshore oil production presents problems in the transport of oil to land-based storage and treatment plants. Transportation using surface vessels is expensive and time-consuming, so the installation of pipelines is favoured. However, the installation of such pipelines requires specialist skills and calls upon the oceanographer to help minimise the risks. Such an example is the deployment of pipelines to North Sea oil platforms by an Aberdeen based company, Rockwater Ltd, who launch pipeline 'bundles' from their onshore fabrication facility at Sinclairs Bay, in the north of Scotland.
Rockwater are currently building onshore bundled pipelines in up to 7.5km sections for use in field operations, launching them, ballasting them to neutral buoyancy, towing them out to a field in mid water and installing on location, reducing field development time. Rockwater have utilised the skills of oceanographers to build up a picture of the physical conditions in Sinclairs Bay in order to minimise the risk of downtime, during a pipe bundle launch. The model is to be used for future bundle launches during and prior to deployment to predict the current speed and direction in the bay, positions of eddy formation etc. This information is critical in determining the timing of the deployment and the vessels required during the launch/ tow out.
Arrays of current meters were distributed across the bay on moorings, designed and deployed by SOC technicians, and the data was incorporated into a predictive mathematical model by scientists at the Proudman Oceanographic Laboratory (POL). Rockwater will continue to operate an end-user programme from this model prior to all bundle launches in this area. Sinclairs Bay is a shallow in-shore area, but one of Rockwater's next projects will be to lay pipes to oil wells in much deeper waters (up to 1500 m) off the coast of Brazil.
Deep-sea Surveillance
Sub-sea pipelines, once laid, can still present problems in terms of regular inspection. Deep-sea surveillance has long been successful for academic research activities, particularly marine biology, but those same time-lapse cameras could very soon find a role in surveillance. A specialist deep-sea camera produced for this purpose by SOC is the OceanCam 6000. It is an intelligent, programmable 35mm camera system which allows the operator to pre-set time intervals for photography.
Housed in a resistant pressure case with a high-power flash unit and battery pack, these cameras have been used to monitor the biological activity on the sea-floor in over 4 kilometres of water for periods up to two years. Such cameras may soon find a role in monitoring sub-sea pipelines and tailings from oil wells. An important feature of pipeline monitoring is the prevention and control of corrosion, particularly where the pipe is lying in anoxic, sulphur rich sediments. A recent development by SOC, of a Bowers and Connelly Multicorer, was used to sample the gas in sediments close to a sub-sea pipeline in order to assess the corrosion potential. |
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Deep-sea Engineering
Sub-sea oil wells do, in themselves, present new challenges in engineering for the oil industry. Structures which sit on the sea-bed in deep-water sites must withstand the high pressure (10,000 p.s.i. at full ocean depth) and low temperatures (typically 2 - 4oC) and of course prohibit the ingress of seawater or the escape of oil. The remote nature of the sea-bed also places higher demands on the long-term reliability of the equipment. One operation designed to improve efficiency is the sub-sea separation of oil and water. Present systems involving transport to surface in ships is time-consuming and costly. Whereas sub-sea separators would allow oil to be brought to the surface whilst the water can be re-injected into the well. The success of such a separator depends heavily on monitoring the efficiency of the unit by measuring the quality of oil in the separated water. This requires the installation of an in-situ oil-in-water meter (OIWM) which will telemeter data to a control station at the surface. Currently, a deep-ocean optical instrument is being developed, to measure dispersed oil in production water in the pipeline.
The oil industry meets oceanography in somewhat unexpected ways too; for example the identification of free water in oil cargo. In a case recently, Ocean Scientific International Ltd., were able to identify the source of free water in an oil cargo using their oceanographic expertise. As a result, a claim in excess of $2m was settled in favour of the client for loss of oil cargo.
Oceanography has developed significantly over the past 50 years as more sophisticated instrumentation (particularly computers and satellite) has become available. The oil industry has seen large improvements in its efficiency during that period too. As the need develops to exploit more off-shore oilfields, with an emphasis on efficiency and cost-saving, the worlds of the oil man and the oceanographer are coming even closer and both should benefit from this synergy.
By Paul Ridout, Managing Director, Ocean Scientific International Ltd.
Published in Sea Technology April 1999
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