GEOTECHNICAL/ENVIRONMENTAL STUDIES

Imperial College, London has just completed a project concerning the geotechnical properties of seabed sediments. The study, part-funded by the UK's Health & Safety Executive, comprised: development of a computer-based control/data acquisition system and an improved local strain instrumentation system for a large hollow cylinder apparatus performing proving trials with the apparatus followed by experiments to assess the shear-strain and shear strength anisotropy of a quartzitic silt.

West of Shetland, NW Norway seabeds under analysis

Imperial College, London has just completed a project concerning the geotechnical properties of seabed sediments. The study, part-funded by the UK's Health & Safety Executive, comprised:

  • development of a computer-based control/data acquisition system and an improved local strain instrumentation system for a large hollow cylinder apparatus

  • performing proving trials with the apparatus followed by experiments to assess the shear-strain and shear strength anisotropy of a quartzitic silt.

Parallel programmes supported by Amoco, the Marine Technology Directorate and the UK's Building Research Establishment involved stress-path triaxial, hollow cylinder and resonant column experiments on clay-silts and sands from Pentre and Dunkirk. At both these sites offshore piling studies were undertaken via large-scale joint industry projects.

Nearly all offshore foundation problems and submarine slope failures are influenced by rotations of the main stress direction. But the effects of these rotations on natural, anisotropic soils are difficult to assess, and in fact are often neglected. Imperial College's programme focused on dense quartz silt, for which no data had previously been compiled.

HSE hopes this type of research will improve understanding of soil slope failure predictions and the effects on the design of bottom-founded structures and pipelines, particularly in new development areas such as the sensitive silty deposits West of Shetland.

Southampton Oceanography Centre, also in the UK, is spearheading another new project, called Poseidon, which groups together a multi-disciplinary team of European scientists. Their aim is a detailed survey of the seafloor in and around the Storrega Slide, a well-known submarine slide area off Norway's north-west coast.

According to project coordinator Dr Angus Best: "We hope to develop a European capability for measuring, mapping and monitoring deep-sea sediment stability. In order to do this we will have to develop new techniques for obtaining high resolution images of the sea floor, and gathering information on the type and organisation of sediment present."

The team's first step will be to design and build deepwater instruments for studying slope instability. A scatterometer will be developed at Southampton to investigate how the ocean floor around the Storrega Slide reflects sound, and thereby determine what type of sediment the sound bounces back from.

Although most slides around the world are triggered by earthquakes, said Dr Best, there is evidence that the build-up of gases within the sediment may influence slide initiation in the Storrega region.

Once the instruments are ready, the research team will map and monitor the 3D structure of the upper sediment layers and determine the sediment's physical properties. Results will be incorporated into a database for easy access and manipulation of slope stability data. In addition, laboratory experiments will be performed in large water tanks to mimic the behavior of sediments in slope failure and to integrate the acoustic data with actual observations. These experiments will determine the effect of methane gas liquefaction on slope stability.

In a separate environmental study, Sothampton Oceanography Centre is examining the importance of `marine snow' on the seabed ecosystems West of Shetland. Small organic particles on the ocean surface with negligible sinking rates develop into rapidly sinking aggregates that reach the seabed in a few weeks. Once there, they form a carpet of material sometimes 1cm thick (marine snow).

However, West of Shetland the effect of complex current systems on this process is unknown. In the upper 500 metres of the sea in this region, water moves in a north-easterly direction, while in the lower waters flow is usually south-westerly. The movements in opposite direction cause turbulence, which in turn increases collision rates between particles, affecting rate of formation and marine snow deposition and hence any marine life that feeds on it.

Southampton has just completed the first part of a mapping survey of the seafloor in this region. Under the next phase, Bathsynaps underwater time-lapse cameras will be used to record seabed changes and their effect on the biological communities. This data will be analysed with sediment samples collected from selected areas.

The project will be of interest to oil companies operating West of Shetland. Last month the inaugural meeting of the Atlantic Frontier Environmental Forum was held in Aberdeen: its main function is to hold informed discussions on the environmental aspects of Atlantic Frontier activities, as well as examining funding for projects relevant to possible environmental impact in Shetland, Orkney and other areas.

Britain's Royal Society for the Protection of Birds welcomed the new forum, as the waters in this area are feeding and breeding grounds for gannets, puffins, guillemots, fulmars, storm petrels, Leach's petrels, and the world's largest colony of great skuas - all highly susceptible to oil pollution. The effectiveness of local spill-combat facilities in this new frontier region has been questioned recently by environmental pressure groups.


Floating production supergroup formed in Norway

Aker Oil and Gas Technology and Maritime Group have combined to form a new company, Aker Maritime. The new group will have combined turnover of NKr10 billion turnover and 9,400 employees worldwide, and the aim is to keep growing, partly through further mergers or takeovers.

Head office will be Oslo, with Kristiansand the centre for activities related to production ships and other products. Maritime is particularly strong in floating production vessels, while Aker has expertise in TLPs, semisubmersibles and Spar platforms. No downsizing will be involved.

One project the new group will be watching closely is oil production from Norsk Hydro's Troll West gas province, where 736MM bbl in layers 12 metres thick below the gas cap are thought to be recoverable. Under a PDO to be submitted to the Norwegian authorities next month, Hydro aims to extract the oil via 62 horizontal wells, including 30 in the southern area tied back to the existing Troll B platform through five subsea well clusters.

The northern section will be drained via 32 wells tied back to a new Troll C production platform, likely to be a catenary-moored semisubmersible - again with five subsea clusters. Daily production capacity will be 126,000 bbl, while B's platform will be upgraded to output 252,000 bbl daily.

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