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FP5

METROL Sintesi della relazione

Project ID: EVK3-CT-2002-00080
Finanziato nell'ambito di: FP5-EESD
Paese: Norway

ROV derived video data and seismic data from Gullfaks, Tommeliten and Nyegga, physical and biological effects of hydrocarbon seeps in northern waters

Result description:
Since the early 1980's Statoil has conducted research on seepage of hydrocarbons in northern waters. The current METROL initiative (2002-2005) was incorporated as part of this endeavour.

Main results from the Statoil/METROL work show that:
- Both micro- and macro-seeps are self-sealing, where the formation of bacterial mats and carbonate represent major steps in the sealing process,
- Focussed hydrocarbon seeps are long-lived and reach a steady-state flux situation,
- Bacterial mats are used as nutrients to macro organisms (hermite crabs),
- Large amounts of carbonate can form sub-surface,
- Hydrate-pingoes modify the seabed topography.

'Hydrate pingoes' form part of this landscape. They are up 1 m high mounds and have four main characteristics:
- They are sediment-covered
- They have a 'carpet' of tubeworms
- They are partly covered by bacterial mats
- They have 'corrosion pits' where soil has become fluidised.

Hydrate pingoes only form at locations where there is a continuous supply of 'guest molecules' from below (i.e., where there is seepage of light hydrocarbons). They are a direct result of local formation and disintegration of sub-surface gas hydrates.

ROV-operations:
During METROL methane bubbling through the seafloor at Tommeliten and Gullfaks was detected by the use of hull-mounted single beam echosounder. ROVs were used to document these 'macro' seeps visually on the seafloor. In addition to visible macroseeps, there also occurs 'invisible' microseepage of fluids through the seafloor. These are very difficult to document without the use of ROVs. At Nyegga there are only microseeps. At microseep locations which occur at all sites Tommeliten, Gullfaks and Nyegga, bacterial mats form on the seafloor due to anoxic water flowing up to the seafloor.

ROV-operations conducted by Statoil at the three sites resulted in the visual documentation of the exact location of bacterial mats and microseepage. These ROV-operations have been conducted using dynamically positioned (DP) operated surface vessels and high accuracy underwater position keeping.

Key innovations:
Key innovations are that hydrate pingoes and bacterial mats show the exact locations where active micro-seepage occurs.

At Nyegga, we have for the first time documented the existence of a gas hydrates submarine 'tundra' landscape on the seafloor. The very irregular landscape is suspectedly caused by the formation and disintegration of sub-seafloor gas hydrates, much in the same fashion as sub-surface ice in a true tundra landscape on land.

Current applications:
The results help Statoil and other users of the seafloor to improve our field development strategy and designs, and to improve our understanding of the natural chemical environments and their effects on biology.

Users:
All the results are utilized by Statoil to improve the knowledge on the hydraulics of the seafloor in association with field development and pipeline construction.

Further users interested in these results are: engineers, exploration geophysicists, biologists, environmental and drilling safety specialists, marine geologists.

Expected benefit:
Statoil scientist working within METROL is an advisory member of the IOPD committee since 1986, funded by Texas A&M University, and esp responsible for safety problems in drilling. METROL results are expected to feed into increased safety and improved environmental issues (less impact) in drilling, as it becomes more and more know, which pockets can be drilled into and which are too dangerous and should be left alone.

Reported by

STATOIL ASA
Forusbeen 50
STAVANGER
Norway
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