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The
discovery of oil in the North Sea in the 1960s resulted in the
construction and installation of large offshore structures needed
to develop the new-found oil fields.
The reverse process of removing these enormous structures has
recently become an important activity in the North Sea.
On June 27, 2001 the gravity based Maureen Alpha
Platform, located in the Maureen Field at the U.K. Continental
Shelf Block 16/29a, was successfully removed and towed to the
western coast of Norway for demobilization and possible
re-use.
The Maureen Alpha platform is a steel gravity base structure with
a weight of 112,000 ton, height of 241 meters and steel skirts for
penetration into the seabed.
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The first millimeters of the
breakaway from the seabed during the initial re-ballasting and
re-float operations were extremely critical, and the Norwegian
Geotechnical Institute (NGI) was given the job to deliver a
monitoring system with the necessary accuracy for measurement of
the vertical elevation between the structure and the seabed.
NGI has solved specialized instrumentation tasks offshore
for more than 30 years based on their experience with heavy
fluid systems and the ultra accurate Digiquartz
Pressure Sensors from Paroscientific Inc.
NGI
designed three recoverable systems that in fact measured the
vertical elevation with an accuracy of less than one millimeter
for a range of over 10 meters at a water depth of 96 meters.
All units were successfully installed by divers, and
recovered to surface after use.
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