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| Titel |
Simple, affordable, and sustainable borehole observatories for complex monitoring objectives |
| VerfasserIn |
A. Kopf, T. Freudenthal, V. Ratmeyer, M. Bergenthal, M. Lange, T. Fleischmann, S. Hammerschmidt, C. Seiter, G. Wefer  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2193-0856
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Instrumentation, Methods and Data Systems ; 4, no. 1 ; Nr. 4, no. 1 (2015-05-18), S.99-109 |
| Datensatznummer |
250115238
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| Publikation (Nr.) |
 copernicus.org/gi-4-99-2015.pdf |
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| Zusammenfassung |
Seafloor drill rigs are remotely operated systems that provide a cost-effective means to recover sedimentary records of the upper sub-seafloor
deposits. Recent increases in their payload included downhole logging tools
or autoclave coring systems. Here we report on another milestone in using
seafloor rigs: the development and installation of shallow borehole
observatories.
Three different systems have been developed for the MARUM-MeBo (Meeresboden-Bohrgerät) seafloor drill, which is operated
by MARUM, University of Bremen, Germany. A simple design, the MeBoPLUG,
separates the inner borehole from the overlying ocean by using o-ring seals
at the conical threads of the drill pipe. The systems are self-contained and
include data loggers, batteries, thermistors and a differential pressure
sensor. A second design, the so-called MeBoCORK (Circulation
Obviation Retrofit Kit), is more
sophisticated and also hosts an acoustic modem for data transfer and, if
desired, fluid sampling capability using osmotic pumps. In these MeBoCORKs,
two systems have to be distinguished: the CORK-A (A stands for autonomous)
can be installed by the MeBo alone and monitors pressure and
temperature inside and above the borehole (the latter for reference); the
CORK-B (B stands for bottom) has a higher payload and can additionally
be equipped with geochemical, biological or other physical components. Owing
to its larger size, it is installed by a remotely operated underwater vehicle (ROV) and utilises a hot-stab connection
in the upper portion of the drill string. Either design relies on a hot-stab
connection from beneath in which coiled tubing with a conical drop weight is
lowered to couple to the formation. These tubes are fluid-saturated and
either serve to transmit pore pressure signals or collect porewater in the
osmo-sampler. The third design, the MeBoPUPPI (Pop-Up
Pore Pressure Instrument), is
similar to the MeBoCORK-A and monitors pore pressure and temperature in a
self-contained manner. Instead of transferring data on command using an
acoustic modem, the MeBoPUPPI contains a pop-up telemetry with iridium link.
After a predefined period, the data unit with satellite link is released,
ascends to the sea surface, and remains there for up to 2 weeks while
sending the long-term data sets to shore.
In summer 2012, two MeBoPLUGs, one MeBoCORK-A and one MeBoCORK-B were
installed with MeBo on RV Sonne, Germany, in the Nankai Trough area, Japan. We
have successfully downloaded data from the CORKs, attesting that coupling to
the formation worked, and pressure records were elevated relative to the
seafloor reference. In the near future, we will further deploy the first two
MeBoPUPPIs. Recovery of all monitoring systems by a ROV is planned for 2016. |
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