Simple, Affordable and Sustainable Borehole Observatories for Complex Monitoring Objectives
Abstract: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. We here report on another milestone in using seafloor rigs: The development and installation of shallow borehole observatories.
Three different systems have been developed for the MeBo seafloor drill, which is operated by MARUM, Univ. 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, is more sophisticated and also hosts an acoustic modem for data transfer and, if desired, fluid sampling capability using osmotic pumps. Of these MeBoCORKs, two systems have to be distinguished: The CORK-A (A = 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 = 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 ROV and utilises a hotstab connection in the upper portion of the drill string. Either design relies on a hostab connection from beneath 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 pore water in the osmo-sampler. The third design, the MeBoPUPPI ( In 2012, 2 MeBoPLUGs, 1 MeBoCORK-A and 1 MeBoCORK-B were installed with MeBo in the Nankai Trough, Japan, and data were successfully downloaded from the CORKs.
In 2012, 2 MeBoPLUGs, 1 MeBoCORK-A and 1 MeBoCORK-B were installed with MeBo in the Nankai Trough, Japan, and data were successfully downloaded from the CORKs.