20 years of operational experiences with the MARUM-MeBo sea floor drill rigs: scientific applications and lessons learned

The sea floor drill rig MARUM-MeBo is a robotic drill rig that is deployed on the sea floor in order to collect cores from sediments and hard rocks. It can be deployed from multipurpose research vessels. The first generation MeBo70 was designed to drill down to 70 m below sea floor (mbsf) and is operated for about 20 years since 2005. The second generation MeBo200 had its first deployments in 2014. So far, a maximum drilling depth of 146 mbsf was reached. In summary, we have conducted 30 research expeditions and drilled 7465 m. Core recovery rates were in average about 67 % and strongly depend on the drilled lithology. A better control on flush water circulation by using a mud mixing system will be needed to improve the drilling results especially in sandy deposits and crystalline rocks. Knowledge on the expected geology combined with a hydroacoustic survey including high resolution bathymetry in rough terrain, high resolution seismics and sub-bottom profiling are needed for safe operations and optimizing the drilling strategy. A variety of research targets were addressed during the drilling campaigns with MeBo including paleoenvironmental research, gas hydrates and associated processes like authigenic carbonate and pockmark formation, slope stability, geothermal gradient and fluid circulation as well as mafic and ultra mafic rock alteration. Next to core drilling, the sea floor drill rigs are used for bore hole logging and the installation of instrumented borehole observatories.