communication. The MeBo uses the modular


Digital Telemetry System for subsea robotic devices from Schilling Robotics. This company also devel- oped the loading arm and the rotating magazines that are used for storage of the required drill tools on the rig. Prakla Bohrtechnik was responsible for the drill technology and the hydraulic design. Robotic sea-bed drill rigs


have several advantages com- pared to drilling vessels, espe- cially when only shallow drilling is required. Sea bed drill rigs are not af-


fected by any ship movements due to wind or waves. Since they operate from a stable plat- form on the sea bed, optimal control of drill-bit pressure can be achieved, which is prerequi- site for optimal core quality.


The MeBo200 concept The MeBo 200 is the next evo- lution of the successful MeBo, developed and manufactured under the supervision of Marum, with enhanced appli- cation parameter, such as de- ployment (4,000m) and drilling depth (200m) (Fig. 1). Marum and BAUER Maschinen are collaborating in developing an upgraded MeBo 200 system – based on the ex- perience during development and operation of the MeBo drill rig.


The MeBo200 will weigh


about 10 tonnes. The maga- zines will have an increased storage capability for drill rods and core barrels (96 slots in- stead of 68). The length of the core barrels will be 4.7 m. Core barrels for a core di- ameter of 54 - 63 mm will be used. Four legs are extended be-


fore landing to increase the sta- bility of the rig and leveling due


to possible unevenness of the sea bed.


MeBo200 uses the wireline


core drilling method (optional). This method is most commonly used for mineral exploration drilling where undisturbed core samples are essential for under- standing the structure of the de- posits.


The mast with the feeding system and the power swivel forms the central part of the drill rig. It is mounted on a guide carriage that moves up and down the mast with a max- imum push force of 5 tons. A water pump provides sea water for flushing the drill string, for cooling of the drill bit, and for drill cuttings removal. The sys- tem utilises rotary core barrels with diamond or tungsten car- bide bits.


Possible applications of the MeBo 200 The current MeBo 200 can be adapted for applications other than coring for scientific pur- poses. A possible use of the MeBo 200 could be for the ex- ploration or pilot production tests of submarine gas hydrate deposits. Gas hydrates are ice-like crystalline systems made of water and methane that are sta- ble under high pressure and low temperature conditions.


Offshore Technology November/December 2012


First concept of the MeBo 200


morphology of gas hydrate sed- iments that can be encountered. Hence, it is likely that no


universal drilling formula can be developed, but understand- ing gas hydrate behaviour while drilling will help reduce the in- herent risks and improve the process.


MeBo 200 can be used as drilling rig in order to start pilot production boring. However, further development is cur- rently needed in order to apply the drilling rig for such opera- tions.


Gas hydrates deposits are located within a mid-depth zone around 300–500 m thick in the sediments (the gas hy- drate stability zone, or GHSZ) where


they coexist with


methane dissolved in the fresh, not salt, pore-waters. Above this zone, methane is


only present in its dissolved form at concentrations that de- crease towards the sediment surface. Below it, methane is gaseous. At Blake Ridge on the At- lantic continental rise, the GHSZ starts at 190m depth and continues to 450m, where it reaches equilibrium with the gaseous phase. Measurements indicate that methane occupied 0-9% by vol- ume in the GHSZ, and ~12% in the gaseous zone. Gas hydrates have been identified as strategic resources and may surpass all known oil and gas reserves combined. However, these resources will become reserves only if the gas contained therein can be pro- duced economically. To drill wells in a gas hy-


drate formation, a conductor casing is needed to allow close loop circulation of the mud, if different from seawater. How- ever, drilling through gas hy- drate becomes increasingly difficult due to the variety of the


A platform can be installed on the submarine seabed. This is connected to a conductor pipe. Axial conduit and produc- tion pipes are sunk and con- nected to the conductor pipe. The forces are transferred to the platform.


In the case free gas bub-


bles are encountered the plat- form might be connected to the soil with helical piles. The stability force depends on the mechanical properties of the soil and this is unknown yet. Alternatively, a blowout pre- venter might be installed be- tween the guide base and the MeBo.


The conductor pipe might


be driven by means of ham- mers, the MeBo will be de- ployed, and axial conduits are released. The MeBo is recov- ered and the BOP might be re- leased. MeBo is again deployed, production casing will be in- stalled by means of the drill rig and the MeBo is recovered to the vessel.


The MeBo 200 can be also modified and used for the min- ing of marine sulfide deposits, which are mainly located in mid-ocean on the East Pacific Rise, the Southeast Pacific Rise and the Northeast Pacific Rise, and searching for minerals (e.g. diamonds) in a marine envi- ronment.


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