Where the target depth of any borehole is beyond the capability of the BGS remotely operated rockdrills, a drillship using wireline core-retrieval techniques is used. This method offers the ability to sample hundreds of metres below the sea bed. Wireline coring combines techniques developed by the oil and gas industry, mining and geotechnical coring tools, and the proven technology of wireline retrieval. BGS has developed and continually upgraded a suite of coring tools and interchangeable inner core barrels that have been successfully deployed on a range of projects
During wireline coring, an inner core barrel is dropped (under free fall) through the outer drill pipe, locking in place once it reaches the bottom of the drill string. When the coring operation to fill the inner core barrel is complete, a retrieval tool is lowered down the drill string on a wire (hence wireline). The tool locks on to the top of the core barrel, and on retraction releases the mechanism holding the barrel allowing it to be pulled back up the drill string to the surface. The advantage of this method is that different inner core barrels can be used to cope with varying geology.
The current inner core barrel options are:
The BGS 5m combined rockdrill and vibrocoring system offers the versatility of two sampling systems on one rig. This has the advantage of mobilising one system for a project that allows both hard rock (5m maximum) and soft sediment (6m maximum) to be sampled using the same system.
The RD1 system can be mobilised on any vessel of opportunity that has a Dynamic Positioning (DP) system and suitable A-frame. RD1 has been used for a number of scientific and commercial projects from the Antarctic to the Tropics.
The system can also carry a sub-sea video camera suite that assists accurate landing by having a real-time link to the operators on the vessel.
The BGS 55m Rockdrill (RD2), is one of our newest remotely operated sampling system. RD2 is capable of coring up to 55m below sea floor in water depths up to 4000m and is operated via its own launch and recovery system (LARS). The system can continuously core in 1.7m sections, and can be outfitted with additional sensors such as gas-flow meters and down-hole logging tools.
The RD2 system will be used in conjunction with the Bremen University (MARUM) MeBo sea-floor rockdrill on future International Ocean Discovery Program (IODP) expeditions implemented by the ECORD Science Operator (ESO).
The BGS RD3 system is small and compact and can operate in up to 2000m of water. The system is therefore suitable for operations on vessels where deck space is limited and is ideal for when working in shallow water where it is harder for large vessels to operate.
Having designed, built and operated vibrocoring systems since the 1970s, these are the BGS's oldest form of powered coring devices with a long and successful track record of recovering high-quality samples from various environments.
BGS currently has two Vibrocorer systems capable of coring either up to 6m or 3m of soft and unconsolidated sediment in up to 6000m of water. Sediments are collected in a plastic liner tube within a core barrel driven by a one-tonne weight and vibrator motor (hence the name vibrocorer) mounted at the top of the rig. Guillotine closure below the core barrel during recovery of the equipment aids in core retention during operations.
The systems are deployed using the vessel’s A-frame and either a ships lift winch, if using the battery-operated system, or the BGS umbilical winch for the full-powered version. Uniquely, BGS vibrocorers utilise a powered winch to extract the core barrel from below sea bed, prior to recovering the rig. This reduces the number of damaged core barrels and more importantly the strain on the lift umbilical.
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