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.
The Oriented Drill was specifically designed to recover samples for use in palaeomagnetic studies and was initially developed for use on the NERC funded BRIDGE Programme (British Mid-Ocean Ridge Programme; 1996-98) on the Mid-Atlantic Ridge.
The maximum core length is 0.8m and the system can acquire samples in up to 5500m water depth. Orientation is achieved by scribing the core along its length with a single reference line and then using the two drill-mounted compasses to assign a heading to this reference mark. This marking can subsequently be related to a world reference, thereby allowing detailed palaeomagnetic analysis to be carried out and to measure the orientation of crystals and fractures in rocks.
This drill is launched, recovered and operated by means of a standard scientific coax lift cable, found on most research vessels. This allows for easy installation on any suitable vessel. Due to the drill's small footprint there is minimal environmental impact.
The BGS Oriented Drill appeared on the front cover of the journal Geology in 2002.
The Gravity Corer is a simple coring system that can recover up to 6 m of core in soft sediments and has been successfully used in water depths of 3700m. It is run from a free-fall hydraulic winch with the potential to recover samples from 5000m water depth.
The system is supplied complete with winch, A frame and launch chute. The launch and recovery chute allows the system to be operated in adverse weather conditions. The system can be supplied with its own fully equipped workshop and core bench. Mobilisation can normally be carried out within 24 hours.
The box corer can be used to recover large volume sediment samples in any water depth that the vessel’s launch system can reach. The maximum volume of sample is 300 x 300 x 600 mm at full penetration. Small sample cores can be taken from side windows in the corer before the main sample is removed to the sample tray. The system is constructed from stainless steel to reduce the risk of contamination of the sample.
The system operates by means of a mechanical trigger once the corer has embedded itself in the sea bed. The corer is then recovered to the ship's deck using either an A frame winch and wire or a Hiab type crane and wire.
The Shipek Grab system is designed to recover small sea-bed surface samples of up to 2 kg. The system can operate in water depths of 300m. The grab operates by means of a hand priming system, which is set on the vessel. The grab is then lowered to the sea bed where, upon contact, a trigger weight on the grab strikes a release mechanism and the sample compartment closes to encapsulate a sample of sea-bed sediment.
An electro-hydraulic winch complete with metering system, is used to lower the grab to the sea bed on a 6mm wire at a speed of 60 to 70 m/minute. This allows the water depth at which the sample is taken to be recorded.
This system is ideal for taking a large number of small volume samples and is often used to take sediment samples in conjunction with other equipment on the same project.
The Clamshell Grab system can be used to recover large volume sediment samples from the sea bed (340 litres). This is a hydraulically driven mechanical grab that can operate in water depths of 70m. The system is supplied with a self-contained hydraulic powerpack and hydraulic winch. It can operate from any DP vessel or vessel at anchor. Sediments are recovered to deck where they are then released into an enclosed container for investigation. Sub-samples can then be taken from this container.
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