GeoMEM Solutions: Core Orientation

Core orientation is a method of measuring the orientation of the length of rock that is cored when drilling.

Usually core orientation is achieved by fitting a device or instrument above the core barrel (some may fit within it) that records its own rotational angle (relative to vertical) when the core is broken off by teh driller. When the rock core is recovered the recorded angle in the tool is used to orientate the core into the postion it was in when it was in situ.

This information, together with borehole survey information, provides an accurate orientation of the core in 3D space. This in turn allows the correct location in 3D of any and all linear features in the rock and so allows accurate modelling of the rock structures, lithological features and/or mineral deposit.

Core orientation devices are amongst the earliest of instruments that were developed for borehole use – having been recorded from the 1840’s (170 years ago).

A single instrument involves running the instrument with the core barrel, recording the angle, breaking core, retrieving the core barrel and instrument then orientating the core at surface before restarting/attaching the tool to a core barrel to repeat the process. This involves a delay (usually a few minutes) in drilling whilst the orientation is made at surface. In some projects this time may not be important but, in others, this delay may add up to be an important consideration when many core runs are being made. Mistakes may be made when the person measuring the core orientation feels under time pressure to get the reading.

The simple solution to this is to run two Core Orientation instruments in parallel: One instrument is run and retrieved whilst the other is used to get the previous runs core orientation and is prepared for its next run. In this way, as soon as a core barrel has been retrieved, another core barrel and core orientation instrument are ready to run and the core orientation of the previous run can be obtained whilst the drill string is lowered and the next length of core is drilled. This results in faster turnaround and more efficient use of time and resources.

GeoMEM supplies two DEVICO DeviCore Core Orientation systems:

  • DeviCore II: A single mode instrument.
  • DeviCore BBT: Dual mode system using two instruments with Brilliant Blue Technology (BBT) - a fast and efficient Bluetooth connection.

These systems are available for both sale and rental and fit in core barrels or rods with inner diameters from 37mm upwards.

 

See also: Borehole surveying, Directional drilling