REVERSE CIRCULATION DRILLING

HOW IT WORKS?

In RC drilling, a driller needs to use enough air pressure and rotating force to a drill string composed of a bit, pneumatic hammer assembly and a series of pipe with inner and outer tubes to create percussive energy required to produce rock chips which are returned to surface inside the rods.

 

Application Used for bulk commodities where a broad definition of the body and geochemistry analysis are important
Sample quality Very approximate results through rock chips analysis
Drilling speed Fast penetration rates depending on the ground conditions, but usually 200m per shift
Hole depth The hole’s depth depends on the capabilities of the drilling rig, but typically 800 m with large rigs and high pressure boosted air
Hole size 89 to 146 mm
Flexibility Taking into account the ground geological characteristics and choosing accordingly the right range of tools, remains still limited where open hole drilling is possible
Cost Higher initial investment, but thanks to the high drilling speed costs are lower until hole depth require higher pressures.
Time It is not a time consuming as drilling is done fast
Technique A drill is required to produce the rotation and pressure needed to drive a string of tools consisting of a bit  which rotates at high speed, cutting through the fresh rock, pneumatic hammer assembly and a series of pipe with inner and outer tubes. Water is also used for lubrication, cooling, and removal of drill cuttings from the hole.
Challenges The main challenge related to RC drilling is providing a large inner diameter through the drill pipe to allow easy retrieval of core barrels and surely, the drilling operations in a limited space

 

Drill Structure

Reverse Circulation drilling is so called because it uses dual-wall tubes. The compressed air travels trough the outer wall of the drill pipe to the hammer assembly where it drives a piston up and down between inner and outer spaces.

The air is discharged through ports which are opened and closed as the piston moves through its cycle at a rate up to 2000 rpm. The piston transfer to the bit enough energy to break the rock.

The broken chip sample is air lifted by the discharged air up to the surface through the inner tube of the drill pipe.

There standard tube sizes associated with specific thread:

  • From 89 mm to 114 mm

The drill size used depends on the desired hole diameter and the desired depth of drilling, and the wider the diameter of the tube, the more power that is required to drive the drilling.

The most popular threads are:

  • REMET
  • METZKE