Video Transcript
The differences between the air rotary system and this drilling system are primarily the cutting action and the resulting cuttings, as shown. The down- the-hole hammer uses the rotary percussion cutting action through the use of a button bit. This system is best suited for well consolidated formations, offering excellent penetration rates. Compressed air provides the percussive energy to power the hammer. The resulting exhaust removes the cuttings. Note the quality of the cuttings. They are large, clean, and unmasked, representatives of the geology. Water only is added to the air to assist with both, cuttings removal and suppressing dust. This results in an aquifer, which requires minimal time to develop.
The example in the video (0:51) utilizes a chalk line to show the correlation between penetration rates and drill string rotation. This example is relevant to a six inch hole diameter only. First too slow rotation for the geology is represented by the wide space in between chalk lines. Next, is correct rotation speed, as shown by approximately three-eights inch spacing between chalk lines. Finally, excessive rotation speed is shown, as noted by minimal spacing between chalk lines.
