Drilling methods for different formations

Auger

Cheap and fast in dry formations

Cable

Good samples

Rotary mud

Fast penetration

Rotary air

Very fast in dry cohesive formations
Contamination of sample is possible

Rotary mud
reverse circulation

Good sample, fast penetration,
maintains wall conditions

Sonic

Fast, with good samples

Jetting

Cheap when plenty of water is available

Rotary

Air, water, or mud circulation, All give good results

Cable-tool

Good but slower

Hammer

Chip and water sampling, fast penetration

Diamond coring

Slower than hammer, produces excellent samples

Sonic

Fast, with good samples

Hammer drills

Fast penetration
• Top-hole hammer for shallow holes
• Downhole hammer in deeper holes

Diamond drills

Superior information and cores

Heavy rotary drills

Fast, cheap drilling if adequate bit pressure is applied

Eccentric hammer

For undercutting casing

Becker

Allows heavy casing driving

Cable-tool

Drives casing behind bit

Rotary reverse

Drills smaller boulders capable of circulation being lifted up the drill pipe

Sonic

Holds gravel and coarse sands in tube