DRILLING KNOWLEDGE
1.1 ELEMENTS OF DRILLING PROCESS
1.2 PERCUSSIVE DRILLING
PRINCIPLE OF PERCUSSIVE DRILLING
PRINCIPLE OF ROCK BREAKAGE
1.2.1. Typical problems in percussive drilling
1.2.1.1 PERCUSSION
TOO HIGH:
- BUTTON BREAKAGES
- DRILL STEEL/ SHANK BREAKAGES
TOO LOW:
- LOW PENETRATION
- EXCESSIVE BUTTON WEAR
- (DUE TO ROTATION BREAKING THE ROCK) -> PERCUSSION MEASURE SETTINGS ARE ALWAYS COMPROMISE BETWEEN PENETRATION RATE AND DRILL STEEL ECONOMY
1.2.1.2 FEED
TOO HIGH:
- DIFFICULTIES IN FLUSHING
- RAPID BUTTON WEAR/ BODY WEAR
- INCREASED HOLE DEVIATION
- DIFFICULTIES IN UNCOUPLING
- BENDING OF DRILL STEEL AND SHANK -> BREAKAGES
TOO LOW:
- BUTTON WEAR AND POOR PENETRATION
- LOOSE COUPLINGS AND EXCESSIVE THREAD WEAR
- POOR ENERGY TRANSMISSION
1.2.1.3 ROTATION
TOO HIGH:
- RECUTTING AND LOW PENETRATION RATE
- EXCESSIVE BIT WEAR {SINCE THE ROCK IS FORCED TO BREAK BY ROTATION INSTEAD OF PERCUSSION)
- UNCOUPLING IS DIFFICULT
TOO LOW:
- LOW PENETRATION RATE
- ENERGY IS LOST FOR RECUTTING
1.2.1.4 FLUSHING
TOO HIGH:
- UNNECESSARY ENERGY LOSS AT THE COMPRESSOR
- WATERFLUSHING WATER ENTERS INTO THE DRIFTER IF SEALING IS BROKEN
TOO LOW:
- LOW PENETRATION (INCREASED RECUTTING)
- EXCESSIVE BIT WEAR
- JAMMING
1.3 EXCAVATION COSTS VS. BIT COSTS
DRILL STRING ITSELF REPRESENTS JUST 7% OF THE TOTAL COST OF ROCK EXCAVATION. THE COST OF THE BITS IS AROUND HALF, BUT ITS SIGNIFICANCE FAR EXCEEDS THIS HOWEVER.
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