Drilling Methods, Equipment, and Operations
Drilling Methods, Equipment, and Operations
This domain tests method selection and real-time operations: rotary air, mud rotary, cable tool, hollow-stem auger, and reverse circulation. In New York’s glacial deposits, auger and mud rotary are common for unconsolidated material; air rotary and down-the-hole hammer are common in bedrock. Cable tool is slower but useful where samples are needed and water loss is a concern. The exam expects you to connect geology, hole stability, cuttings transport, and water quality.
Core rules
- Mud rotary: mud cools the bit, stabilizes the hole, and lifts cuttings. Monitor viscosity, weight, sand content, and lost circulation.
- Air rotary: fast in hard rock but can plug fractures with fines and can spread contamination; use a foam or water mist when dust is excessive.
- Augers: good for shallow unconsolidated holes; do not use where contamination could migrate down the flights.
- Cable tool: fracture-driven; keep tools and casing aligned; bail cuttings regularly.
Worked example
A 4.5-in borehole with 2.875-in drill pipe is pumped at 150 gpm. Annular area = π/4 × (4.5² − 2.875²) = 10.4 in² = 0.072 ft². Convert flow: 150 gpm ÷ 7.48 = 20.1 ft³/min. Annular velocity = 20.1 ÷ 0.072 ≈ 279 ft/min. That is generally adequate to lift cuttings, but if cuttings settle or the hole packs off, increase flow, adjust mud properties, or reduce penetration rate. The reasoning is annular velocity, not pump pressure alone.
Traps
- Confusing pump pressure with cuttings-carrying capacity; annular velocity is the controlling variable.
- Using air rotary through contaminated soil and spreading contaminants.
- Letting mud weight climb until the formation fractures and circulation is lost.
- Failing to record drilling-fluid losses, which can indicate a fracture or a contaminated zone.