Drilling Engineering
Drilling Engineering tests wellbore pressure management, casing and cement design, mud hydraulics, directional drilling, and well-control response. The exam favors calculations using true vertical depth, mud weight, and pressure gradients.
Core rules
- Hydrostatic pressure in psi = 0.052 × MW(ppg) × TVD(ft). The pressure gradient in psi/ft is 0.052 × ppg.
- Pore pressure and fracture gradient define the mud-weight window. Keep hydrostatic pressure between them with trip and kick margins.
- On a kick, shut in and record SIDPP and SICP. Kill weight MW = original MW + SIDPP/(0.052 × TVD).
- Casing seats are chosen by pressure and isolation needs, not depth alone. Cement provides zonal isolation and shoe support.
- Equivalent circulating density includes annular friction; surge and swab occur during trips.
Worked example
At TVD 8,000 ft and MW 12.0 ppg, hydrostatic pressure is 12 × 0.052 × 8,000 = 4,992 psi. If pore pressure is 4,500 psi, overbalance is 492 psi. A fracture gradient of 0.70 psi/ft gives fracture pressure 5,600 psi. Maximum static mud weight is 5,600/(0.052 × 8,000) = 13.46 ppg. If SIDPP is 300 psi, kill weight is 12.0 + 300/(0.052 × 8,000) = 12.72 ppg. Convert all values to pressure at the same TVD before comparing.
Traps
Using measured depth instead of TVD in deviated wells is a common error. Do not confuse psi/ft with ppg or omit the 0.052 factor. A mud that is safe statically may fracture the formation while circulating because of ECD, surge, or swab. Ignoring kick tolerance can make a casing seat look acceptable when it is not.
Key points
- Hydrostatic psi = 0.052 × ppg × TVD.
- Mud-weight window lies between pore and fracture pressures.
- Kill weight uses SIDPP and TVD, not measured depth.
- ECD adds annular friction to static mud pressure.
- Kick tolerance is a design constraint, not just a drilling check.