Drilling Well Control
Drilling Well Control
This domain tests the basic pressure-control model used while drilling: what keeps formation fluids in the formation, how a kick is recognised and shut in, and how surface shut-in pressures are converted into mud weight. Level 2 questions emphasise correct units, true vertical depth, and the difference between a measured surface pressure and the actual formation pressure.
Core rules and concepts
- Primary control is hydrostatic pressure from the mud column. In field units, HP (psi) = 0.052 × mud weight (ppg) × TVD (ft). Use TVD, not measured depth.
- Formation pressure is pore pressure. Overbalance exists when hydrostatic pressure exceeds formation pressure; underbalance allows an influx.
- Kick indicators include flow with pumps off, pit gain, increasing return flow, and changing pump pressure. Shut in promptly and record SIDPP and SICP.
- SIDPP is the pressure needed to balance formation pressure after subtracting the hydrostatic pressure of the existing mud. SICP is usually higher because it also reflects the influx and U-tube effect.
- Kill mud weight = current mud weight + SIDPP / (0.052 × TVD).
Worked example
TVD is 10,000 ft, mud weight is 10.0 ppg, and SIDPP is 400 psi. Hydrostatic pressure = 0.052 × 10.0 × 10,000 = 5,200 psi. Formation pressure = 5,200 + 400 = 5,600 psi. Equivalent mud weight = 5,600 / (0.052 × 10,000) = 10.77 ppg. A kill mud of about 10.8 ppg balances the zone before any planned overbalance margin is added.
Traps that cost marks
Using measured depth instead of TVD; treating SIDPP as formation pressure; mixing ppg with psi/ft gradients; assuming SICP should equal SIDPP; and failing to shut in before pressures stabilise.