Specialized Drilling Exam: Declared Method Command (Mud Rotary Example)
The specialized exam is one additional paper you choose - for example cable tool, mud rotary, or air rotary. It tests depth of command in that method: the rig and tooling, the circulating or lifting system, control of formation pressure, and the judgment calls when the hole misbehaves. The example below uses mud rotary, but the structure of the reasoning transfers to whatever specialty you declare.
What the specialty paper demands
- Mud does four jobs: cool the bit, carry cuttings, wall the hole with filter cake, and hold formation fluids back with hydrostatic pressure.
- Test and record density (mud balance), Marsh funnel viscosity, gel strength, filtrate, sand content, and pH at least once a tour and after every treatment.
- Annular velocity must beat the cuttings slip velocity; if cuttings load up, raise velocity before raising weight.
- Adding water drops density and viscosity; adding bentonite raises both. Weight up with barite only as far as the fracture gradient allows.
Worked example. What mud weight balances a 0.45 psi/ft formation at 600 ft, and what is the overbalance with 9.6 ppg mud? Formation pressure = 0.45 × 600 = 270 psi. Needed weight = 270 ÷ (0.052 × 600) = 8.65 ppg. With 9.6 ppg: 9.6 × 0.052 × 600 = 300 psi, an overbalance of about 30 psi. That margin keeps formation water out; it is also the pressure pushing filtrate into permeable sand, so if returns drop you are near the fracture gradient, not looking at a pump problem.
Traps
Reporting Marsh funnel seconds as viscosity. Comparing flowline mud weight with downhole conditions without correcting for temperature and entrained gas. Weighting up to cure a cuttings problem that is really an annular-velocity problem - the heavier mud often triggers lost circulation instead. Skipping the time log, which is the cheapest formation evaluation you will ever run.