Well Construction and Drilling Methods
What the exam tests
This domain covers how a North Carolina well is actually built: drilling-method selection, casing and screen design, the annular seal, wellhead completion, and development. Expect questions that ask you to sequence construction and to catch a design that cannot meet NC minimums.
Core rules
- A well construction permit must be issued by the local health department before drilling begins.
- Casing must be new material and must extend at least 20 feet below land surface; grout fills the annulus from the bottom of the casing to grade.
- The wellhead casing must terminate at least 12 inches above finished grade, with the ground sloped away.
- Rotary air, mud rotary, cable tool, and auger each have a place: unconsolidated sand often needs mud or a driven screen; fractured bedrock is commonly air-percussion.
- Development - surging, bailing, air-lifting, or fracturing - removes drilling fines and stabilizes the filter pack before the pump test.
Worked example
An 8-inch borehole is drilled to 40 ft and fitted with 6-inch steel casing. You must grout the annulus to surface. Annular area = π/4 × (8² − 6²) = 28 in² = 0.194 ft². Volume = 0.194 × 40 = 7.8 ft³. At about 1.15 ft³ of neat-cement slurry per 94-lb sack, that is 6.8 sacks; add 10% for loss, so order 8 sacks. The reasoning: compute the actual annular volume, convert units before multiplying, then add a loss allowance.
Traps
Using the borehole volume instead of the annulus; forgetting the 20-ft minimum; grouting from the top and bridging the annulus; and completing the wellhead at grade, which invites surface water into the casing.