Grouting, Sealing, and Annular Space Integrity
Grouting, Sealing, and Annular Space Integrity
This domain tests the seal that separates a well from the surface and from other aquifers. Items are usually about material and method: what goes in, how it is placed, and whether enough was used.
Purpose and standard
- The annular seal stops surface water, shallow contaminated groundwater, and poor-quality water from moving down the outside of the casing, and stops artesian cross-flow between zones.
- Acceptable materials include neat cement (Portland cement and water), cement-bentonite, sand-cement, and high-solids bentonite grout mixed at a low water-to-solids ratio or polymer-modified. Bentonite chips or pellets are used only where the rule allows, and never as a substitute for a continuous grout column in a critical seal.
- Placement is by tremie - a grout pipe run to the bottom of the interval - using a positive-displacement pump, grouting bottom-up in one continuous operation. Never pour grout from the surface.
Volume and job control
- Annular volume = π/4 × (hole diameter² − casing outside diameter²) × length. Add 25–50 percent excess, more where the hole is washed out, fractured, or in karst.
- Neat cement yields roughly 1.1–1.2 ft³ per 94-lb sack.
- Grout promptly after drilling; if the hole has caved or bridged, ream and clean first. Support the casing until the grout sets.
Worked example
A 10-inch hole with 6-inch casing (OD 6.625 in) grouted from 0 to 60 ft. Annular area = π/4 × (10² − 6.625²) = π/4 × (100 − 43.9) = 44.0 in² = 0.306 ft². Volume = 0.306 × 60 = 18.4 ft³. With 50 percent excess = 27.6 ft³. At 1.18 ft³ per sack, that is about 23–24 sacks. The inspector checks both the material ticket and the placement method, so record sacks used and tremie depth.
Traps
- Dumping bentonite or cement from the top and trusting gravity.
- Underestimating volume and leaving the top of the annulus unsealed.
- Using drilling mud or cuttings as the "seal."
- Grouting casing that was not centralized, producing a thin seal on one side.