Flowing Annulus on a Fractured-Rock Domestic Well
A driller completes a 6-inch PVC-cased domestic well to 340 ft in fractured crystalline rock. At 215 ft the bit enters a water-bearing fracture, and the water level rises to 8 ft below land surface. After the casing is set and the annulus is sealed with bentonite grout, water begins flowing from the annulus at an estimated 4 gpm. The casing currently extends 24 inches above grade. The homeowner wants it cut to 12 inches so a retaining wall can be built. The driller's assistant suggests pulling the casing up 10 ft to improve the seal and adding a grout cap. The driller has not submitted the well log. State rules require the casing to extend at least 12 inches above grade and the annular space to be sealed to land surface. The well permit allows a maximum yield of 15 gpm and does not authorize a flowing well.
1. Can the driller cut the casing to 12 inches and consider the well complete? Explain the construction and reporting issues.
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Cutting to 12 inches is not automatically acceptable, and the well is not complete while the annulus flows. The 12-inch figure is a minimum casing height, not a license to cut into a compromised seal. Flow outside the casing suggests the bentonite seal did not isolate the fracture or that the grout bridged. Cutting the casing could reduce the seal, and pulling it up 10 ft would likely break the annular seal and create a larger void. A grout cap alone does not fix a flowing annulus. Before cutting, the driller should notify the State Engineer's office, document static and flowing levels, and get approval if a variance is needed. The well log must be submitted with accurate construction details. If the flow cannot be stopped, the well may need a flow-control seal or be plugged and abandoned.
2. What should the driller do about the 4 gpm annular flow, and what tests or records should accompany the fix?
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Treat the 4 gpm as a seal failure until proven otherwise. Isolate the annulus with a packer and measure flow and pressure; determine whether water is coming up outside the casing or through the casing. If outside, ream or clean the annulus as practical and pressure-grout with neat cement or high-solids bentonite from the bottom up, using a tremie. Do not just dump chips from the top. Record grout mix, volume, pressure, and returns. If the fracture is artesian, a grout plug may be pushed out; in that case use a packer or stage grouting and possibly a well seal at the top. After grouting, wait for set, then verify the annulus is sealed and the casing is stable. Submit a complete well log and a narrative of the repair to the State Engineer, and advise the owner not to cut the casing until the seal is verified.