In backfilling the annulus, which of the following is NOT a primary purpose?

• A. Sealing around the screen
• B. Providing mechanical support to casing
• C. Preventing contaminant migration between formations
• D. Enhancing gas venting through the grout

Answer: (D)

Backfilling the annulus is about creating a hydraulic and structural barrier around the well to protect the aquifer and keep the casing stable. The grout around the screen seals the annulus so that water and potential contaminants must pass through the grout or through the designed well completions rather than bypassing the screen, which helps prevent short-circuiting between formations. It also fills the space to provide mechanical support to the casing, helping to keep the casing centered and resisting movement or collapse. By forming a low-permeability barrier between formations, the grout prevents contaminant migration from one formation to another or into the borehole.

Enhancing gas venting through the grout is not a primary purpose. Grout is intended to seal and isolate, not serve as a vent path. Gas venting, when needed, is addressed through appropriate venting systems or dedicated pathways, not the grout itself.