A gravel pack has one job: hold back the formation while letting water through at the design yield. Too coarse and sand passes into the well. Too fine and the pack itself blinds, the specific capacity drops, and the pump works against a restriction that was built in on day one.
The calculation
Take a formation sample and run a sieve analysis. Find D₅₀ — the size at which half the formation passes. The pack is then sized at roughly four to six times that figure, with the lower multiplier for uniform formations and the higher for well-graded ones. The screen slot size follows from the pack, not the other way round.
- Pack material should be rounded, high-silica and washed free of fines — angular material bridges and blinds.
- Acid solubility matters here too: a pack that dissolves opens paths for sand.
- Send us the formation sieve analysis and we will calculate the pack — it is a free service and it takes a day.