Downhole · Abandonment
Cement Plug
A column of cement placed inside the casing or the open hole across a zone, a liner top or a casing shoe that must be isolated.
What it does
Seals the wellbore across the interval so fluids cannot move between zones or up the well. After placement its depth is confirmed by tagging and it is pressure tested.
Basics
| Open hole, under 1,500 m TVD | At least 30 m, from 15 m below to 15 m above the zone |
| Open hole, over 1,500 m TVD | At least 60 m |
| Liner top | 15 m below to 15 m above |
| Test | Tag, then 7,000 kPa for 10 minutes in casing |
| Oil sands | Thermal cement |
Common failures
- Cement contaminated with well fluid that never sets hard
Troubleshooting
- Symptom
- Plug top found lower than planned
- Likely cause
- Cement fell or was contaminated
- What to check
- Clean the hole, place a new plug and tag it again