drilling · cement
Top of Cement (TOC) Estimate
TOC = ShoeDepth − (Vpumped/Capacity)
click formula to derive ↑
Inputs
bbl
bbl/ft
ft
Description
Estimates the top of cement (TOC) in the annulus after a primary cement job by dividing the actual pumped volume by the annular capacity to get column height, then subtracting that height from the casing shoe depth. Used to verify cement coverage against the job design before relying on CBL or temperature log confirmation.
Variables
| Symbol | Unit | Description |
|---|---|---|
| TOC | ft | Top of Cement |
| V | bbl | Total cement slurry volume actually pumped into the annulus (excluding any left in the shoe track/casing). |
| Cap | bbl/ft | Annular capacity of the cemented interval, from the annular_capacity calculation. |
| Dshoe | ft | Measured depth of the casing shoe — the bottom reference point that the cement column height is measured up from. |
Assumptions
- Pumped volume figure excludes any cement left inside the casing (shoe track) below the float collar
- Annular capacity is reasonably uniform over the interval — significant washout will make the pre-job capacity estimate optimistic and TOC appear higher than actual
- No significant cement losses to the formation occurred during the job
Limitations
- This is a volumetric estimate only — actual TOC must be confirmed with a cement bond log (CBL), temperature log, or tracer survey before being relied upon for well integrity decisions
- Lost circulation during the job will make the actual TOC lower than this calculation predicts, since some pumped cement did not stay in the annulus
- Washout above gauge hole size will make the actual TOC lower than predicted, since more volume is needed to fill the same vertical interval
Use Cases
- → Post-job cement coverage verification: Cross-check the volumetric estimate of TOC against the cement job design before confirming with logging.
- → Remedial cementing planning: Identify likely TOC shortfall after a job with lost returns to plan a remedial (squeeze) cement job.
- → Regulatory compliance check: Provide a first-pass estimate of whether cement coverage meets state/regional minimum TOC requirements above a casing shoe or across a protected zone.
Related Calculations
Region Notes
Permian Basin
Regulatory requirements (Texas RRC, New Mexico OCD) typically require surface casing cement to reach surface and intermediate casing to cover usable-water zones — volumetric TOC estimates should always be confirmed against these specific depth requirements.
Global
A volumetric TOC estimate that disagrees significantly with a subsequent CBL or temperature survey usually points to lost circulation, washout, or a gas-cut cement column — investigate before proceeding with completion operations.
References
Need geoscience support? BauerCalc is just one of the tools we build. If you're looking for independent expertise in well planning, geosteering, reservoir characterization, or opportunity evaluation, visit BauerSubsurface.com.