drilling · cement
Cement Slurry Volume & Sacks Required
V = Capacity × L × (1+excess); Sacks = V/Yield
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Inputs
bbl/ft
ft
fraction
ft³/sack
Description
Computes the total cement slurry volume and the number of sacks of cement required for a primary cementing job, given the annular capacity, interval length, an excess factor for hole washout, and the slurry yield at the design water ratio.
Variables
| Symbol | Unit | Description |
|---|---|---|
| V | bbl | Slurry Volume Required |
| N | sacks | Sacks Required |
| Cap | bbl/ft | Annular capacity of the interval being cemented, from the annular_capacity calculation. |
| L | ft | Length of annulus to be filled with cement, from the planned top of cement to the shoe. |
| ex | fraction | Fractional excess volume pumped beyond gauge-hole capacity to compensate for washout and hole irregularity — 0.3 means 30% excess. |
| Yield | ft³/sack | Mixed slurry volume produced per sack of cement at the design water ratio (0.0398 m³/sack ≈ 1.40 ft³/sack, typical for Class H cement at normal water ratio). |
Assumptions
- Annular capacity input already reflects the correct interval geometry (use annular_capacity for a gauge-hole estimate, or caliper-log-derived capacity if available)
- A single uniform slurry design (one yield value) is used across the entire interval — a two-stage job (lead/tail slurry) requires this calculation run separately for each stage
- Excess factor is appropriate for the formation — soft/unconsolidated or naturally fractured intervals require higher excess than competent, gauge-drilling formations
Limitations
- Does not account for the inside-casing volume (shoe track) below the float collar, which must be added separately if not already included in L
- Does not model lost circulation during the cement job, which can require additional cement beyond this calculated volume
- Caliper-log-based excess estimation is always more reliable than an assumed excess factor where available
Use Cases
- → Primary cement job design: Determine the cement volume and sack count to order and mix for a casing or liner cementing job before pumping.
- → Lead/tail slurry staging: Run separately for the lead and tail slurry intervals of a two-stage cement design to get sack counts for each stage.
- → Cost estimation: Provide the sack count needed for cementing cost estimates during well planning and AFE preparation.
Related Calculations
Region Notes
Permian Basin
Surface casing cement jobs in unconsolidated near-surface formations commonly use 50-100% excess due to washout, while deeper intermediate/production strings in competent Permian carbonates/shales often use 20-35% excess.
Global
Class G and Class H cements (API designations) are the most common base cements for oilwell primary cementing, with slurry yield varying roughly 0.037-0.045 m³/sack (1.30-1.60 ft³/sack) depending on water ratio and additives.
References
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