geology · stratigraphic
Gross Rock Volume
GRV = Area × Gross Thickness
click formula to derive ↑
Inputs
acres
ft
Description
Computes gross rock volume — the total bulk rock volume enclosed by a mapped structural closure or stratigraphic interval — as the simple product of areal extent and gross thickness. This is the single-value 'box model' simplification of the full multi-contour planimetered volume a structure or isopach map would give, the same level of simplification already used by this platform's own ooip/giip volumetric calculators, and is the starting point of the standard reservoir volumetric equation chain (GRV -> Net Rock Volume -> Hydrocarbon Pore Volume -> OOIP/GIIP) before any petrophysical cutoffs or fluid properties are applied.
Variables
| Symbol | Unit | Description |
|---|---|---|
| GRV | acre-ft | Gross Rock Volume |
| A | acres | Areal extent of the structure or mapped closure — from a structure contour map, isopach map, or 3-D interpretation. 259 ha (≈640 acres / 1 section) is a common single-section reference size. |
| hg | ft | Gross (total) vertical thickness of the interval or structure being volumed — before any net-to-gross, porosity, or saturation cutoffs are applied. |
Assumptions
- Area and gross thickness are both representative single values for the structure or interval — a genuine multi-contour (pyramidal/trapezoidal-rule) volume integration across several structure or isopach contour levels would be more rigorous than this single-value box-model approximation, but is not reducible to a small set of scalar inputs.
- Area and gross thickness are measured on a consistent map/datum basis (the same structural closure or isopach interval).
- This calculator reports gross rock volume only — no porosity, saturation, or net-to-gross adjustment has been applied yet.
Limitations
- A single-value Area × Thickness box model, not a true multi-contour planimetered volume — for a structure with significant relief or a strongly variable thickness map, this will diverge from a properly integrated volume; treat it as a first-pass/quick-look estimate, the same caveat this platform's own ooip/giip calculators already carry for their own identical A×h simplification.
- The GRV = Area × Gross Thickness relationship is standard, widely-used reservoir-engineering content, corroborated across multiple secondary sources (general reservoir-engineering coursework and technical literature) — but no primary/textbook source was directly page-accessed this session for this specific formula (SEG Wiki's Volumetrics page and ScienceDirect's topic pages both returned 403 this session). Attributed to Dake's *Fundamentals of Reservoir Engineering* on the strength of it already being this platform's own cited source for the same A×h relationship inside ooip/giip, not because Dake's text was itself directly re-read this session — treat as attribution-corroborated, not page-checked, the same honest-disclosure standard already applied to formation_top_projection and the geochemistry/maturity batch.
- Does not itself account for net-to-gross, porosity, or saturation — see net_rock_volume for the next step in the chain.
Use Cases
- → Early-stage prospect sizing: Get a first-pass rock-volume estimate for a structural or stratigraphic closure as soon as area and gross thickness are mapped, before petrophysical cutoffs are available.
- → Feeding a volumetric workflow: Provide the starting bulk rock volume for a manual GRV -> NRV -> HCPV -> OOIP/GIIP volumetric chain, cross-checked against this platform's own ooip/giip calculators' internal A×h×φ×(1−Sw) math.
Related Calculations
Region Notes
Global
The single-value box-model approximation is most reliable for tabular, gently-dipping intervals of fairly uniform thickness — for structurally complex closures (steep-flanked domes, faulted panels with strongly variable thickness) a full multi-contour volume integration from dedicated mapping/GIS software will diverge materially from this simplified estimate.
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.