petrophysics · water saturation
Bulk Volume Water (BVW)
BVW = φ × Sw
click formula to derive ↑
Inputs
fraction
fraction
Description
Computes the bulk volume of water — the fraction of total rock volume occupied by water — as the simple product of porosity and water saturation. A near-constant BVW across an interval is the classic Pickett plot signature of a zone at irreducible water saturation.
Variables
| Symbol | Unit | Description |
|---|---|---|
| BVW | fraction | Bulk Volume Water |
| φ | fraction | Effective or total porosity at the depth of interest — use the same porosity curve used for the Sw calculation. |
| Sw | fraction | Water saturation from Archie or another Sw model at the same depth as the porosity value. |
Assumptions
- Porosity and Sw used together come from the same depth and are internally consistent (same porosity definition)
- Formation is at or near irreducible water saturation for the Pickett-plot interpretation to apply
- Rock type (grain size, sorting) is reasonably uniform across the interval being compared
Limitations
- A constant BVW does not guarantee water-free production — it indicates Swirr, but mobile water can still exist in heterogeneous or fractured rocks
- The 0.065 cutoff is a sandstone rule of thumb and shifts significantly for carbonates or fine-grained rocks
- Errors in either φ or Sw propagate directly and multiplicatively into BVW
Use Cases
- → Water-free production prediction: Flag intervals with BVW below a local cutoff as likely to produce without significant water cut.
- → Pickett plot analysis: Overlay constant-BVW hyperbolas on a porosity-vs-resistivity Pickett plot to visually identify the irreducible water saturation trend and pick a/m/n.
- → Pay flag QC: Use BVW consistency as a quality check on Sw and porosity calculations — erratic BVW across a uniform lithology suggests a log or parameter problem.
Related Calculations
Region Notes
Permian Basin
Wolfcamp tight sands/carbonates: BVW values of 0.03-0.06 are common at Swirr; values above ~0.08 typically indicate a transition or wet zone.
Gulf of Mexico
Higher-porosity unconsolidated sands can have BVW at Swirr in the 0.08-0.12 range — the 0.065 sandstone rule of thumb should be re-calibrated locally.
Global
Build a Pickett plot for each new field/formation before relying on a BVW cutoff — the irreducible BVW value is rock-type specific and should be read off the data, not assumed.
References
Primary source
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