fluid_properties · water properties
Water Formation Volume Factor (Bw)
Bw = (1+ΔVwP)(1+ΔVwT) [McCain 1990]
click formula to derive ↑
Inputs
psi
°F
Description
Computes water formation volume factor (Bw) — the ratio of brine volume at reservoir conditions to its volume at stock-tank conditions — from McCain's (1990) thermal-expansion-times-pressure-compression correlation. Bw is required for water influx, water material balance, and produced-water volume conversions.
Variables
| Symbol | Unit | Description |
|---|---|---|
| Bw | RB/STB | Water FVF (Bw) |
| P | psi | Reservoir pressure at which Bw is evaluated. |
| T | °F | Reservoir temperature at which Bw is evaluated. |
Assumptions
- Formation water is a NaCl brine of moderate salinity — the correlation is not separately parameterized by salinity in this implementation
- Reservoir conditions are within or near McCain's fitted range (to 260°F, to 5,000 psia)
- No dissolved gas content beyond what is implicitly represented in the correlation's own calibration dataset
Limitations
- No cleaner single-paper primary source than the McCain (1990) textbook compilation was identified this session for this exact polynomial form — flagged per Phase 1's explicit instruction rather than silently citing only a secondary compilation without disclosure
- Does not take a salinity input directly — brines far from typical oilfield salinity may deviate from this fit
- McCain reports ~2% agreement with a limited published dataset — treat as a solid engineering estimate, not a lab-grade result
Use Cases
- → Water influx / aquifer material balance: Supply Bw to convert produced or influx water volumes between reservoir and stock-tank conditions in aquifer and water-drive material balance.
- → Waterflood volume accounting: Convert injected/produced water volumes at surface conditions to reservoir volumes for voidage-replacement ratio calculations.
- → Total system compressibility: Pair with water_compressibility when building the pressure-dependent water volume term in reservoir simulation input decks.
Related Calculations
Region Notes
Global
Bw is close to 1.0 RB/STB across almost all reservoir conditions (typically 1.00–1.04) since water is far less compressible and less gas-saturated than oil — a computed Bw far outside 0.99–1.06 usually signals an input error rather than an unusual fluid.
References
Primary source
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.