Wood Fluid Bulk Modulus Calculator
Calculate Wood two-fluid mixture bulk modulus from water saturation and compatible fluid moduli in GPa. Review pressure-equilibration assumptions.
Calculate Wood two-fluid mixture bulk modulus from water saturation and compatible fluid moduli in GPa. Review pressure-equilibration assumptions.
Published by PetroCalcHub Team. Linked workflow tools and revision log.
Calculation context and source notes
Calculate the pressure-equilibrated bulk modulus of a two-fluid pore mixture using the saturation-weighted harmonic relation. The second fluid fraction is one minus water saturation, so the two pore-volume fractions close exactly by construction.
Supply water or brine modulus and the other fluid modulus at the same reservoir conditions, then evaluate their effective mixture modulus for a rock-physics calculation. Both moduli are entered in GPa and the water fraction is entered as a fraction.
Solves for
K_f (GPa)
Best next page
Formula, variables, and sourceWhy the softer fluid dominates
At water fraction 0.70, K_w = 2.2 GPa and K_h = 0.1 GPa, the compliance sum is 0.7/2.2 + 0.3/0.1 = 3.3181818 per GPa. Its reciprocal is 0.301370 GPa. The arithmetic average would be 1.57 GPa and would not evaluate this relation.
At water fraction zero the result is 0.1 GPa, and at water fraction one it is 2.2 GPa. If both phase moduli are equal, the mixture returns that same modulus at any fraction. For positive moduli the harmonic result remains between the two phase moduli.
| Water fraction | Mixture modulus (GPa) |
|---|---|
| 0 | 0.1 |
| 0.70 | 0.301370 |
| 1 | 2.2 |
Transfer fluid properties on one basis
Bulk modulus and compressibility are reciprocals only when they refer to the same thermodynamic process and units. A gas isothermal compressibility coefficient is not automatically the adiabatic fluid modulus needed for a seismic-frequency application. Establish the appropriate process before transferring PVT properties.
Feed the effective modulus into Gassmann only after considering saturation distribution and equilibration. The numerical example uses illustrative phase moduli; it is not a brine or gas PVT correlation and does not establish how those phase properties change with reservoir pressure or temperature.
Formula, variables, and default calculation
Reproducible default result
With the default values shown below, the calculation returns K_f = 0.30137 GPa. Defaults demonstrate the implementation; they are not recommended field values.
0.7
2.2
0.1
Input definitions
S_w
fractionWater Fraction of Pore-Fluid Volume
K_w
GPaWater or Brine Bulk Modulus at the Selected Conditions
K_h
GPaOther Fluid Bulk Modulus at the Same Conditions
Output definitions
K_f
Pressure-Equilibrated Fluid Mixture Bulk Modulus
Engineering use, assumptions, and limits
Supply water or brine modulus and the other fluid modulus at the same reservoir conditions, then evaluate their effective mixture modulus for a rock-physics calculation. Both moduli are entered in GPa and the water fraction is entered as a fraction.
Assumptions
- Two fluid fractions account for the entire pore-fluid volume at the selected conditions.
- Pore-fluid pressures equilibrate on the relevant timescale, making the harmonic mixing basis appropriate.
Limitations
- Does not predict phase PVT properties, density, sound speed or saturated rock modulus.
- A pressure-equilibrated mixture is not a general model of patchy saturation or disconnected fluid pockets.
Common mistakes
- Using an arithmetic modulus average in place of the saturation-weighted compliance average.
- Entering water saturation as percent without converting it, or using fluid moduli from different conditions.
Frequently asked questions
What inputs does the Wood Two-Phase Fluid Bulk Modulus calculator need?
The calculation uses Water Fraction of Pore-Fluid Volume (S_w), Water or Brine Bulk Modulus at the Selected Conditions (K_w), Other Fluid Bulk Modulus at the Same Conditions (K_h). Enter values on the units shown beside each field.
What result does this calculator return?
The primary result is pressure-equilibrated fluid mixture bulk modulus in GPa. The formula section shows the declared relationship, variables, and a reproducible default calculation.
What should I check before using the result?
Confirm the unit basis, source applicability, and input quality. Does not predict phase PVT properties, density, sound speed or saturated rock modulus. Using an arithmetic modulus average in place of the saturation-weighted compliance average.
Source and record status
Source metadata identifies the relationship implemented by the calculator. Check the cited edition, unit basis, and scope against the engineering case before operational use.
Construction of 2D and 3D rock physics templates for quantitative prediction of physical properties of a carbonate reservoir in SW of Iran, Forouzan Rahmani, Mohammad Emami Niri, Golnaz Jozanikohan (2023)
Rahmani, Emami Niri and Jozanikohan (2023), Journal of Petroleum Exploration and Production Technology 13, 449-470, equation 15; two-fluid specialization with S_h = 1 - S_w.
Open source reference