PetrophysicsResistivity Logs

Indonesian Water Saturation from Shaly Sand Logs Formula

S_w=\left[\frac{\sqrt{1/R_t}}{\frac{V_{sh}^{1-0.5V_{sh}}}{\sqrt{R_{sh}}}+\sqrt{\frac{\phi_e^m}{aR_w}}}\right]^{2/n}

Indonesian Water Saturation from Shaly Sand Logs calculates water saturation for resistivity logs workflows in petrophysics.

Calculate

How engineers use this formula

Use this formula when the listed inputs (R_t, V_sh, R_sh, phi_e, m, a, R_w, n) are known and the assumptions behind the cited resistivity logs relationship match the engineering case being checked.

Assumptions

Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
The declared units match the field-unit constants used in the formula.
The cited formula applies to the selected petroleum engineering workflow.

Limitations

The calculation does not replace a full engineering model or operating procedure.
Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.

Common mistakes

Mixing unit systems without converting the inputs.
Using default example values as field recommendations.
Applying the formula outside the source assumptions.

Default example

Using the default inputs, S_w equals 0.214387 fraction.

R_tohm m

V_shfraction

0.2

R_shohm m

2.5

phi_efraction

0.2

mdimensionless

adimensionless

R_wohm m

0.05

ndimensionless

Inputs

R_t

ohm m

True Formation Resistivity

V_sh

fraction

Volume of Shale

R_sh

ohm m

Wet Shale Resistivity

phi_e

fraction

Effective Porosity

m

dimensionless

Cementation Exponent

a

dimensionless

Tortuosity Factor

R_w

ohm m

Formation Water Resistivity

n

dimensionless

Saturation Exponent

Outputs

S_w

fraction

Water Saturation

Source and review

reviewed

Evaluation of Water Saturation in Shaly Formations, Poupon, A., Leveaux, J. (1971)

Poupon, A. and Leveaux, J. 1971. Evaluation of Water Saturation in Shaly Formations. SPWLA 12th Annual Logging Symposium; Nafta Wiki formula entry for Indonesia Model.

Source