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Simandoux Water Saturation from Shaly Sand Logs Calculator

Sw=−VshRsh+(VshRsh)2+4FRw(1−Vsh)Rt2FRw(1−Vsh)S_w=\frac{-\frac{V_{sh}}{R_{sh}}+\sqrt{\left(\frac{V_{sh}}{R_{sh}}\right)^2+\frac{4}{F R_w (1-V_{sh}) R_t}}}{\frac{2}{F R_w (1-V_{sh})}}

Enter the declared petrophysics inputs below to solve S_w. Variable definitions, units, the default calculation, and the available source trail are included on this page.

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Inputs

Defaults provide a quick field-unit example for the equation.

5 variables

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Extended guidance in preparation

What is available in this record

This record provides the functioning calculator, formula, declared variables and units, a reproducible default result, and the available citation metadata. A separately written engineering interpretation has not yet been published for this calculation.

Formula reference

Formula, variables, and default calculation

Sw=−VshRsh+(VshRsh)2+4FRw(1−Vsh)Rt2FRw(1−Vsh)S_w=\frac{-\frac{V_{sh}}{R_{sh}}+\sqrt{\left(\frac{V_{sh}}{R_{sh}}\right)^2+\frac{4}{F R_w (1-V_{sh}) R_t}}}{\frac{2}{F R_w (1-V_{sh})}}

Reproducible default result

With the default values shown below, the calculation returns S_w = 0.187156 fraction. Defaults demonstrate the implementation; they are not recommended field values.

Fdimensionless

25

R_wohm m

0.05

R_tohm m

20

V_shfraction

0.2

R_shohm m

2.5

Input definitions

F

dimensionless

Formation Resistivity Factor

R_w

ohm m

Formation Water Resistivity

R_t

ohm m

True Formation Resistivity

V_sh

fraction

Volume of Shale

R_sh

ohm m

Wet Shale Resistivity

Output definitions

S_w

fraction

Water Saturation

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.

reviewed

Standard interpretation, AAPG Wiki

AAPG Wiki. Standard Interpretation, Water saturation in shaly reservoirs; Simandoux equation.

Open source reference