# Formation resistivity and porosity relations for carbonate rocks

## Input(s)

a: Constant (Range of 2.2 to 2.5 ) (dimensionless)

\(\Phi\): Porosity (dimensionless)

## Output(s)

\(F_{c}\): Formation Resistivity Factor for Chalky Rocks (dimensionless)

\(F_{c} O\): Formation Resistivity Factor for Compact Rocks (dimensionless)

\(F_{l}\): Formation Resistivity Factor for Low Porosity and non-fractured Carbonates, Shell Equation (dimensionless)

## Formula(s)

\[
\begin{gathered}
F_{c}=\frac{1}{(\Phi)^{2}} \\
F_{c} O=\frac{1}{(\Phi)^{a}} \\
F_{l}=\frac{1}{(\Phi)^{1.87+\left(\frac{0.019}{\Phi}\right)}}
\end{gathered}
\]

## Reference(s)

Bassiouni, Z., 1994, Theory, Measurement, and Interpretation of Well Logs. SPE Textbook Series Vol. 4. Chapter 1, Page: 10.