Changes

The distribution of shale and the salinity of formation water can significantly affect the resistivity of the formation. A variety of saturation models have been developed over the years to describe the influence of these factors. Some commonly used equations are as follows:

The distribution of shale and the salinity of formation water can significantly affect the resistivity of the formation. A variety of saturation models have been developed over the years to describe the influence of these factors. Some commonly used equations are as follows:

<disp-quote>Simandoux:

{{Quotation|Simandoux:

:<math>C_{\rm t} = \frac{C_{\rm w}}{F} S_{\rm w}^{2} + S_{\rm w}V_{\rm sh}C_{\rm sh}</math>

:<math>C_{\rm t} = \frac{C_{\rm w}}{F} S_{\rm w}^{2} + S_{\rm w}V_{\rm sh}C_{\rm sh}</math>

:<math>C_{\rm t} = \frac{C_{\rm w}}{F^{*}}S_{\rm W}^{n} + \frac{BQ_{\rm v}}{F^{*}} S_{\rm w}^{n-1}</math>

:<math>C_{\rm t} = \frac{C_{\rm w}}{F^{*}}S_{\rm W}^{n} + \frac{BQ_{\rm v}}{F^{*}} S_{\rm w}^{n-1}</math>

</disp-quote>For a more complete explanation of water saturation equations and their terms, refer to Worthington<ref name=pt04r22>Worthington, P., 1985, The evolution of shaly-sand concepts in reservoir evaluation: The Log Analyst.</ref> or Patchett and Herrick<ref name=pt04r9>Patchett, J. G., Herrick, D. C., 1982, A review of saturation models: SPWLA Reprint Volume Shaly Sands, SPWLA.</ref>. The Simandoux and Indonesia equations were designed mainly for relatively salty formation waters and moderate amounts of dispersed clay. The dual water and Waxman and Smits equations were designed for all water salinities and moderate amounts of dispersed clays.

For a more complete explanation of water saturation equations and their terms, refer to Worthington<ref name=pt04r22>Worthington, P., 1985, The evolution of shaly-sand concepts in reservoir evaluation: The Log Analyst.</ref> or Patchett and Herrick<ref name=pt04r9>Patchett, J. G., Herrick, D. C., 1982, A review of saturation models: SPWLA Reprint Volume Shaly Sands, SPWLA.</ref>. The Simandoux and Indonesia equations were designed mainly for relatively salty formation waters and moderate amounts of dispersed clay. The dual water and Waxman and Smits equations were designed for all water salinities and moderate amounts of dispersed clays.

Recommended logs to use for interpreting shaly sandstones are

Recommended logs to use for interpreting shaly sandstones are

* Dual laterolog or dual induction

* [[Dual laterolog]] or [[dual induction]]

* Density

* [[Density]]

* Compensated neutron

* [[Compensated neutron]]

* Spectral gamma ray

* [[Spectral gamma ray]]

===Carbonates and evaporites===

===Carbonates and evaporites===