<p><strong>Short answer: it depends.</strong></p>

<p>The usual workflow is, very roughly, something like this:</p>

<ol>
<li>Condition all your data. Compute any 'missing' data you need or want (e.g. porosity $\phi$, lithofacies, saturation $S_\mathrm{W}$, S-wave velocity $V_\mathrm{S}$).</li>
<li>Inspect crossplots of relevant properties like velocity vs porosity, acoustic impedance vs elastic impedance (or maybe Poisson's ratio or ${V_\mathrm{P}}/{V_\mathrm{S}}$), and so on, colouring points by depth, $S_\mathrm{W}$ or lithofacies, say. Look for helpful discrimination. </li>
<li>Use judgment, research, advice, or inspiration to decide on how to use the relationships you find... perhaps you are aiming for seismic inversion, or facies prediction, or log modeling, or something else.</li>
</ol>

<p>Before doing much else, I recommend picking up Avseth et al. (Cambridge, 2005) (and/or perhaps  Dvorkin et al., Cambridge, 2014) and reading it from cover to cover. <a href="http://www.agilegeoscience.com/blog/2014/7/18/six-books-about-seismic-analysis.html" rel="nofollow noreferrer">Here are some short reviews and more details on these books.</a> Alessandro Amato's <a href="https://github.com/seg/tutorials" rel="nofollow noreferrer">two recent tutorials</a> in SEG's <em>Leading Edge</em> will help too, especially if you're using Python. If you're in MATLAB, a lot of the code for those books, which are both by the rock physics team at Stanford, <a href="https://pangea.stanford.edu/researchgroups/srb/resources/books/quantitative-seismic-interpretation" rel="nofollow noreferrer">is available online</a>.</p>

<p>Here are some nice $V_\mathrm{P}/V_\mathrm{S}$ <em>vs</em> acoustic impedance $I_\mathrm{P}$ crossplots from <a href="https://github.com/seg/tutorials/tree/master/1506_Seismic_petrophysics_2" rel="nofollow noreferrer">Amato's second tutorial</a> to inspire you:</p>

<p><a href="https://i.sstatic.net/YpGvh.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/YpGvh.png" alt="Vp/Vs vs P-wave impedance"></a></p>

CC BY-SA 3.0
2015-08-19T19:52:48.427Z
Taiwo: You're welcome. Feel free to select it as the answer if you found it useful. Up to you though!
Matt Hall
CC BY-SA 3.0
2015-08-17T15:23:16.930Z
2015-08-17T15:23:16.930Z
Matt Hall
<p>I recently developed a computer program that generates some petrophysical and elastic parameters from well logs such as water saturation and hydrocarbon saturation, bulk volume, irreducible water saturation, porosity, permeability, shear impedance, acoustic impedance, and poisson ratio. I would like to know which parameters to cross-plot. For example, can you use a cross-plot of depth versus acoustic impedance for detection of hydrocarbons? My analysis is aimed at reservoir characterization.  </p>

CC BY-SA 3.0
2015-08-15T20:31:53.230Z
Neutron-density is often useful, if you have access to that data. What do you mean by *generate*? Is it a synthetic model?
user2821
CC BY-SA 3.0
2015-08-18T09:21:26.950Z
thanks a lot for the help, Neutron-density cross-plot is for differentiating the phase of the hydrocarbon(i.e either oil and gas), and i meant compute(to calculate) instead of generate.
Taiwo
<geophysics>
petrophysical crossplots
Taiwo
# petrophysical crossplots

(Asked by: username_0 on 2015-08-15)

I recently developed a computer program that generates some petrophysical and elastic parameters from well logs such as water saturation and hydrocarbon saturation, bulk volume, irreducible water saturation, porosity, permeability, shear impedance, acoustic impedance, and poisson ratio. I would like to know which parameters to cross-plot. For example, can you use a cross-plot of depth versus acoustic impedance for detection of hydrocarbons? My analysis is aimed at reservoir characterization.

**Tags:** geophysics

> **Comments:**
> **username_1**: Neutron-density is often useful, if you have access to that data. What do you mean by *generate*? Is it a synthetic model?  
> **username_0**: thanks a lot for the help, Neutron-density cross-plot is for differentiating the phase of the hydrocarbon(i.e either oil and gas), and i meant compute(to calculate) instead of generate.  

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## 1 answers

### Answer by username_2 on 2015-08-17. Score: 7 | Accepted answer

**Short answer: it depends.**

The usual workflow is, very roughly, something like this:

1. Condition all your data. Compute any 'missing' data you need or want (e.g. porosity $\phi$, lithofacies, saturation $S\_\mathrm{W}$, S-wave velocity $V\_\mathrm{S}$).
2. Inspect crossplots of relevant properties like velocity vs porosity, acoustic impedance vs elastic impedance (or maybe Poisson's ratio or ${V\_\mathrm{P}}/{V\_\mathrm{S}}$), and so on, colouring points by depth, $S\_\mathrm{W}$ or lithofacies, say. Look for helpful discrimination.
3. Use judgment, research, advice, or inspiration to decide on how to use the relationships you find... perhaps you are aiming for seismic inversion, or facies prediction, or log modeling, or something else.

Before doing much else, I recommend picking up Avseth et al. (Cambridge, 2005) (and/or perhaps Dvorkin et al., Cambridge, 2014) and reading it from cover to cover. [Here are some short reviews and more details on these books.](http://www.agilegeoscience.com/blog/2014/7/18/six-books-about-seismic-analysis.html) Alessandro Amato's [two recent tutorials](https://github.com/seg/tutorials) in SEG's *Leading Edge* will help too, especially if you're using Python. If you're in MATLAB, a lot of the code for those books, which are both by the rock physics team at Stanford, [is available online](https://pangea.stanford.edu/researchgroups/srb/resources/books/quantitative-seismic-interpretation).

Here are some nice $V\_\mathrm{P}/V\_\mathrm{S}$ *vs* acoustic impedance $I\_\mathrm{P}$ crossplots from [Amato's second tutorial](https://github.com/seg/tutorials/tree/master/1506_Seismic_petrophysics_2) to inspire you:

[![Vp/Vs vs P-wave impedance](https://i.sstatic.net/YpGvh.png)](https://i.sstatic.net/YpGvh.png)

> **Comments:**
> **username_2**: username_0: You're welcome. Feel free to select it as the answer if you found it useful. Up to you though!  

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