<p><strong>It's a mistake.</strong></p>

<p>You probably know this, but for anyone who's interested, these wireline logs are:</p>

<ul>
<li><strong>DRHO</strong> — <a href="https://www.spec2000.net/07-densitylog.htm">density</a> ('RHO') correction (delta, or 'D') in g/cc.</li>
<li><strong>DPHI</strong> — porosity ('PHI') from <a href="https://www.spec2000.net/07-densitylog.htm">density</a> ('D'), as a fractional proportion.</li>
<li><strong>NPHI</strong> — porosity from <a href="https://www.spec2000.net/07-neutronlog.htm">the neutron log</a> ('N'), as a fractional proportion.</li>
</ul>

<p>All of these logs are usually displayed on a linear scale. Indeed it wouldn't make sense to display them on a log scale, which is mainly for displaying resistivity logs, e.g. <a href="https://www.spec2000.net/07-indlog.htm">the induction log</a>. Even if they were, it wouldn't make sense to show the usual 4 octaves (0.2 to 2000 for resistivity), given the range of the data and the scale of porosity values geologists are interested in.</p>

<p>It's not clear if the data have actually been displayed on a log scale, or if it's just that the grid has been erroneously added. I would treat the data with suspicion.</p>

CC BY-SA 3.0
2016-04-13T18:26:16.590Z
2016-04-13T18:26:16.590Z
Matt Hall
<p>Why is there a logarithmic grid when these <a href="https://en.wikipedia.org/wiki/Well_logging" rel="noreferrer">wireline density and neutron porosity logs</a> have linear scale labels, and when these logs are usually displayed on linear scales?</p>

<p><a href="https://i.sstatic.net/fmnfY.jpg" rel="noreferrer"><img src="https://i.sstatic.net/fmnfY.jpg" alt="Part of wireline log printout"></a></p>

CC BY-SA 3.0
2016-04-12T09:48:24.497Z
What is your question?
Pont
CC BY-SA 3.0
2016-04-12T13:45:35.000Z
Reading between the lines (ha), I think the question is, "Why is there a logarithmic grid when the logs have linear scale labels, and when these logs are usually displayed on linear scales?". It's a fair question. I think it's a mistake, and it would make me question the quality of the data.
Matt Hall
CC BY-SA 3.0
2016-04-13T08:28:12.367Z
Could you give some information on the origin of the data and what is displayed?
daniel.heydebreck
CC BY-SA 3.0
2016-04-13T08:42:44.173Z
@kwinkunks Judging by the latest edit, your guess was extremely accurate! :)
Pont
CC BY-SA 3.0
2016-04-13T13:23:02.450Z
Maybe it helps if you tell us what we actually see in this picture, so that we know how the quantities involved scale...
Jan Doggen
<data-formats><visualization>
Why is there a logarithmic grid on this plot?
Khaled El-kilany
# Why is there a logarithmic grid on this plot?

(Asked by: username_0 on 2016-04-12)

Why is there a logarithmic grid when these [wireline density and neutron porosity logs](https://en.wikipedia.org/wiki/Well_logging) have linear scale labels, and when these logs are usually displayed on linear scales?

[![Part of wireline log printout](https://i.sstatic.net/fmnfY.jpg)](https://i.sstatic.net/fmnfY.jpg)

**Tags:** data-formats, visualization

> **Comments:**
> **username_1**: What is your question?  
> **username_2**: Reading between the lines (ha), I think the question is, "Why is there a logarithmic grid when the logs have linear scale labels, and when these logs are usually displayed on linear scales?". It's a fair question. I think it's a mistake, and it would make me question the quality of the data.  
> **username_3**: Could you give some information on the origin of the data and what is displayed?  
> **username_1**: @kwinkunks Judging by the latest edit, your guess was extremely accurate! :)  
> **username_4**: Maybe it helps if you tell us what we actually see in this picture, so that we know how the quantities involved scale...  

---

## 1 answers

### Answer by username_2 on 2016-04-13. Score: 5

**It's a mistake.**

You probably know this, but for anyone who's interested, these wireline logs are:

* **DRHO** — [density](https://www.spec2000.net/07-densitylog.htm) ('RHO') correction (delta, or 'D') in g/cc.
* **DPHI** — porosity ('PHI') from [density](https://www.spec2000.net/07-densitylog.htm) ('D'), as a fractional proportion.
* **NPHI** — porosity from [the neutron log](https://www.spec2000.net/07-neutronlog.htm) ('N'), as a fractional proportion.

All of these logs are usually displayed on a linear scale. Indeed it wouldn't make sense to display them on a log scale, which is mainly for displaying resistivity logs, e.g. [the induction log](https://www.spec2000.net/07-indlog.htm). Even if they were, it wouldn't make sense to show the usual 4 octaves (0.2 to 2000 for resistivity), given the range of the data and the scale of porosity values geologists are interested in.

It's not clear if the data have actually been displayed on a log scale, or if it's just that the grid has been erroneously added. I would treat the data with suspicion.


---

