---
id: po.wb.pp.log-display
title: Well-Log Display — Chart Tracks over a Depth Grid, Paste-In Curves
category: Petrophysics
requires: []
tags:
  - well-log
  - log-display
  - log-tracks
  - petrophysics
  - gamma-ray
  - spontaneous-potential
  - resistivity
  - shale-volume
  - lithology
  - chart-tracks
---

# Well-Log Display — Chart Tracks over a Depth Grid, Paste-In Curves

## Description

A log display for one vertical well. Paste SP, gamma-ray and shallow, medium and deep resistivity onto the
Log Data sheet — any sampling interval, depth increasing downward — and the Well Log sheet draws them as
tracks against depth: SP as bars either side of a shale baseline, GR as bars coloured by a five-band
palette, a lithology column from the same palette, resistivity on a logarithmic scale with decade lines,
and a computed shale-volume track from the gamma-ray index. The tracks are charts over a grid of cells that
supplies the depth lines and labels, and the sheet prints on one page. No add-in is needed.

A window sets what the 120 track rows show: a top depth (0 means the top of the data) and the feet each row
covers. Each row reads the curves at its middle depth by linear interpolation, so the sampling of the log and
the scale of the display are independent. A sample that is blank, text or an error, equals the null value
(LAS files use −999.25) or, for resistivity, is not above zero, is a gap in that curve.

A chart's axis limits are numbers inside the chart, not cells, so a chart cannot follow a scale typed in a
cell. Here every track plots a share of its width — (GR − left edge) / (right edge − left edge), and for
resistivity the same in log space — computed on the Calc sheet from the scale cells, and the chart axis is
fixed at 0 to 1. Change a scale, the shale baseline, a palette edge or the window and the curves, the decade
lines and the scale printed under each track title all move.

Input checks flag a set of inputs that cannot draw a log — depths that run upward or repeat, text among the
depths, a window that misses the data, a scale whose left edge is above its right, more than six decades of
resistivity — in red with the fix spelled out.

## Inputs

Named cells you can edit — the curves, grid lines and headers recalculate from them. The curves themselves
are pasted on the Log Data sheet.

| Name | Description | Default | Unit |
|---|---|---|---|
| `LD_WellName` | Well name shown in the title | Example well A-12 | — |
| `LD_WinTop` | Window top (0 = top of the data) | 0 | ft |
| `LD_Step` | Depth per row; the log is 120 rows tall | 1 | ft |
| `LD_Null` | Null value: a sample equal to it is a gap | −999.25 | — |
| `LD_SPBase` | SP shale baseline | −15 | mV |
| `LD_SPMin`, `LD_SPMax` | SP scale, left and right edge | −100, 0 | mV |
| `LD_GRMin`, `LD_GRMax` | GR scale, left and right edge | 0, 150 | API |
| `LD_RMin`, `LD_RMax` | Resistivity scale, left and right edge (log, at most six decades) | 0.2, 2000 | ohm·m |
| `LD_GRB1`–`LD_GRB4` | GR palette edges: clean sand, sand, shaly sand, sandy shale, shale | 45, 65, 85, 105 | API |
| `LD_GRClean`, `LD_GRShale` | GR in clean sand (Vsh = 0) and in shale (Vsh = 1) | 30, 115 | API |

## Sheets

- `Guide`
- `Inputs`
- `Log Data`
- `Well Log`
- `Calc`

The Well Log sheet carries four chart tracks — SP, GR, resistivity and Vsh — over a depth grid of cells and a
lithology column of patterned cells. The curves are on Log Data, columns A–F, rows 5–5004.

## Functions used

None — plain Excel formulas only.