# One well. Nine layers.

A reproducible synthetic LAS from 500 to 1,500 m: shale, gas, oil, a tight cemented layer and brine.

Danila Karnaukh | v4 | 2026-09-29

**Entirely fictional data.** 4,001 samples at 0.25 m spacing; 14 curves; LAS 2.0. The known FACIES labels describe the model, not an automated interpretation.

[Run four-track display →](../../logs/index.html?example=four-track)[Density–neutron](../../crossplot/index.html?example=density-neutron)[Density–sonic](../../crossplot/index.html?example=density-sonic)[Cement detail](../../logs/index.html?example=cement-detail)

## Download and reproduce

[Download the LAS file](Petrophysics_SYNTH_500-1500m.las) · [Model generator (Python; NumPy + SciPy)](generate_synthetic_las.py) · [Model QC summary](qc_summary.json)

Settings: [four tracks](four-track.scene.json) · [density–neutron](density-neutron.scene.json) · [density–sonic](density-sonic.scene.json) · [cement detail](cement-detail.scene.json). Load the LAS first, then Load settings in the matching tool.

## The geological sequence

| Depth, m | Assigned layer | FACIES |
| --- | --- | --- |
| 500–620 | Shale | 1 |
| 620–800 | Gas sandstone | 2 |
| 800–820 | Thin shale | 1 |
| 820–960 | Oil sandstone | 3 |
| 960–968 | Tight calcite-cemented sandstone; water-filled | 4 |
| 968–1110 | Oil sandstone | 3 |
| 1110–1210 | Shale | 1 |
| 1210–1410 | Brine sandstone | 5 |
| 1410–1500 | Shale | 1 |

Boundary samples belong to the deeper layer; the final sample at 1,500 m is included. Tool responses are smoothed across boundaries.

## Model choices

The generator uses seed 20260929, correlated variations and vertical smoothing. Bulk density mixes quartz/calcite, pore fluid and shale components. Assigned densities are quartz 2.65, calcite 2.71, brine 1.025, oil 0.80 and gas 0.12 g/cm³. These are demonstration inputs, not PVT estimates for the chosen depths.

NPHI uses sandstone units with an illustrative fluid/hydrogen-index response and partial invasion. Resistivity uses assumed Rw=0.12 Ω·m, a=1, n=2, and m=2 for ordinary sands (2.15 for the tight layer), with a small shale-conductivity contribution. Shale resistivity is specified separately. Sonic uses a Wyllie-like fluid baseline and a separate illustrative gas correction; it is not a calibrated acoustic forward model.

The cemented layer has about 2.8% porosity and 45% calcite in its non-shale solid fraction. It is deliberately water-filled: high resistivity is caused by low porosity here. PHIE, SW, VSH, FACIES and ZONE are model truth. They must not be mistaken for properties inferred by the plotting tools.

## Expected display checks

The complete log scene has four tracks and seven curve instances: GR; RHOB/NPHI; LLD/LLS; RHOB/DT. GR uses a baseline of 75 gAPI. Resistivities use log scales from 0.2 to 2,000 Ω·m. Both crossplots have 4,001 numeric pairs; configured limits may clip points, so check visiblePairs separately.

![Synthetic 500–1500 m well with GR, RHOB, NPHI, resistivity and sonic tracks](four-track.png)Four-track display exported by v4. Orange/turquoise fills follow display-space left/right relationships.

![Density versus sonic slowness crossplot coloured by the known synthetic facies](density-sonic.png)DT–RHOB crossplot. The known FACIES code supplies the colour.

## References and limits

[SLB: Measuring Porosity Downhole](https://www.slb.com/resource-library/oilfield-review/defining-series/defining-porosity); [SLB: sandstone-compatible scale](https://glossary.slb.com/terms/s/sandstone-compatible_scale); [US EPA: Acoustic Logging](https://www.epa.gov/environmental-geophysics/logging-techniques-and-tools-acoustic-logging). These explain response principles; the generator’s numerical parameters are our illustrative choices.

Use the supplied LAS for exact reproduction. Re-running the generator under different numerical-library versions can change rounding; a different file fingerprint will require newly saved settings.