Free Online LAS File Viewer and Well Log Petrophysics Tool

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No log loaded yet. Load the demo well or open a .las file. Files are parsed entirely in your browser and never uploaded.
Tracks left to right: gamma ray with clean and shale lines, deep resistivity on a log scale, density (red) with neutron (dashed blue) overlaid on compatible scales so gas shows as crossover, then computed effective porosity and water saturation with net pay flagged in teal. Adjust any parameter and press Compute to reinterpret instantly.

A well log viewer that runs in your browser

The tool above opens a LAS file, draws it as a proper four-track well log display, and then does the interpretation: shale volume from gamma ray, porosity from density and neutron, water saturation from the Archie equation, and net pay flagged against your cutoffs. Everything happens locally in your browser using the FileReader interface, so a confidential well log never travels to any server. If you do not have a file handy, the Load Demo Well button generates a realistic 300 meter log with a gas sand and a brine sand to explore.

Well log display with four tracks: gamma ray, deep resistivity, density-neutron overlay showing gas crossover, and computed water saturation with net pay flagged, next to the seven-step LAS interpretation workflow
From LAS file to pay flag: gamma ray, resistivity, density-neutron, and the computed saturation track with net pay in teal.

This is the second tool in the Geoscience Workbench, the suite linked in the bar at the top of the page. The SEG-Y viewer handles the seismic side; this one handles the wells; and the tools that follow connect the two.

How to open a LAS file

Click the file selector and choose your .las file. LAS, the Log ASCII Standard published by the Canadian Well Logging Society, is the plain-text format that nearly every logging contractor and data vendor uses for digital well logs, which is why the answer to how do I open a LAS file is usually just: with a text editor if you want to squint at numbers, or with a viewer like this one if you want to see the log. The parser reads the version, well, curve, and ASCII sections, honors the NULL value, and lists every curve it finds. The tool then guesses which curves are gamma ray, resistivity, density, and neutron from their mnemonics (GR, ILD, RHOB, NPHI and the common variants), and you can override any of the four with the dropdowns if your file uses unusual names.

From curves to answers: the petrophysics

The computation follows the standard quicklook workflow taught to every petrophysicist. Shale volume comes from the linear gamma ray index between your clean sand and shale baselines. Density porosity comes from the bulk density curve with your chosen matrix and fluid densities, averaged with neutron porosity where available and corrected for shale. Water saturation comes from the Archie equation with editable a, m, n, and Rw, which means you can also see immediately how sensitive your pay count is to a cementation exponent of 1.8 versus 2.2, a lesson usually learned the expensive way.

Reading the tracks

  • Gamma ray: low values are clean reservoir, high values are shale. The dashed orange lines mark your chosen clean and shale baselines.
  • Resistivity on a log scale: high resistivity in a clean rock suggests hydrocarbons; low resistivity suggests brine.
  • Density and neutron together: when the red density curve crosses left of the dashed blue neutron curve on these compatible scales, that crossover is the classic gas signature.
  • The computed track: effective porosity in teal, water saturation dashed purple, and every depth passing all three cutoffs flagged as net pay along the right edge.

Net pay and the cutoffs

The three cutoffs are where interpretation meets business. A depth counts as pay only if shale volume is below your Vsh cutoff, effective porosity is above your porosity cutoff, and water saturation is below your Sw cutoff. The summary cards report net pay thickness, the average porosity and saturation inside the pay, and the pay fraction of the logged interval, and the printable summary records the parameters used so the number can be reproduced. Export the computed curves as CSV to carry the interpretation into a mapping package or spreadsheet.

What this tool is for

Students learning log analysis, geologists who need a quick look at a well without a license server, and anyone who has been sent a .las file and wants to see the log rather than a wall of numbers. It reads standard unwrapped LAS 2.0 files, which covers the overwhelming majority in circulation. It does not replace a full petrophysics platform: there is no multi-well batch mode, no bad-hole editing, and thin beds deserve more care than a quicklook average. For the honest first pass that most decisions actually rest on, it does the job in about a minute.

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