Free Tool
Free Online LAS File Viewer
Open a LAS 1.2 or 2.0 well log and see it plotted in seconds: gamma ray, resistivity, density, neutron or any curve in the file. No sign-up, and your file never leaves your computer.
Drop a .las file here
LAS 1.2 or 2.0, up to 200 MB. Read in your browser, never uploaded.
The sample is synthetic, not from a real well. Download it to see the format.
How it is calculated
LAS is the Canadian Well Logging Society's plain-text format for well logs. The viewer reads it section by section, the way the standard lays it out:
~Version VERS 2.0, WRAP NO ~Well STRT / STOP / STEP, NULL -999.25, WELL, FLD, COMP, UWI ~Curve DEPT.M GR.GAPI RDEP.OHMM RHOB.G/C3 ... (column order) ~Parameter BS, BHT, mud properties ... ~ASCII one row per depth, one column per curve
Each header line is MNEMONIC.UNIT VALUE : DESCRIPTION. The data is read as a stream of numbers and regrouped by the number of curves, which is how wrapped files (one depth spread over several lines) are handled. Values equal to the file's NULL become gaps.
To keep large files fast, each track draws about one point per pixel of height, keeping the minimum and maximum of every interval so thin beds and spikes are never smoothed away.
Common questions
No. The file is read by your browser with the FileReader API and parsed on your own computer. Nothing is sent to GeoMaster or any other server, so confidential well data stays on your machine. You can disconnect from the internet after the page loads and the viewer still works.
LAS 1.2 and LAS 2.0, the versions almost every logging contractor and well data system exports, including wrapped files (WRAP YES). LAS 3.0 files, which use sections such as ~Log_Definition and comma-delimited data, are reported as unsupported rather than read incorrectly.
The viewer reads the NULL value from the ~Well section (usually -999.25) and treats every matching value as missing, whatever its decimal formatting. Missing intervals show as gaps in the curve rather than as spikes to the null value, and the curve table reports how many samples are missing.
Resistivity readings span several orders of magnitude, from below 1 ohm·m in water-bearing sands to hundreds or thousands in hydrocarbon zones and tight rock. A logarithmic scale keeps both ends readable. The viewer recognises common resistivity mnemonics such as RDEP, ILD, LLD and RT and opens them on a 0.2 to 2000 ohm·m log scale; you can switch any track between linear and log.
Yes. Download CSV writes the full data table with one column per curve and the unit in each header, with missing values left blank so spreadsheets do not treat -999.25 as a real reading.
A LAS (Log ASCII Standard) file is a plain-text well log format from the Canadian Well Logging Society. It has a ~Version section, a ~Well section with the well name, depth range, step and null value, a ~Curve section listing each curve in column order with its unit, optional ~Parameter and ~Other sections, and the ~ASCII data table, one row per depth.
From a log plot to a steered well
GeoMaster imports the same LAS files, correlates them against a type well with GeoMatch, and tracks the well against its plan in DrillTracker, in your browser.
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