Digital Wireline Logs
A practical reference for the LAS file format, composite log construction, and the quality-control standards that separate workstation-ready data from raw exports.
What is a LAS file?
LAS (Log ASCII Standard) is the de facto file format for digital wireline log data in the petroleum industry. Maintained by the Canadian Well Logging Society since 1991, LAS is a plain-text format readable by every petrophysical workstation: Petrel, Techlog, IP, Geolog, GeoFrame, Kingdom, OpenWorks.
A LAS file is organised into named sections, each beginning with a tilde-prefixed header (~V, ~W, ~C, ~A). The two versions in active use are LAS 2.0 (1996) and LAS 3.0 (2000); 2.0 covers single-pass wireline data, 3.0 adds support for multiple data sets, time-indexed measurements, and richer parameter blocks.
Anatomy of a LAS 2.0 file
The five sections of a LAS 2.0 file:
~V— Version. LAS version, single-line wrap convention.~W— Well information. Well name, API/UWI, location, datum, depth range, null value sentinel (e.g. -999.25).~C— Curve information. One row per curve: mnemonic, units, API code, description.~P— Parameter information. Acquisition parameters: tool string, mud weight, RM/RMF/RMC, surface temperature, BHT, run number, etc. Optional but commonly populated.~A— ASCII data. Tabular numeric data: depth column then one column per curve, separated by whitespace.
LAS 2.0 vs LAS 3.0
LAS 3.0 adds explicit "data set" partitioning so a single file can contain main wireline curves, dipmeter array data, processed curves, and core data side-by-side without ambiguity. It also formalises array curves (matrix data per depth, e.g. dipmeter pad readings) and time-indexed measurements (production logs).
Most production workflows still operate on LAS 2.0 because tooling support is universal and the format covers the wireline curve case without ceremony. We deliver LAS 2.0 by default and can produce LAS 3.0 on request, including for multi-pass logging suites.
Composite logs
A composite log is a single, depth-continuous LAS file built from multiple individual logging runs. A typical exploration well has 2–4 runs (e.g. surface section, intermediate section, deepest open hole, optional cased-hole production logs); each run produces its own LAS file with its own depth range, depth reference, and curve set.
Building a composite means resolving three classes of inconsistency:
- Depth shifts. Adjacent runs disagree on absolute depth by 0.1–3m due to cable stretch, temperature differences, and re-logging accuracy. The composite picks one reference (usually the deepest run), shifts the others, and records the shift applied per run.
- Curve overlap. Where two runs cover the same depth interval, the composite must choose which run's curve takes priority. We default to the deepest run on the rationale that calibration is best at the bottom; older composites sometimes splice run-by-run.
- Mnemonic drift. The same physical curve might be called
GR,GRS, orSGRacross runs depending on tool generation. The composite normalises to a canonical mnemonic and records the alias.
Done properly, a composite log lets a petrophysicist load one file per well and start interpretation. Done poorly, the depth shifts hide and the formation tops drift across the well by metres.
QC standards
"QC'd" is a marketing word that hides a wide range of practice. Here is what we mean by it, and what we'd expect from any provider:
Header validation
Header values cross-checked against an authoritative external register. In Australia that's the relevant state or territory geological survey: NOPSEMA, GSWA, GSV, GSQ, NTGS, MRT. We flag mismatches in the ~W section without silently overwriting; the customer sees the catalog value alongside the original.
Curve integrity
Each curve scanned for spikes (cable jerks, mud filtrate spikes), gaps (runs that didn't reach TD), null values (tool not deployed for that interval; the -999.25 sentinel), unit mismatches (depth in feet vs metres; resistivity in ohm-m vs ohm-ft), and impossible values (negative gamma ray counts, density >5 g/cc).
Depth alignment
Composite construction aligns runs to a single depth reference. Where runs disagree by more than the natural log-marker tolerance (~1m), the discrepancy is logged in the WDS comments and the chosen reference is recorded.
Documented, not silently fixed
This is the line most archives don't draw clearly. A spike removed without a comment is invisible to the customer. An issue documented — "DT spike at 2,415m removed by interpolation, original value 30 us/ft below trend" — lets the petrophysicist decide whether the fix is acceptable for their interpretation. Our well data summaries include this kind of provenance per well where applicable.
Common wireline curves
Gamma Ray
Natural radioactivity. Identifies shale (high GR) vs sand/carbonate (low GR). Typically the first curve any petrophysicist looks at.
Resistivity
Formation electrical resistance. Hydrocarbons resist current more than brine; resistivity contrasts indicate fluid type and saturation.
Sonic
Acoustic travel time through formation. Used for porosity, geomechanics, and seismic-to-well tie via synthetic seismograms.
Density
Bulk density from gamma scattering. Combined with neutron, gives porosity and lithology discrimination.
Neutron
Hydrogen index (porosity proxy). Cross-plotted with density to distinguish gas (low neutron, high density) from oil and water.
Caliper
Borehole diameter. Identifies washouts, breakouts, mudcake. Used to apply environmental corrections to other curves.
Spontaneous Potential
Naturally occurring electrochemical potential. Identifies permeable zones and provides shale-baseline reference.
Browse digital logs by basin
The most active basins in the archive. Each link goes to the full well list for that basin with map, table, and well-by-well download.
Want clean LAS data for your project?
Browse the archive on the map, request a quote for the wells you need, or licence the full corpus for ML training.