LAS Format

Introduction

LAS is the standard geophysical log file format supported by the Canadian Well Logging Society. The LAS standard was introduced by the Canadian Well Logging Society in 1989 to standardize the organization of digital log curve information for personal computer users. It did this very successfully and the standard became popular worldwide.

The LAS (Log ASCII Standard) is now widely accepted for the transfer of geophysical log data. Version 1.2 was the first version and followed in September 1992 by version 2.0 to address some inconsistencies. A more versatile version LAS 3.0 was released in 1999 however at present, LAS 2.0 remains the dominant product.

Geo-log 4 supports LAS Version 2.0 format.

Software

Software applications exist to check LAS files syntax. Those can be found on CWLS.org website page LAS (Log ASCII Standard) under LAS Software section.

The Certify Software was designed to verify that files meet the LAS standard and will identify any error encountered. The checks are based on structure, not content. That is, it will not flag an empty well name field, but will recognize that required sections are missing or if a line is not structured correctly.

LAS 2.0 format overview

• A LAS file is a structured ASCII file containing log curve data and header information. The header information is located at the beginning of the file and followed by curve data.

• The ASCII character set is limited to ASCII 13 (carriage return), ASCII 10 (line feed), and ASCII 32 to ASCII 126 inclusive. All other ASCII characters are not allowed.

• Each LAS 2.0 file contains only one continuous interval in the data section. For example, a repeat section would make up one file and the main pass another.

• LAS files end in ".las" so that they can be easily recognized.

• Each LAS file consists of sections. Sections begin with a header line defined as beginning with the "~" tilde character when it occurs as the first non-space character on a line. The character immediately following the tilde character defines the section with the remainder of the line being ignored. The characters "V", "W", "C", "P", "O", and "A" are reserved in the LAS 2.0 standard. The sections defined by the LAS 2.0 standard are limited to one occurrence per file. Customer defined sections are permitted but must be located after the first section "~V" and before the last section "~A".

• Two flags are used in LAS files:
  1. "#" signifies a comment line when used as the first non-space character on a line and
  2. "~" signifies the beginning of a section when used as the first non-space character on a line.
• The sections "VERSION", "WELL", "CURVE" and "PARAMETER" use line delimiters. The delimiters are:
  1. first dot "." in a line
  2. first space " " after the first dot in a line and
  3. the last colon ":" in a line.

Geo-log 4 compatible example

Below is an example of LAS 2.0 files that can be imported into Geo-log 4, see Uploading records.

• Natural radioactivity log

Well Information

The section ~Well Information identifies the well (borehole), its location and indicates the start and stop depths of the file. The LAS 2.0 format does not force the user to enter consistent value in the text fields (WELL, FLD, …). Nevertheless the lack of value seriously harms the record identification in Geo-log 4. That is why we advocate their systematic entry.

Curve Information

The section ~Curve Information describes the curves and its units in the order they appear in the ~A section of the file. Geo-log 4 only recognizes curves as a function of depth.

Only the GR curve (Gamma Ray) can currently be imported in Geo-log 4. If you need other curves, please contact us.