Heading: Well Log Header Records, Mud Property Documentation, and WCSB Log Filing Requirements

In well logging, the heading is the first page or pages of a log print, the section that records the identifying and reference information about the well, the survey, the mud properties, and the operational conditions under which the log was acquired. It is the metadata of the log, and although it carries no curve data of its own, it is the part of the document that makes every measurement on the following pages interpretable, traceable, and legally usable. A wireline or logging-while-drilling heading typically captures the well name and unique well identifier, the legal land description, the operating company and the logging contractor, the rig and the elevation references, the casing and bit sizes, the depth driller and depth logger, the type of logging run and the tools strung together, the date and time, and a detailed block of borehole-fluid information. The mud data on a heading is not decorative: the resistivity of the mud, the mud filtrate, and the mud cake at measured temperature, written as Rm, Rmf, and Rmc, are direct inputs to resistivity-log interpretation and to the calculation of water saturation, so an analyst reading an old log first turns to the heading to recover the fluid parameters that the original engineer measured at the wellsite. The heading also records the maximum recorded temperature, which is used to correct resistivities and other temperature-sensitive readings to formation conditions, along with the mud weight, viscosity, fluid loss, pH, and the source of the sample. Elevation references matter because every depth on the log is hung from a defined datum such as kelly bushing or ground level, and a mismatch between the log datum and the datum used by offset wells will misalign correlations across a field. In the Western Canadian Sedimentary Basin, log headings carry particular regulatory weight because operators must file logs with the provincial regulator, and the heading is the record that ties a curve set to a specific licensed well, a specific run, and a specific set of acquisition conditions. The AER, under its data submission requirements, and the BCER expect complete and accurate log headings as part of the well-record filings that populate the public data infrastructure relied upon by every geologist and engineer working the basin. A heading with a wrong unique well identifier, a transposed elevation, or missing mud parameters degrades the value of an otherwise perfect log, which is why quality control of the heading is a standard step before a log is accepted. The standard digital format for log data, the LAS file used across the WCSB, mirrors the paper heading in its well, parameter, and curve information sections, carrying the same metadata into every interpretation workstation. The heading connects directly to well log, mud filtrate resistivity, and kelly bushing, the datum from which logged depths are commonly referenced.

What The Heading Records

A complete log heading documents the well and survey identity, the operator and logging contractor, the rig name, casing and bit sizes, the depth interval logged, the tool string and run number, and the date and time of acquisition. Below that sits the borehole-fluid block: mud type, density, viscosity, fluid loss, pH, and the all-important Rm, Rmf, and Rmc resistivities with the temperature at which each was measured, plus the maximum recorded temperature from the logging run. Elevation references, kelly bushing height, and permanent datum complete the page. On a WCSB well, the unique well identifier and legal subdivision tie the document into the AER and BCER well-record databases that every offset interpretation relies on.

Why Heading Errors Are Expensive

A flawed heading can quietly poison an interpretation long after the logging crew has left. A transposed kelly-bushing elevation shifts every depth and throws a correlation off by metres, breaking a field cross-section. A wrong mud-filtrate resistivity skews the water-saturation calculation and can turn a pay zone into apparent water or the reverse. A missing or incorrect unique well identifier orphans the log in the regulator's database so that offset operators never find it. Because these errors are cheap to prevent and costly to discover years later, WCSB log analysts treat heading verification as a mandatory step before any LAS file is loaded into a mapping or petrophysical project.

Related Terms

The heading is the front matter of a Well Log, the curve record whose measurements it makes interpretable, and it preserves the Mud Filtrate Resistivity needed to compute water saturation from resistivity curves. Its depth entries reference the Kelly Bushing datum from which logged depths are hung, and the whole record supports Formation Evaluation, the petrophysical workflow that turns logged measurements into porosity, saturation, and pay estimates across WCSB reservoirs.

WCSB Field Scenario: A Datum Error On A Cardium Correlation Near Pembina

A geologist building a Cardium cross-section across the Pembina field in west-central Alberta found one well stubbornly out of zone, with the Cardium sandstone appearing several metres high relative to every offset. Curve quality was excellent, so the problem was not the log. Checking the heading revealed the kelly-bushing elevation had been entered using ground level rather than the rig floor, shifting the entire depth track. Correcting the datum on the LAS header realigned the well, and the sand fell back into structural conformity with its neighbours.

The fix cost nothing but an hour of quality-control time, yet it prevented a mismapped structure that could have steered a CAD several-million-dollar development location to the wrong spot. The episode reinforced the field rule that heading verification precedes any correlation work in the basin.