Track
A track in well log presentation is a vertical section of the log display dedicated to a particular set of data curves or annotation columns, dividing the printed or digital log into multiple parallel vertical channels each with its own scale, set of curves, and labeling — with the section being vertical in the sense that it extends along the depth axis of the log (which is conventionally oriented with depth increasing downward on the page); tracks are conventionally numbered from left to right across the page, with Track 1 (leftmost) typically reserved for gamma ray and caliper curves with the depth values displayed alongside, the depth track itself between Tracks 1 and 2 showing measured depth in feet or meters as a continuous numerical scale, Track 2 displaying porosity-related curves (density, neutron, sonic, NMR), Track 3 displaying resistivity curves (shallow, medium, deep induction or laterolog), and additional tracks (4 and beyond) used for image logs, formation imager rosettes, dipmeter tadpole displays, or other specialized data; curves drawn within a track are normally blanked off (clipped) when their values exceed the track's allotted scale range, preventing cross-track interference and maintaining clean log presentation; the track structure of a log is determined by the logging software (Schlumberger Techlog, Halliburton DecisionSpace Petrophysics, Senergy Interactive Petrophysics) using configurable templates that match standard industry conventions while allowing customization for specific operator preferences or specialty log types.
Key Takeaways
- Standard four-track log format adopted by the industry as the conventional triple-combo presentation organizes log curves by measurement type into a recognizable layout that experienced petrophysicists can interpret rapidly — Track 1 (left, typically 2.5 inches wide on hardcopy logs) contains gamma ray (linear scale 0 to 150 API units), caliper (with bit size shown), and SP if recorded; the depth track between Tracks 1 and 2 shows measured depth (typically 1 inch wide for vertical wells, scale of 1:240 for normal display or 1:600 for compressed display); Track 2 (typically 2.5 inches wide) contains density (1.95 to 2.95 g/cc), neutron (45 to -15 limestone porosity units, displayed reverse-scale), and PEF (0 to 10 barns/electron); Track 3 (rightmost on triple-combo, typically 2.5 inches wide) contains resistivity curves (deep induction, medium induction, shallow MSFL/SFL) on logarithmic scale 0.2 to 2000 ohm-m; the standard arrangement allows quick visual identification of pay zones (high resistivity Track 3 + density-neutron crossover Track 2 + clean gamma ray Track 1 = oil/gas pay; high resistivity Track 3 + density-neutron crossover Track 2 + high gamma ray Track 1 = potential shaly pay requiring further analysis).
- Image log presentation tracks display borehole image data (FMI, FMS, EMI, OBMI, UBI) as colored or grayscale unrolled images that show the borehole wall as if cut along an azimuth and unrolled flat — image tracks are typically wider than standard tracks (3 to 5 inches) to provide adequate angular resolution, with the horizontal axis representing azimuth (0 to 360 degrees) and the vertical axis representing depth; image data displayed in tracks reveal sedimentary features (bedding planes, crossbedding, lamination), structural features (fractures, faults, drilling-induced features), and lithology variations (carbonate-shale boundaries, conglomerate clasts, unconformities); image log interpretation includes manual or automatic picking of dipping features, with the resulting dip and dip direction displayed in adjacent tracks (typically tadpole displays where each pick is shown as a circle with a tail indicating dip direction at the depth of the picked feature); modern image log displays integrate multiple image curves (high-resolution, medium-resolution, conductivity, capacitance) into composite tracks that provide the most complete visualization of the borehole wall.
- Annotation tracks include the depth track itself, formation top labels at recognized formation tops, perforation interval annotations on completion logs, casing collar locator (CCL) markings on cased-hole logs, and zone labels assigned by the petrophysicist during interpretation — annotation tracks are typically narrow (0.25 to 0.5 inch wide) and contain text or symbols rather than continuous curves; the depth track provides the spatial reference for all log data and is typically displayed in measured depth (MD) with optional secondary scales for true vertical depth (TVD) and sub-sea depth (TVDSS) in deviated wells; formation top picks displayed in annotation tracks are the operator's interpreted formation boundaries based on log signature recognition and correlation to offset wells, providing the stratigraphic framework for petrophysical interpretation; perforation tracks display the as-completed perforation intervals as solid bars or schematic representations of perforation density, allowing the petrophysicist to relate log-derived petrophysical properties to specific producing zones.
- Custom tracks for specialty logs are created in modern logging software to display the unique outputs of specialized formation evaluation programs — production logging tracks include holdup meter outputs (water holdup, oil holdup, gas holdup) typically displayed as colored bars from 0 to 100 percent, spinner flowmeter velocity profile, and computed phase flow rates; NMR logging tracks include the T2 distribution as a colored shaded display, free fluid index, bulk volume of irreducible water, total porosity, and effective porosity; mud logging tracks include hydrocarbon gas detector responses (total gas, C1 through C5 ratios, fluorescence intensity), penetration rate, and lithology percent estimates from cuttings analysis; dipmeter and tadpole tracks display the dip magnitude and azimuth of recognized formation features as scatter plots with each point representing a single picked feature; custom track design is part of every major logging program's interpretation deliverable, with the specific track layout chosen to support the formation evaluation objectives of the program.
- Digital LAS file format and track interpretation in modern software preserves the data as columnar values rather than as a fixed track layout — the LAS file (Log ASCII Standard, developed by the Canadian Well Logging Society and now the dominant industry digital format) stores curves as named columns indexed by depth, with the track layout being a presentation choice in the visualization software rather than a fixed property of the data; this separation of data from presentation allows the same log data to be displayed in different track configurations to emphasize different interpretation aspects, and allows quantitative analysis (crossplots, histograms, statistical analysis) on the curve data without regard to its original track presentation; LAS file headers document the curves recorded in each well and their units, scales, and descriptions, enabling automated track template selection by interpretation software when the file is opened; modern petrophysical software (Techlog, IP, GeoFrame) supports both fixed standard track templates and user-customized templates, with template libraries shared across operators within companies for consistent log presentation across thousands of wells in a development program.
Fast Facts
The standard track layout for well logs was established by the major service companies (Schlumberger, Halliburton, Baker Hughes/now Lufkin Industries, Western Atlas/now Baker Hughes) in the 1970s and 1980s as the triple-combo log (gamma ray + porosity + resistivity in the standard 4-track format) became the industry-standard formation evaluation logging package. The widths of tracks (2.5 inches on hardcopy at 1:240 vertical scale) and the conventional positioning of curve types within each track are the result of decades of industry practice and accommodate the typical dynamic range of each measurement type while maintaining the visual conventions that experienced petrophysicists rely on for rapid log inspection. Modern digital logging systems and on-screen log displays can present logs at any track width and any vertical scale, but the conventional 4-track layout remains dominant because of its familiarity and the speed with which experienced petrophysicists can interpret the standard format. The Society of Petrophysicists and Well Log Analysts (SPWLA) has published guidelines for log presentation that codify the standard track layout, providing a reference for the industry standard that continues to evolve with new measurement types.
What Is a Track in Well Log Presentation?
A printed or digitally displayed well log is a long, narrow document with depth increasing downward and multiple parallel columns of data running vertically along the depth axis. Each of these vertical columns is a track. The track is the basic organizational unit of log presentation, dividing the visual display into manageable channels each with its own scale, set of curves, and labeling. A well log typically has 3 to 5 main tracks plus a narrow depth track providing the spatial reference, and the curves within each track are chosen by convention to support specific aspects of formation evaluation interpretation.
The track convention is essentially universal in modern well logging, with the standard four-track layout (gamma ray and caliper in Track 1, depth in the depth track, density and neutron in Track 2, resistivity in Track 3) recognizable to any petrophysicist in any country. This shared visual language allows logs from one operator's wells to be inspected and interpreted by petrophysicists from any other operator without explanation of the layout — a Schlumberger gamma-ray-density-neutron-resistivity log from the Permian Basin looks fundamentally the same as a Halliburton log from Saudi Arabia, both using the same track conventions to display equivalent measurements. This standardization is a major contributor to the productivity of the global formation evaluation workflow.
Standard Track Layout in Modern Petrophysical Software
A modern petrophysical workflow begins with importing LAS-format log data into the interpretation software, where the software automatically applies a default track template based on the curves available in the file. The default template typically follows the four-track standard for triple-combo logs, with additional tracks added for image logs, NMR logs, or other specialty data when those curves are present. The petrophysicist can customize the track layout by adjusting curve scales, adding or removing curves from tracks, changing colors, and adding annotation tracks for formation tops, perforations, or interpreted zones. The customized layout is saved as a template and reused on subsequent wells in the same field, ensuring consistent presentation across the field and supporting cross-well comparison. The interpretation outputs (computed water saturation, effective porosity, lithology percentages, net pay flags) are displayed in additional tracks specific to the interpretation, with the original measured curves preserved alongside for quality control and reinterpretation as needed. The completed log document is exported as PDF for distribution to non-software users (drillers, geologists, completion engineers) while preserving the LAS file for future quantitative analysis.
Track Conventions Across International Logging Practice
Canada (AER / WCSB): AER's well log submission requirements specify that all logs submitted in digital LAS format must include the standard triple-combo log curves, with the resulting display following industry-standard track conventions; CWLS (Canadian Well Logging Society) and SPWLA-Canada chapters maintain the educational and certification programs that train Canadian petrophysicists in the standard log layout; AER's online well database displays logs from over 500,000 WCSB wells using the standard track convention, allowing rapid inspection and comparison across the basin's massive cumulative drilling history.
United States (API / BSEE): API and SPWLA standards define the standard log presentation conventions used by US service companies and operators, with the four-track layout being the industry-wide default for conventional logging programs; LAS file format (originated in Canada but adopted globally) is the standard digital format for log data exchange, supporting standardized track presentation regardless of which software is used for visualization; BSEE's offshore log submission requirements include digital LAS files following the same standardized format used onshore, ensuring consistency between onshore and offshore log archives.
Norway (Sodir / NORSOK): NCS log submission requirements follow industry-standard track conventions with the additional requirement that all logs include the directional survey data and depth-conversion information needed to relate measured depth to true vertical depth subsea (TVDSS) for the typically deviated NCS wells; Sodir's national well database stores logs in LAS format with standardized header information that supports automated track template selection during data retrieval and visualization.