Lithology Interpretation

Lithology interpretation is the petrophysical step that turns raw well logs into a single lithology curve: every depth sample is assigned a lithotype code (for example sand, shale or limestone) by comparing the input curves against user-defined value ranges. The lithology curve is the basis for net-pay definition, facies modeling and property population, so it is best run early in the well-analysis workflow, immediately after the logs have been loaded and cleaned.

Launching the tool

Open the Petrophysics ribbon bar and click Lithology interpretation in the Execute group. Select the target well, or enable Batch calculation to process several wells or a well group from the Data Manager in one run. The full parameter reference is documented in the Lithology tool topic.

Recommended workflow

Prepare the logs first. Confirm the input curves are loaded, correctly named and free of null spikes. Repair problem curves in LAS editing and derive any missing inputs (for example shale volume) before interpreting lithology.
Choose discriminating curves. Pick the logs that best separate the expected lithotypes (typically gamma ray, density, neutron and resistivity) and set a minimum and/or maximum threshold for each.
Define the lithotypes. Set the number of lithotypes, name each one from the lithology map and enter its curve thresholds and match rule.
Restrict the interval. Use the depth filter (MD, TVD/TVDSS or marker ranges) to limit the interpretation to the zone of interest.
Run and QC. Run the calculation, then review the output lithology curve against the source logs and markers in the well log view. Adjust thresholds and re-run until the result is geologically consistent.

Recommendations

Calibrate thresholds against a key well with core or reliable cuttings before running in batch mode across the field.
Keep the number of lithotypes to the minimum that the logs can actually resolve; too many classes produce a noisy, unreliable curve.
Re-run lithology interpretation whenever the underlying curves are edited or new wells are imported so the lithology curve stays consistent with the log data.