Lithology Interpretation

Lithology interpretation is the petrophysical step that turns raw well logs into a single lithology curve: each sample in the selected interval is assigned a lithotype code (for example sand, shale or limestone) by comparing the input curves against value ranges that can be adjusted for each lithotype. 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 in the Lithology 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). When you add a curve with valid samples in the displayed well and current processing interval, the wizard fills its Min and Max values automatically.
Define the lithotypes. Set the number of lithotypes, name each one from the lithology map, review or adjust its curve thresholds, and choose a match rule.
Restrict the interval. Use MD range, TVD range, TVDSS range, Markers range or Zones range to limit the interpretation. With Zones range active, select one or more zones; the existing lithotype rules are applied only inside valid selected intervals and values outside them remain undefined.
Run and QC. Click Run to update the Input/Output preview. Compare the output lithology curve with the input logs and selected intervals, adjust thresholds if needed, and run again until the result is satisfactory.
Save the checked result. After a successful Run, make sure Output curve has a name, then click Save to store the checked lithology curve in each successfully processed well. For the output setting and save controls, see the Lithology topic.

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.