The Lithology interpretation tool assigns a lithotype code to every depth sample of a well by comparing the input well logs against user-defined value ranges. The result is a single lithology curve where each sample carries the code of the dominant lithotype (for example sand, shale, limestone).

The tool can be applied to a single well or in batch mode, allowing users to process all wells or selected wells from the Data Manager.

Open the Petrophysics ribbon bar and click Lithology interpretation. Select the target well (or enable Batch calculation to process a well group), then define lithotypes and run the calculation.

Input Parameters

• Well selection: Choose one well or enable Batch calculation to process multiple wells or a well group from the Data Manager.
• Depth filter: Define the interpretation interval using MD range, TVD/TVDSS range, or marker ranges.
• Number of lithotypes: Defines how many lithotype rows appear in the Input lithotypes list.
• Lithotype name: Select the lithotype label from the predefined lithology map.
• Input curves: All available curves from the current project can be selected for lithology identification.
• Curve thresholds: Define minimum and/or maximum values for each selected curve.
• Match rule: Defines how input curves are evaluated for a lithotype.
• Threshold: Used only in Weight mode. Defines the minimum accumulated score required to assign the lithotype.
• Conflict resolution for lithotypes: Defines how overlapping lithotype matches are handled.
• Output curve: Name of the resulting lithology curve. Default is Lithology.

Templates and history

The wizard stores previously used lithotype definitions so they can be reapplied without re-entry:

• Save template — stores the current lithotype list under a user-supplied name for reuse in other projects or wells.
• Apply template — loads a saved template or a recent entry from the wizard's history into the current session.

Match Rules

AND

All selected curves must satisfy their conditions for the lithotype to be assigned.

Algorithm

1. Evaluate all selected curves.
2. Compare curve values against Min/Max thresholds.
3. If all curves match:

1. If at least one curve fails:

OR

At least one selected curve must satisfy its condition for the lithotype to be assigned.

Algorithm

1. Evaluate all selected curves.
2. If any curve matches:

1. If no curves match:

Method Priority

Curves are evaluated in user-defined order. The first matching curve defines the lithotype.

Algorithm

1. Evaluate curves from top to bottom.
2. If the current curve matches:

1. If the curve fails:

1. Missing curves are skipped.
2. If no curves match:

Curve availability behavior

Weight

Each curve contributes a partial score toward lithotype identification.

Core conditions

• All weights must sum to 1.0.
• Only matched curves contribute their weights.
• The final score is compared against the Threshold value.

Algorithm

1. Evaluate all selected curves.
2. Add weights of matched curves.
3. Calculate the total score.
4. Compare the score against Threshold.
5. If score ≥ Threshold:

1. If score < Threshold:

Conflict Resolution for Lithotypes

When several lithotypes match the same depth sample, the wizard resolves the conflict using one of the following modes.

Lithotype priority

The lithotype higher in the lithotype list has higher priority.

Algorithm

1. Evaluate all lithotypes.
2. If multiple lithotypes match:

Undefined

If multiple lithotypes match:

• the sample is written as Undefined.

This mode is useful for manual review and interpretation refinement.

Displaying lithology in the Well Correlation view

In the Well correlation view, right-click the curve header, open Curve Settings and set the Curve Type to Lithology. The curve menu then offers a Lithology Map action for assigning a color and fill pattern to each lithology class (for example clay, shale, sandstone, limestone, dolomite). See Working with Palettes for details.

See Also

• Petrophysics
• Porosity
• Shale Volume
• Saturation
• Data manager
• Well correlation view
• Working with Palettes