The Shale Volume wizard estimates the fraction of shale within a formation based on well log data. It supports several industry-standard methods using Gamma Ray (GR) or Spontaneous Potential (SP) logs.
The output is a Vshale (Vsh) curve that represents the volumetric proportion of shale along the wellbore.
Input Parameters
•Well selection: Choose one well or activate Batch calculation to process all wells or a selected group from the Data Manager.
•Depth filter: Define the interval for calculation by using MD range, TVD/TVDSS range, or by selecting the depth between markers.
•Curve selection: Select the log to be used (Gamma Ray or SP).
•Parameter limits: Set clean and shale reference values for the chosen curve (manual or automatic).
•Output curve: Define the name for the resulting shale volume log.
Each method generates a Vshale (Vsh) log, displayed alongside the input curve for visual comparison.
Users can review results on the Input/Output panel, adjust parameters, rename the output curve directly in the wizard, and click Save to store it in the project.
Calculation Methods
1. Linear Index (GR)
This is the simplest approach assuming a linear relationship between Gamma Ray values and shale content.
Use:
•Quick estimation for clean sand–shale sequences.
•Best applied when GR response is approximately linear with shale content.
2. Steiber (GR)
Introduces a non-linear correction to better reflect compaction and radioactive mineral effects.
Use:
•Suitable for mixed lithologies and compacted formations.
•Reduces overestimation of shale content in clean sands.
3. Clavier (GR)
An empirical formula that smooths the transition between clean and shaly intervals.
Use:
•Appropriate for moderately shaly formations.
•Often applied to Tertiary clastic reservoirs.
4. Larionov (Tertiary Rocks) (GR)
Developed by Larionov (1969) for young sedimentary sequences with low compaction.
Use:
•Recommended for Tertiary rocks and soft sediments.
•Corrects for overestimated shale content in younger formations.
5. Larionov (Older Rocks) (GR)
Modified Larionov model for compacted and older formations (e.g., Paleozoic–Mesozoic).
Use:
•Suitable for consolidated rocks and older stratigraphic units.
•Provides more realistic shale values in deep formations.
6. SP Baseline Method (SP)
Uses Spontaneous Potential (SP) log instead of GR for shale estimation.
The method compares the measured SP curve with reference clean and shale baselines.
Use:
•Useful when GR data is unavailable or unreliable.
•Common in older wells with limited logging suites.
