geology · stratigraphic
Average Thickness & Porosity (Multi-Zone)
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Inputs
Paste one row per line — separate columns with a comma or tab: Thickness (ft), Porosity (fraction)
⚠ Needs at least 2 valid rows to calculate — 0 so far.
Description
Averages thickness and porosity across multiple zones or multi-well control points using the standard reservoir/log-analysis conventions: a simple arithmetic mean for thickness, and a thickness-weighted mean for porosity so that thicker, more pore-volume-significant zones contribute proportionally more than thin ones. Feeds directly into net_rock_volume/gross_rock_volume or the ooip/giip volumetric chain, whose own porosity input is already documented as 'typically a thickness-weighted average from log analysis.'
Variables
| Symbol | Unit | Description |
|---|---|---|
| havg | ft | Average Thickness |
| φavg | fraction | Average Porosity |
| h, φ | — | One row per zone or multi-well control point: thickness and its associated porosity. Paste at least 2 zones — average thickness is the simple arithmetic mean across rows, and average porosity is thickness-weighted so thicker zones count more, the standard log-analysis convention for a multi-zone porosity average. |
Assumptions
- Each row is a genuinely distinct zone or control point over the same averaging interval — not overlapping or double-counted thickness.
- Porosity values are already effective (or total, consistently) porosity from log analysis — this calculator does not itself derive porosity from logs.
- Thickness-weighting is the correct convention for the intended downstream use (e.g. feeding a volumetric estimate); a purely areal/volume-weighted average would require additional per-zone area data this calculator does not take.
Limitations
- Average thickness is a plain arithmetic mean across rows — it does not itself weight by each zone's areal extent, which would require a genuine multi-well map, not a single scalar per zone.
- Thickness-weighted average porosity is the standard convention for feeding a single-value volumetric calculation, but arithmetic and areal/volume-weighted averages are also real, cited conventions that can diverge from this result — confirm which convention a downstream reference (e.g. a reserves report) expects before comparing values directly.
- Does not itself validate that the pasted zones are non-overlapping or drawn from a consistent depth/areal basis — garbage in, garbage out for zone selection.
Use Cases
- → Feeding a volumetric estimate: Reduce several net-pay-zone thickness/porosity pairs from log analysis into the single average thickness and average porosity values gross_rock_volume, net_rock_volume, or ooip/giip expect as scalar inputs.
- → Multi-well reservoir characterization: Combine thickness and porosity picks from several wells across a field into representative field-average values for early-stage volumetric screening.
Related Calculations
Region Notes
Global
Thickness-weighting for average porosity is the standard convention taught in basic well log analysis courses and used throughout volumetric reserves estimation — but always confirm which averaging convention a specific field's reserves report or reservoir model actually uses before treating this result as directly comparable.
References
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