Model reservoir saturation using dependable inputs and checks. Track assumptions quickly with engineering-friendly calculation panels. See instant results above, then export reports effortlessly today.
| Case | Rt (ohm-m) | Rw (ohm-m) | Porosity φ | a | m | n | Expected Sw (%) |
|---|---|---|---|---|---|---|---|
| Sandstone A | 18.0 | 0.12 | 0.22 | 1.0 | 2.0 | 2.0 | ~26.4 |
| Sandstone B | 8.5 | 0.15 | 0.18 | 1.0 | 2.0 | 2.0 | ~52.1 |
| Carbonate C | 30.0 | 0.10 | 0.12 | 1.0 | 2.2 | 2.0 | ~45.1 |
Expected values are illustrative and depend on selected exponents and clean-formation assumptions.
Archie Equation
Sw = ((a × Rw) / (Rt × φm))1/n
Sw(%) = Sw × 100
This model is generally applied to clean formations. Shaly sands often require modified equations (such as Simandoux or Indonesia models) for better estimates.
Water saturation is a key petrophysical indicator used to estimate movable hydrocarbon volume and support completion planning. Engineers compare saturation with porosity, permeability, capillary pressure, and production tests before decisions. A reliable estimate reduces uncertainty in net-pay selection, improves reserve classification, and strengthens economic screening. This calculator groups Archie inputs into one workflow so teams can test assumptions and document consistent calculations across wells. It also improves communication between geology and engineering teams.
The largest source of error is usually input quality, not arithmetic. True formation resistivity should be corrected from logs, and water resistivity must represent formation conditions rather than surface values. Porosity is entered as a fraction, and Archie constants should match rock type. For clean sandstones, a=1, m=2, and n=2 are common starting points, but field calibration remains important. Clay-rich formations may require non-Archie methods and shale corrections for estimates.
The calculator reports water saturation, hydrocarbon saturation, and an intermediate ratio for review. High water saturation often indicates limited hydrocarbon potential or water-prone intervals, while lower values may suggest better charge. However, saturation alone should not drive completion decisions. Interpret results with permeability trends, fluid contacts, pressure behavior, and test data. Values above 100% usually indicate inconsistent inputs or unsuitable assumptions and should be validated before reporting. Use runs to test uncertainty ranges.
A common use case is scenario testing in review meetings. Teams can hold Rt and porosity constant, then vary Rw or Archie exponents to evaluate sensitivity. This reveals whether interval ranking is stable or highly assumption-dependent. CSV export preserves a session log for comparison, peer review, or reconciliation with updated interpretations. The print-to-PDF option is useful for technical notes, drilling reports, and screening summaries. It supports sharing during approval discussions.
For professional use, maintain a input sheet for each field, including approved Rw values by zone and recommended Archie constants by lithology. Validate porosity source and unit conventions before entry. Keep a record of calculated saturation against production outcomes to improve calibration. This calculator supports repeatable estimation, but stronger results come from disciplined data management and periodic validation. Consistent workflows improve confidence, reduce rework, and support multidisciplinary decisions. Document assumptions beside every exported result.
It is the fraction of pore space occupied by water. A value of 0.30 means 30% of pore volume contains water under the model assumptions.
Archie calculations use porosity as a fraction. Enter 22% porosity as 0.22 to avoid scaling errors and incorrect saturation results.
Use caution. Archie works best in clean formations. Shaly intervals may require conductive-shale corrections, such as Simandoux or Indonesia methods.
Usually due to input mismatch, incorrect units, unrealistic constants, or poor Rw estimation. Review Rt, Rw, porosity fraction, and Archie exponents.
Yes, mainly through water resistivity selection. Rw should reflect formation temperature conditions, because resistivity changes significantly with temperature.
It is estimated as 1 minus water saturation, displayed as a percentage. This quick metric helps compare potential hydrocarbon-filled pore volume.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.