Water Saturation Calculator
Calculate Sw using the Archie equation, Indonesian (Poupon-Leveaux) model for shaly sands, and Simandoux equation.
Archie Equation (1942)
Sw = (a × Rw / (φm × Rt))1/n
Results
Water Saturation (Sw)
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Hydrocarbon Sat. (Sh)
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Bulk Volume Water (BVW)
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Formation Factor (F)
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How this was calculated
Archie (1942): Sw = (a * Rw / (phi^m * Rt))^(1/n). Valid for clean (non-shaly) formations. Parameters a, m, n are lithology-dependent.
Indonesian (Poupon-Leveaux, 1971): Extends Archie for shaly sands using Vsh and Rsh. Uses iterative solution for Sw.
Simandoux (1963): Quadratic model for shaly sands. Solves Sw from: 1/Rt = phi^m*Sw^2/(a*Rw) + Vsh*Sw/Rsh.
Typical values: a=1, m=2, n=2 (Archie defaults). Humble formula: a=0.62, m=2.15. Carbonates: a=1, m=2.0-2.5.
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Book a free strategy call →Understanding Water Saturation (Sw) in Petrophysics
Water saturation (Sw) is one of the most critical petrophysical parameters, representing the fraction of pore space occupied by water. The complement (1 - Sw) gives hydrocarbon saturation, which directly drives volumetric reserves estimates and completion decisions.
The Archie equation (G.E. Archie, 1942) is the foundation of resistivity-based Sw calculation: Sw = (a * Rw / (phi^m * Rt))^(1/n). It assumes the rock matrix is non-conductive and all conductivity comes from formation water. This works well in clean sandstones and carbonates but fails in shaly formations where clay minerals contribute additional conductivity.
For shaly sands, the Indonesian (Poupon-Leveaux) and Simandoux equations account for shale conductivity through Vsh and Rsh parameters. The Indonesian equation is widely used in Southeast Asian formations (hence the name) and handles moderate to high shale volumes effectively. Simandoux provides a quadratic solution that is simpler to implement but may underestimate Sw in highly shaly zones.
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