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Archie Water Saturation Calculator engineering
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Archie Water Saturation Calculator

Petrophysics & well logging: Determine water saturation (S_w), hydrocarbon saturation (S_hc), formation factor (F), and bulk volume water (BVW) using Archie classic empirical law.

Petrophysical Log Parameters

From density / neutron logs
Uninvaded formation resistivity
Saline water resistivity at T_res
Archie standard = 1.0 (Humble = 0.62)
Consolidated sand ~2.0, carbonate ~2.2
Typically ~2.0 for water-wet rocks

Fluid Saturation & Rock Properties

Water Saturation (S_w)
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Hydrocarbon Saturation (S_hc)
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S_hc = 1 - S_w (Pay Zone)
Formation Factor (F)
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F = a / Φ^m
100% Water Resistivity (R_o)
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R_o = F · R_w
Bulk Volume Water (BVW)
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BVW = Φ · S_w
Resistivity Index (I)
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I = R_t / R_o

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Frequently Asked Questions

What is the significance of the cementation exponent m?

The cementation exponent m reflects the pore geometry and degree of rock consolidation. In unconsolidated sands, m ≈ 1.3 to 1.6. In clean, consolidated sandstone, m ≈ 2.0. In vuggy or fractured carbonates, m can range from 1.8 up to 2.8.

Why can Archie equation fail in shaly sands?

Archie assumed that electrical conduction occurs exclusively through saline pore water. Clay minerals in shales conduct electricity via cation exchange capacity (CEC), artificially suppressing resistivity and leading Archie equation to overestimate water saturation. Shaly-sand models like Simandoux, Dual-Water, or Waxman-Smits correct for clay conductivity.

How is formation water resistivity Rw determined?

Rw can be obtained directly from laboratory chemical analysis of produced water samples, calculated from the Spontaneous Potential (SP) log deflection, or inferred from water-bearing clean zones (where Sw = 100% and Rw = Rt / F).