Use this geological calculation for a transparent first-pass interpretation of measured rock, soil, fluid, well, stratigraphic, isotopic, geophysical, or seismic data under an explicitly selected model.

Rt

True formation resistivity in ohm metres.

Rw

Formation water resistivity in ohm metres.

Porosity

Porosity as a volume fraction.

m

Cementation exponent m.

n

Saturation exponent n.

a

Tortuosity factor a.

Invert the Archie equation for water saturation from true resistivity, formation water resistivity and porosity. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Sw

Water saturation as a volume fraction.

• Log-derived porosity, shale volume, permeability, and saturation depend on tool type, borehole conditions, invasion, lithology, matrix and fluid properties, environmental corrections, calibration, and depth matching. Core and pressure data should constrain interpretation.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Compare independent measurements and models, retain units and analytical metadata, propagate uncertainty, and validate interpretations against logs, cores, maps, laboratory data, or field observations.

• Well Log Rxo Porosity Calculator

  Invert the Archie equation in the flushed zone to estimate porosity from Rxo and mud-filtrate resistivity.

• Well Log Permeability Wyllie Rose Calculator

  Estimate permeability in millidarcies from porosity and irreducible water saturation with the Wyllie-Rose power-law relation.

• Well Log Water Saturation Simandoux Calculator

  Solve the Simandoux shaly-sand equation for water saturation including shale-conductivity correction.