Archie's law

Archie's law is an empirical relation that estimates the electrical resistivity of water-bearing porous rock from its porosity, water saturation, and pore-fluid resistivity.

Formation factor: The ratio of a rock's resistivity when fully water-saturated to the resistivity of the saturating water. It expresses how the rock's pore geometry raises resistivity before partial saturation is considered.
Well logging: The acquisition and interpretation of measurements made in or near a borehole to characterize underground formations. Electrical logs supply the resistivity inputs used to estimate reservoir properties with Archie's law.
Waxman–Smits equation: A shaly-sand resistivity model that accounts for electrical conduction by clay-bound counterions. It extends beyond Archie's law when clay minerals contribute appreciably to conductivity.
Brine: Water containing dissolved salts at concentrations higher than those of fresh water. Dissolved ions make formation water conductive, and its resistivity is a direct law input.
Gustav E. Archie: An American petroleum geologist who formulated the empirical resistivity relations now known as Archie's law. His experimental work established the equations and their use in formation evaluation.
Cementation exponent: An empirical exponent describing how porosity relates to the formation factor in a porous material. It controls the porosity dependence in Archie's law and reflects pore connectivity and geometry.
Water saturation: The fraction of pore volume occupied by water or brine. The law is commonly inverted to estimate this quantity from measured rock resistivity.
Dual-water model: A shaly-sand conductivity model that distinguishes bound water from movable formation water. It handles clay-associated water that Archie's law treats as part of a clean, nonconductive matrix.
Pore fluid: Fluid occupying the void spaces within a porous solid. The law links the electrical properties of pore fluid to those of the surrounding rock.
Petroleum geology: The study of the origin, occurrence, and recovery of petroleum in geological formations. Archie's relation was developed to interpret fluid-bearing rocks in petroleum exploration.

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PetrophysicsRelated: It converts resistivity measurements into estimates of formation water saturation.