Formation Factor and Water Saturation

  • Lee M. Etnyre


Almost all water saturation calculations using well log data are based on equations that make use of ratios of resistivities. The resistivity of a rock determines its resistance to the flow of electrical current. The flow of electrical current is essentially through the water in the rock’s pore system. Oil and gas as well as solid rock do not conduct electrical current and have nearly infinite resistance. They could be termed insulators. If oil or gas replaces some of the water in the pore system, the rock’s resistance to the flow of current should increase in comparison with a rock of the same porosity having only water in the pore system. The ratio of these resistivities between water-saturated and hydrocarbon-saturated rocks follows a well-established relationship. Thus, by making resistivity measurements, the water saturation of a rock can be established.


Formation Factor Formation Water Water Saturation Pore System Resistivity Index 
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© Springer Science+Business Media New York 1989

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  • Lee M. Etnyre

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