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Oilfield Glossary
Oilfield Glossary
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clay-bound water

Formation fluids
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1. n. [Formation Evaluation]
Water within the clay lattice or near the surface within the electrical double layer. This water does not move when fluid is flowed through the rock. In the normal definition used by a log analyst, clay-bound water is not part of the effective porosity and is the difference between total porosity and effective porosity. Clay-bound water is understood to include the interlayer water, although the contribution of the latter to the electrical properties of the clay may be different from the water in the electrical double layer. In the dual-water and the Hill-Shirley-Klein models, the volume of clay-bound water is related to the cation-exchange capacity per unit volume, Qv, by expressions that depend on the salinity and temperature of the electrolyte in which the clay is immersed. Direct measurement of the clay-bound water volume in the laboratory is difficult.