1. n. [Formation Evaluation]

A method for desaturating a core sample by placing one end in capillary contact with a porous plate and applying gas or oil under pressure to the remaining surfaces. The liquid in the original fully saturated sample is expelled through the porous plate. At different pressure stages, the sample is weighed to determine the loss of liquid, and the gas or oil pressure increased. Desaturation continues until no more weight loss is observed, at which time the sample is at irreducible water saturation. Core samples are desaturated to measure, for example, capillary pressure, irreducible water saturation, resistivity index or nuclear magnetic resonance response.

See: centrifuge,  nuclear magnetic resonance,  resistivity index