In attempting to separate the oil from the three-phase production stream, the addition of emulsion breakers changes the IFT and promotes the agglomeration of small droplets into larger ones that separate quickly. Indeed, certain corrosion inhibitors added to the three-phase production stream can lower the produced water IFT enough (<1 to 5 dyne/cm) to cause the droplet size of the entrained oil to be small enough that no injection well plugging is observed, even at high oil carryover (percent levels) in the reinjected produced water. Most chemicals added during the course of drilling or production have a major effect on the IFT of the produced water and the hydrocarbons. Also, the IFT determines the ease of separation of oil from water, because it determines the size of the oil or water droplets, depending on which phase is internal. IFT is an important factor in enhanced recovery. At very low values of IFT, oil and water become miscible and behave as a single phase. The lower the IFT, the smaller the droplet of the internal phase. If the phase boundary separates a liquid and a gas or a liquid and a solid, the attractive force at the boundary usually is called surface tension however, the attractive force at the interface between two liquids is called interfacial tension (IFT). Surface tension (interfacial tension or IFT) is a measure of the attractive force acting at a boundary between two phases. When resistivity of formation water is used in electric-log interpretation, the value is adjusted to formation temperature.

Formation water resistivity, R wg, is expressed in units of Ω-m. The direct measurement method is essentially the electrical resistance through a l-m 2 cross-sectional area of 1 m 3 of formation water. It can be measured directly or calculated. The resistivity of formation water is a measure of the resistance offered by the water to electrical current.

Water viscosity centipoise