Salinity of the Water and Water-Cut Measurement

From the early 1950s, it has been shown and known that measurements in the oil-in-water emulsion phase are made difficult by the high conductivity of the salt water. In this phase, the oil droplets appear as voids in the conductive water and therefore, the nature of the oil does not affect the measurement. Any change in the salinity makes a large difference in the conductivity. This conductivity in parallel with the measuring capacitance of standard capacitance probes prevents an effective measurement from being performed. Although some probes claim to work on attenuation of the signal, the water is so conductive that the measurement is very minimal at best. A good measurement must include the effects of the salt.

In a paper by Mr. Robert S. Wood, Capacitance-type b.s. and w. recorder features automatic, continuous operation, The Oil & Gas Jorurnal, Dec. 8, 1958, says that when the water continuous phase is entered, the "resistance of the emulsion has dropped so low that the probe is practically short-circuited." He gives the resistance (one divided by the conductivity) for various salinity waters versus water-cut. It is obvious where the water continuous phase begins. Other literature gives the equations for the conductivity vs. salt and percent water.

Another paper which gives the response for salt in water is by A. Stogryn and is titled Equations for Calculating the Dielectric Constant of Saline Water, IEEE-MTT, August, 1971. Again, it is obvious that the parameters of measurement are all dependent upon both temperature and salinity to a high degree. Salinity and temperature MUST be considered and corrected in the measurement for accuracy and reproducibility.