Shear and electrical property measurements of water-in-oil emulsions and implications for multiphase flow meters

We prepared water-in-oil emulsions by blending a synthetic brine representative of the formation water from a production well with dead oil samples from the same well. The composition of the oil was thoroughly characterized using an extended saturates−aromatics−resins−asphaltenes analysis, high-temperature gas chromatography, and two-dimensional gas chromatography with time-of-flight mass spectrometry. The relative dielectric permittivities of the emulsions (10−50% water volume fraction) were measured at 1 kHz using a coaxial capacitor and between 0.2 and 13.5 GHz using dielectric relaxation spectroscopy. The dielectric permittivity is one of the properties used by some multiphase flow meters to determine water volume fractions in production systems. The water volume fractions calculated from the measured oil, water, and emulsion permittivities using the Bruggeman equation were systematically above the measured water fraction by an average of 10% and a maximum of 20%. In contrast, one of Hanai’s equations systematically underpredicts the water fraction by an average of 6%, with a maximum of 12%. Importantly, the permittivities measured using a capacitor changed by 14% over 15 min before reaching its steady-state value. This result has significant implications on the required residence time of fluids in capacitance-based multiphase flow meters. The emulsion permittivities exhibited significant dispersion at frequencies between 0.2 and 1 GHz, a result of importance to multiphase flow meters operating at microwave frequencies. We also measured the shear properties of the emulsion samples and compared them to standard models for estimating emulsion viscosities. The results of the shear experiments have implications for total mass flow rates estimated from multiphase flow meters using differential pressure measurements