Water is invariably produced with crude oil. If there is enough shear force when crude oil and produced water flow through the production path, stable emulsions may be formed. This scenario may particularly be present during the production of heavy oils where steam is used to reduce the viscosity of heavy oil or in cases where submersible pumps are used to artificially lift the produced fluids. To efficiently design and operate heavy oil production systems, knowledge of the realistic viscosities of the emulsified heavy oil under the actual production conditions is necessary. This study is an attempt to investigate the effect of water content, pressure and temperature i.e. operating conditions on the viscosity of live heavy oil emulsions.
Two heavy oil samples from South America were used for this study. The stock tank oil (STO) samples were recombined with the corresponding flash gases to reconstitute the original reservoir oil compositions. Live oil-water emulsions were prepared in a concentric cylinder shear cell using synthetic formation water, under predetermined pressure, temperature, and shear conditions. The stability of live emulsions was investigated using a fully visual PVT cell, while viscosities were measured using a pre-calibrated high-pressure capillary viscometer. Viscosities were measured at least in three different flow rates at the testing conditions. In addition to live oil emulsion studies, the stability and droplet size distribution of STO emulsions were also determined.
Experimental results indicated that the inversion point for the stock tank oil emulsions was approximately 60 % water cut (volume) and that the average droplet size was increasing with water content. For all measured cases, viscosities varied with temperature according to an Arrhenius relation while viscosities did not indicate any variation with flow rate (shear) within the range of tested flow rates. Measured viscosities also increased as pressure decreased below the bubble point of the sample as lighter hydrocarbon components evolved. The measured viscosities increased as much as 500% due to the presence of emulsions before sharp drop in viscosity beyond the inversion point. The variation of viscosity with water content for live emulsion samples indicated that the inversion point for live emulsions is similar to that of stock tank oil samples.