Emulsification of Heavy Oil in Aqueous Solutions of Poly(vinyl alcohol): A Method for Reducing Apparent Viscosity of Production Fluids

摘要

Driven by the need to enhance heavy oil production, we have investigated the emulsification properties of poly(vinyl alcohol)s (PVAs) to generate oil-in-water (O/W) emulsions and achieve a significant viscosity reduction. O/W emulsions were successfully prepared using Canadian heavy oil with an American Petroleum Institute (API) gravity of 12° and a water cut of 25%. The effects of PVA molecular weight and degree of hydrolysis as well as emulsifier concentration and mixing method' on emulsion stability and water quality were studied. For this purpose, phase separation kinetics was monitored by means of the Turbiscan Lab Expert particle dispersion analyzer, and the results were then correlated with interfacial tension, wettability, and droplet size measurements. For PVAs having comparable molecular weight, less hydrolyzed samples proved to induce more stable emulsions; this is in agreement with reduced particle size resulting from the increased reduction in interfacial tension. On the other hand, for a similar degree of hydrolysis, the increase of the molecular weight improved emulsion stability. These results, together with the measured droplet sizes and contact angles, indicated that a favorable adsorption of higher molecular weight PVAs at the oil-water interfaces occurs, thereby enhancing steric repulsions between oil droplets. Water quality showed a complex dependency upon the particle size, and the method of mixing was also demonstrated to be critical for emulsion stability. Of the PVAs tested, the PVA with the highest molecular weight (146 kg/mol) and lowest degree of hydrolysis (87%) was found to be the most effective.