Generation of Complex Emulsions During the Application of Improved Recovery Methods in Venezuelan Heavy and Extra-Heavy Oil Reservoirs: A Critical Review

Abstract

Abstract The formation of emulsions during the production of highly viscous crude oils is one of the biggest issues observed both in cold production and after the application of IOR methods in Venezuelan heavy and extraheavy oil reservoirs, with impact on the lifting of crude oils, separation of phases, fouling, production costs, etc. For the cold production case, the presence of water with strong compositional and salinity variation, coupled with the presence of gas in the case of foamy oil, could generate very stable oil-water and gas-oil emulsions; hence complicating the phenomena after the application of thermal or chemical IOR methods. This article presents a review of: 1) different types of emulsions found in cold production as well as thermal and chemical IOR methods, 2) factors that affect the stability of the emulsions (compositions of crude oil and formation and injection waters, type of injection fluid, temperature, etc.), 3) fluid characterization methods (gravimetric method, droplet size distribution, centrifugation, rheology, etc.), 4) recommended demulsifiers based on laboratory, and field experiences in Venezuela and internationally. These criteria will be reviewed in detail, establishing the main insights associated with the emulsion formation, providing related conclusions and perspectives for treatment and prevention measures. Based on the results of this review, it can be highlighted that the presence of resins and asphaltenes in the crude oil has a fundamental role in the stability of the emulsions found during cold production in the Orinoco Oil Belt and that the composition of the formation water might increase the stability of the emulsions (Mg2+ and Ca2+). The application of thermal as well as diluent injection methods generates emulsions that involve precipitation of asphaltenes, which together with sand production in the process, leads to making phase separation processes more complex. Furthermore, the application of chemical methods could cause phase trapping (for the surfactant case) with impact on chemical losses, and water- in-oil emulsion with high viscosity after the addition of alkali in lab experiments. A worldwide review of field and laboratory remediation methods indicates that possible emulsion treatments include the use of silica nanoparticles, polyglycerol fumarate ester, heavy aromatic naphtha, electrical heaters, among others. This article presents the main insights related to the generation of emulsions in Venezuela and for developing strategies for emulsions breakers adapted to each IOR process. It also covers the effect of water chemistry, oil composition and type of IOR/EOR process on the characteristics of emulsion and emulsion stability, and consequently the impact on the technical and economic criteria of the process.