Abstract
During the Steam Assisted Gravity Drainage (SAGD) production process, complex water-in-oil-in-water (W/O/W) emulsions are generated, which need to be treated to promote water-phase separation and recovery of the oil. Due to the similar density of heavy oil and water, dilution is frequently required to improve the separation process, but also to reduce the viscosity of the extracted bitumen to facilitate flow. Although significant research has been carried out to understand the stabilizing and destabilizing factors of both water-in-oil and oil-in-water emulsions, studies related to the characterization of complex W/O/W emulsions containing diluents are still limited. When carrying out this type of analysis, the complex relationship among different variables should be considered, such as the chemistry and concentration of stabilizing agents, water-to-oil ratio and droplet charge. Temperature and shearing methods are process conditions that must be also considered.
In this study we combined several techniques to characterize production fluids and synthetic emulsions, using diluents with different composition. Differential Scanning Calorimetry (DSC) was explored as a tool for analyzing the emulsions. Since the oil present in these fluids did not exhibit any thermal transition between -80°C and 30°C, the DSC could be used to quantify the amount of free and emulsified water in one measurement, for either synthetic or produced emulsions. Results demonstrated that this technique has a high potential to characterize emulsified systems with precision, requiring only small amounts of sample and without applying any pre-treatment. The technique can also be used to screen demulsifiers after performing a specific thermal treatment within the equipment.
Bottle tests are commonly used in the industry to monitor emulsion behavior. They are easy to perform, but are subject to the judgment of the experimenter, who measures the partitioning of the phases and in some cases their relative opacity. To perform a more quantitative analysis, demulsification was monitored in real-time, using a multiple light scattering device. Phase separation rates were highly influenced by the nature and amount of diluent used and they were correlated with droplet size, interfacial tension and surface pressure measurements. Results were rationalized based on the differences in the asphaltene-resins interfacial film, which will determine the emulsion behavior upon separation in the field when using demulsifiers.
