Development of a Methodology for the Optimization of Dehydration of Extraheavy-Oil Emulsions

SummaryWith the increasing development of heavy- and extraheavy-oil (EHO) fields, separation operations are becoming increasingly challenging compared to separation for conventional oil fields. For in-situ bitumen, EHOs produced by thermal-process dehydration require solvent addition, injection of a large amount of demulsifier additives, relatively high operating temperature, and long retention times inside the separators. So, in order to respect specifications on crude oil and water quality at lower cost, an optimization of the different parameters involved in the whole process of separation becomes necessary.In the case of EHOs, the presence of polar heavy components, such as asphaltenes, structured as a rigid film at the water/oil inter-face, limits the coalescence phenomena and, consequently, limits the efficiency of separation by gravity or by using conventional electrocoalescence.The paper presents a methodology that permits the optimization of water and oil separation in the case of an in-situ EHO (produced by thermal process). The crude oil was first characterized in terms of rheological behavior and interfacial properties. The dilatational viscoelastic properties of the interface were determined from measurements performed with an oscillating oil-drop tensiometer. Properties of emulsification were also investigated by using a specific device called a dispersion rig that allows the reconstitution of crude-oil emulsions under controlled hydrodynamic conditions. Then, a laboratory procedure based on electrical stability tests (ESTs) was applied to optimize the concentration of demulsifier required for effective water separation. Finally, the optimal electrical parameters were determined in an electrocoalescer device in the presence of the selected concentra-tion of additive. The efficiency of coalescence was measured by following the growth of dispersed water droplets inside the emul-sion using differential scanning calorimetry (DSC).This methodology may be used advantageously as a useful base for further scaleup studies concerning field separation facilities.IntroductionIn-situ EHOs produced by cold or thermal methods (e.g., steam-assisted gravity drainage) tend to form tight and stable emulsions containing oil, water, diluents, and solids. These emulsions have to be treated either by using conventional gravity-based vessels operating at high temperatures with long retention times and huge chemical injection or by using more-advanced technologies, such as electrostatic coalescers (Sams and Zaouk 2000; Noik et al. 2005, 2006; Eow and Ghadiri 2002).For thermal in-situ EHOs, such as the ones in Athabasca, elec-trocoalescence is scarcely used. This paper will present the specific case of one of these EHOs for which a rigorous methodology was applied in the laboratory to optimize water and oil separation by electrocoalescence. First, some chemical and physicochemical properties, such as rheological behavior and interfacial and emulsification properties, were investigated. Then, a laboratory procedure based on ESTs was applied to select an efficient demulsifier and to determine the optimal concentration required for an effective crude dehydration. Finally, emulsions from the extraheavy crude oils were submitted to electrocoalescence experiments at high frequency on a tubular electrocoalescer device developed in the French Institute of Petro-leum (IFP). The efficiency of coalescence determined by DSC allowed for the evaluation of the influence of parameters such as additive concentration, residence time under electrical field, and temperature. Materials and Methods