Summary
With 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 interface, 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 concentration of additive. The efficiency of coalescence was measured by following the growth of dispersed water droplets inside the emulsion using differential scanning calorimetry (DSC).
This methodology may be used advantageously as a useful base for further scaleup studies concerning field separation facilities.
Evaluation of a sulfanilic acid based surfactant in crude oil demulsification: an experimental study