The role of asphaltenes on water/ crude oil emulsion stability

Abstract

Emulsions are colloidal dispersions of two immiscible liquids in which one phase isdispersed into another by shear forces and/or turbulences. In oilfields, water and oil arecoproduced and flow along the lifting lines from the well to the topside unities, being subjectedto continuous changes in pressure and temperature. These parameters may affect thephysicochemical properties of the crude, such as the gas-liquid equilibrium, density, viscosityand, as a consequence, the aggregation state of asphaltenes.Asphaltenes, one of the indigenous amphiphilic components of crude oils responsiblefor w/o emulsion stabilization, may be found in crudes as a molecule or a colloidal aggregate.Pressure and temperature play an important role on the asphaltene aggregation process and mustbe considered in emulsion stability studies (SJÖBLOM; HEMMINGSEN; KALLEVIK, 2007).There is still no consensus about what asphaltene form is able, or more efficient, in stabilizingcrude oil emulsions, maybe because the asphaltenes identity changes from crude to crude(VELAYATI and NOURI, 2021). This may be the reason why demulsifiers must be formulatedfor each specific oil/ water system and their efficiency in breaking up emulsions differs amongdifferent wells (HONSE, et al., 2012).Considering the importance of pressure and temperature on the asphaltene state incrudes, the efficiency of demulsifiers is expected to be strongly dependent on these parametersand the effectiveness obtained from bench tests with dead oils are, in general, notrepresentatives of the oilfield (SJÖBLOM; HEMMINGSEN; KALLEVIK, 2007).In this proposal, all the studies will be performed under PVT controlled conditions,simulating the conditions that the whole system (oil and produced water) are subjected inreservoir and, also, along the lifting lines. It will be studied how the P and T conditions canaffect the stability of W/O emulsions. The methodology to produce and study emulsions withlive systems is not still well defined in the literature. In this work, the emulsions are planned tobe produced by recombining the crude and water with the gas phase. So, the mixture will betransferred back and forth between two free piston cylinders, through a porous plug installed inthe pipe connecting both cylinders. Afterwards, the emulsion produced will be transferred to ahigh-pressure cell with a visualization window. The emulsion phase separation will bemonitored by using a CCD camera. The studies will be performed with four crude oil samples:two heavy and two light (pre-salt). (AU)