Enhanced Sedimentation and Coalescence by Chemicals on Real Crude Oil Systems

Abstract

Water-in-oil emulsions of a crude oil were prepared and destabilized by addition of demulsifiers. The goal of the study was to compare two different techniques used to evaluate demulsification effectiveness and to study the interfacial response of the demulsifiers. The stability of these emulsions was determined in an E Crit cell and low-field NMR, and the interfacial response of the demulsifiers was measured with the oscillating pendant drop method. The E Crit cell measures the electric field required to induce the formation of free water and the NMR monitors the vertical movement of dispersed water droplets. The stability measurements and the interfacial response gave different indications on the demulsifier effectiveness at different demulsifier concentrations. The difference could be attributed to the difference between how the stability is measured or by the effect of the electric field on the demulsifiers. The separation profiles obtained in the NMR illustrated that the demulsifiers increase the sedimentation velocity at increasing demulsifier concentration. The water recovery rates indicated that the demulsifiers had different properties. The interfacial study showed that low concentrations of demulsifiers decrease both the elastic and viscous modulus of waterÀcrude oil interface. At higher dosages both moduli increase. The different trends can be explained by considering the ratio between the total interfacial area and the demulsifier dosage. The demulsifier dosage was kept similar, but the amount of available area varied from the emulsion stability measurements and the interfacial study.

Demulsification techniques of water-in-oil and oil-in-water emulsions in petroleum industry

“…Equally, if an alkaline additive, for instance, increases the hydrophilicity of asphaltenes in a W/O emulsion through ionization effect, lesser amount of an efficient hydrophilic demulsifier for achievement of an optimum formulation in which separation rapidly occurs is required (the relevant mechanism is described in Section 2.11); likewise, demulsifying surfactants with too low molecular weight (MW < 4000) are unable to resolve the W/O emulsion with low dosages (300-400 ppm) regardless of their hydrophilic/lipophilic affinities [45,47,83]. Additionally, separation vessel dimensions may influence the optimal demulsifier dosage, owing to their impact on the contact time between emulsion and separator [95,96], and/or on fluid dynamics. For example, it was evidenced that larger bed height of a coalescing separator improved the oil removal efficiency of an O/W emulsion due to the provision of longer contact/retention time [95].…”

“…The characteristic relaxation time induced by interfacial film drainage upon addition of a demulsifier is measured from peak frequency of the plot of dilatational viscous modulus against low frequency range [15]. Both elastic and viscous moduli of crude oil-water interface pass through a minimum value at certain concentration of an effective demulsifier [96], signifying the optimum demulsifier concentration as enucleated in Section 2.5.7. Viscoelastic properties of crude oil-water interface are drastically improved once an ultra-high-molecular-weight polymer (such as partially hydrolyzed polyacrylamide or its modified products) is added to the aqueous phase in chemical EOR [128].…”

Model molecules mimicking asphaltenes

“…The stability of resulting emulsions is assessed by measuring the free water appearance kinetics (bottle test). Low Field Nuclear Magnetic Resonance (LF-NMR) can also be studied [138][139][140] .…”

Effect of Water Content, Temperature and Average Droplet Size on the Settling Velocity of Water-in-Oil Emulsions

“…Asphaltenes and resins are two solubility classes of crude oil identified as other important factors for the enhanced stability of water-in-crude oil emulsions. The interplay between the asphaltenes and resins forms strong and elastic films at the oilwater interface (Opedal et al, 2011). In the offshore production of petroleum, emulsions are present at different stages of the production and transportation processes.…”