Effect of Diluents and Asphaltenes on Interfacial Properties and Steam-Assisted Gravity Drainage Emulsion Stability: Interfacial Rheology and Wettability

Abstract

In steam-assisted gravity drainage (SAGD) operations, the produced fluids are complex water-in-oil-in-water (W/O/W) emulsions. A diluent is often added to reduce the density and viscosity of the heavy crude oil. However, the quality and composition of the diluents may in some cases increase emulsion stability and cause the dehydration of the oil to be more difficult because there are more surface-active agents added to the oil coming from the diluent streams. Thus, this work was aimed at studying the effect of three different diluents on interfacial film formation of a Canadian heavy oil. Interfacial elasticity and compressibility were evaluated, and the results were then correlated with emulsion stability. The wettability of the systems was also studied. The systems studied behaved as if a bidimensional gel near its gelation point had organized at the interface, in which adsorbed amphiphilic materials, such as asphaltenes and resins, self-aggregated at the interface, forming a network that acts as a stabilizing mechanism for produced emulsions. When the interface was aged, its gel strength was much higher than the fresh interface, suggesting an explanation as to why aged emulsions are more difficult to treat. Unlike elasticity and interfacial tension measurements, it was demonstrated that compressibility measurements can predict emulsion stability under different conditions. The higher the crumpling film ratio and the lower the compressibility, the more stable the emulsion. This test method gives more insights into the mechanisms of emulsion stabilization caused by diluents and asphaltenes and can potentially be employed to study the structure and demulsifying performance relationships of emulsion breakers (EBs) and reverse emulsion breakers (REBs).

Interfacial Rheology of Heavy Oil-Aqueous Systems at Elevated Temperatures and Pressures: Effect of Diluents

“…In a previous work we demonstrated that the interfacial oscillating drop tensiometer technique can be used to correlate the interfacial rheology of a diluted oil drop against brine with SAGD emulsion stability (Nguyen et al, 2014). Compressibility measurements showed that the aged interface between diluted oil and water behaves like a bidimensional gel near its gelation point, in agreement with other authors (Dicharry et al, 2006;Bouriat et al, 2004).…”

“…Theses values are lower than values of around 18 mN/m reported by other authors for Athabasca bitumens (Isaacs and Smolek, 1983). Since the brine used for this work has a very low salt concentration, most of the reduction is expected to be due to the presence of surface-active species in the diluents as has been reported previously (Nguyen et al 2014, Balsamo et al, 2013. The effect of temperature and pressure on crude oil interfacial tension is still not well understood.…”

“…Heavy oil was isolated from the raw emulsions for interfacial tension measurements, following a procedure described previously (Balsamo et al, 2013). SARA analyses of the heavy oil led to the results reported in Table 1. Three diluents (D, F, P), currently employed at different Canadian locations for SAGD operations, were used to dilute the dry oils (1:1 ratio).…”

“…All curves exhibit a slope change that indicates the presence of an irreversible film at the interface (Nguyen et al, 2013). Phases I and II correspond to high and low compressibility regions, respectively (Yarranton et al, 2007;Aske and Sjöblom, 2002;Sztukowski et al, 2003).…”

“…(a) As samples are aged, all curves are shifted to higher area normality values, showing an increase of the phase transition and crumpling points (see Table 3). This is due to an increased elasticity of the interfacial film (Nguyen et al, 2013) because adsorbed asphaltenes and perhaps other surface-active agents have the tendency to reorganize themselves at the crude oil/water interface. Indeed, this is the reason why a fresh emulsion will not be stabilized by interfacial elasticity to the same extent as an aged emulsion.…”