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

Abstract

In SAGD (Steam Assisted Gravity Drainage) operations the produced fluids are complex water-in-oilin-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 as there are more surface-active agents added to the oil coming from the diluent streams. To simulate temperature and pressure conditions during SAGD operations, this work studied the effect of three diluents on interfacial rheology of a Canadian heavy oil and synthetic brine at 120°C and 130 psi and then correlated with emulsion stability and oil dehydration. When compared to 25°C, all three diluents exhibited higher higher compressibility at 120°C, while the initial interfacial tension, "phase change" area ratio (area ratio at which the phase change from high compressibility region to low compressibility region), and crumpling ratio (ratio of the compressed surface area to the original area at which the interface starts to collapse) exhibited a more complex behavior. The higher interfacial tension and higher compressibility were correlated with the lower emulsion stability at increasing pressure and temperature in the absence of treating chemicals. Increasing ageing of the film from 10 minutes to 1 hour at 120°C had a similar effect on the three diluents, suggesting the formation of a more elastic film as asphaltenes start to cross-link on the interface. The effect of demulsifiers (emulsion breakers-EB and reverse emulsion breakers-REB) on interfacial was also investigated at RT and 90°C. Demulsifiers that produced the minimum interfacial tension (IFT) with changing concentrations demonstrated to be the best demulsifiers in the bottle tests. A synergistic effect in reducing IFT was found when EB and REB when combined.

Mechanism of High Stability of Water-in-Oil Emulsions at High Temperature

“…According to the density experiment, the density difference between two phases almost remained unchanged as temperature increased, so the high temperature did not make the shape factor of the asphaltene model oil droplet change in the range of measurement. Indeed, the effect of temperature on crude oil interfacial tension is still not well-understood …”

Effect of Emulsion Breakers on Interfacial Tension Behavior of Heavy Oil–Water Systems

“…The temperature plays an important role in the interfacial interactions by influencing the kinetics of the chemical packing at the oil/water interface and the solubility of the EB and natural surfactants in the different phases. The resulting effect of an increasing temperature can been attributed to a balance of the following effects: an increased asphaltene solubility that induces the formation of smaller aggregates that are more surface-active (as a result of the weakening of interaggregates π or hydrogen bonding), a more effective displacement of the asphaltenes at the interface by the EB molecules or by the species resulting from the interaction between EBs and natural surfactants, and an increased partitioning of the EB molecules in the aqueous phase. ,− Pinpointing the dominant mechanism that needs to be addressed for success in the field, however, is very difficult, in part because of the complexities of the entire system. All of the aforementioned mechanisms could play a part in the efficiency of the EB in question and should be considered.…”

“…These conditions were selected to be close to the actual conditions under which the EBs are used at the specific facility where the production fluid was collected. In this facility, the EB is injected in several places topside and no downhole injection takes place. , …”

“…In this facility, the EB is injected in several places topside and no downhole injection takes place. 11,13 Once the oil drop was created, it was then retracted at a constant volume rate (0.2 μL/s). Images were recorded during the drop contraction, and IFT and surface area were measured as fluid was withdrawn from the drop.…”

“…A range of different interfacial measurement techniques have been investigated in previous works. − This past research into the interfacial compressibility and interfacial tension (IFT) of SAGD fluids yielded valuable insights into the mechanisms of destabilization of SAGD emulsions. − In these tests, the term compressibility represents the ratio of surface area/volume of the dispersed droplets suspended in water. Interfacial films that form at the oil–water interface might become irreversible, making the droplets more resistant to coalescence.…”