Effect of asphaltenes on the thermal properties of emulsions encountered in oil recovery operations

Fabrication temperature of crude oil and bitumen emulsions was found to produce a very strong impact on dynamic viscosities η and activation energies of a viscous flow Eact. An anomalous increase of both η and Eact was observed in emulsions, fabricated at 36 °C, while fabrication at 45 °C improved the flow properties. The narrow critical range of thermally-induced anomalies extends from ≈30 to ≈42 °C, as revealed by studies of a matrix crude oil. At room temperature the materials retained a long-term memory of fabrication conditions. We suggest that the anomalous thermal effects are triggered by a structural phase transition in the asphaltene/resin molecular subsystem. Below the wax appearance temperature structurally modified asphaltene particles evidently act as cementing species in extended networks of wax crystals.