Patrice Abivin

Rheological Study of Foamy Oils

When depleted, heavy oils can appear as foams with formation of dispersed gas bubbles. This phenomenon can occur during production or oil-gas separation and results in changes in flow properties of the live oil. Our main objective is to understand the influence of these bubbles on heavy oil flow properties and to test different theories: correlations predict either a decrease or an increase in the foamy oil viscosity with the gas volume fraction. Several live heavy oils are depleted inside the pressure cells of controlled stress rheometers to form foamy oils. Viscosity is continuously measured using oscillatory and continuous tests from the nucleation to the disengagement of bubbles from oil. The occurrence of bubbles is checked and visualized with X-ray scanning experiments. This particular experimental approach allows us to successfully study the rheological behavior of foamy oils in relationship with the two main parameters which are the composition and the viscosity of the crude oils. We observe that foamy oil kinetics is mostly related to the oil viscosity and that the presence of bubbles leads to an increase in heavy oil viscosity. However, several tests reveal a strong influence of the shear rate: the higher the shear rate, at a lower level the viscosity is stabilized. These results make us point out the major role of bubble deformation under a shear rate on the viscosity of foamy oils. Finally, a theoretical model describing the viscosity of foamy oil is established. It takes into account both first-order kinetics of appearance and release of bubbles in oil and a basic suspension model. Results from this model are in agreement with experimental data obtained from different heavy crude oils.

Patrice Abivin is doing his PhD in the Université de Bretagne Occidentale and the IFP. He is working with Dr M. Moan, I. Henaut, and J.F. Argillier.