Bridging the gap between drop coalescence and interfacial rheology

Flow assurance describes the economical and technically feasible transfer of crude oil from the reservoir to the processing plant or point of sale. The transfer is complicated by the numerous surface active agents native in crude oil that readily deposit at the solid-liquid and liquid-liquid interfaces. Such unwanted deposition can lead to costly production shutdowns.

In this presentation focus is given to the detrimental impact of asphaltenes. Asphaltenes are the heavy and most polar components of crude oil, readily partitioning at the liquid-liquid interface to form an interfacial barrier that hinders drop-drop coalescence.[1] Using interfacial rheology techniques and an in-house built Integrated Thin Film Drainage Apparatus we are able to relate the interfacial film mechanical properties to the drop coalescence time.[2] In the viscous dominant regime droplets coalesce with relative ease, while the droplets remain stable when the shear response is elastically dominant. This transition is a time-dependent property unlike the dilatational rheology component which always exhibits elastic dominance from short aging times. The mechanism for droplet stability is attributed to the high shear yield stress of the asphaltene film.

Demulsifiers are added to the continuous phase to enhance droplet coalescence.[3] A biodegradable, amphiphilic molecule (ethylcellulose) was used to study the demulsification process. Demulsifier molecules compete for available interfacial area and displace the adsorbed asphaltenes. Since the asphaltenes are strongly irreversibly adsorbed, their displacement results in the formation of large asphaltene aggregates and voids in the interfacial film.[4] Such behaviour is characterised by a diminishing shear elastic contribution, thus providing favourable conditions for drop coalescence.[5]

Overall, the research is applying a range of highly sophisticated experimental techniques to better understand the interfacial layer properties and competitive interaction between multiple surface active species.

[1] Rane et al., Langmuir, 28 (26), 9986-9995, 2012 [2] Harbottle et al., Langmuir, 30 (23), 6730-6738, 2014 [3] Pensini et al., Energy and Fuels, 28 (11), 6760-6771, 2014 [4] Natarajan et al., Submitted to Energy and Fuels [5] Liang et al., To be submitted