(125c) Cohesive Force Measurement Between Precipitated Asphaltene Solids

Asphaltene solids may precipitate in subsea crude oil wellbores and flowlines, due to the rapid decrease in fluid pressure during flow. While the consequence of asphaltene deposition and build-up at the wall is well characterised, little is known about how precipitated asphaltene particles behave in flow. If secondary solids are also present, asphaltene particles with a strong aggregation potential may interact with other solids, such as gas hydrate. In this presentation, we discuss adaptations to a micromechanical force (MMF) apparatus that enable measurement of cohesive force between asphaltene particles, which were precipitated from crude oil diluted by various light aliphatic hydrocarbons and filtered on a 0.45-micron nylon paper. The results demonstrate that asphaltene cohesive forces may be up to twice those measured previously for gas hydrate, with solid-solid cohesion as the primary mechanism. MMF data provides further insight into the asphaltene particle surface free energy. The cohesive force data demonstrate that this free energy is very sensitive to the type of crude oil from which the asphaltenes were extracted, suggesting the potential for MMF-based studies to characterise the inherent activity of the asphaltene species within crude oil. For three different Australian crude oils, further tests were performed after the asphaltene-active binding resins were stripped from the asphaltene surface. The data demonstrates a uniform shift toward higher cohesive force, suggesting that these active resins may function to decrease asphaltene surface free energy.