(534f) Asphaltene Adsorption from Toluene Onto Silica through Thin Water Layers | AIChE

(534f) Asphaltene Adsorption from Toluene Onto Silica through Thin Water Layers


Radke, C. - Presenter, University of California-Berkeley
Hu, J., Xi'an Jiaotong University
Asphaltenes in crude oil play a pivotal role in reservoir oil production because they control rock-surface wettability. Upon crude-oil invasion into a brine-filled reservoir trap, rock adherence of sticky asphaltene agglomerates formed at the crude oil/brine interface can change the initially water-wet porous medium into mixed-oil wetting. Mixed wetting changes the flow paths and consequently the oil recovery from reservoirs. However, if thick, stable water films coat the rock surfaces, asphaltenic-oil adhesion is thought to be prevented and the reservoir remains water wet. To our knowledge, no direct evidence is available confirming that water films protect solid surfaces from asphaltene deposition.

Here, we investigate whether water films influence the uptake of asphaltenes dissolved in oil onto silica surfaces. Water films are formed at a silica surface in a quartz crystal microbalance with dissipation (QCMD) by injecting toluene into a QCMD cell initially filled with water. Wetting properties of the silica surface allow water-film formation following Bretherton-type displacement. Film thickness is determined by hydrodynamic theory applied to the QCMD frequency and dissipation signals. Once a water film of known thickness is formed, pure toluene is replaced by asphaltene-laced toluene and the QCMD-adsorbed mass is ascertained from Sauerbrey theory.

We confirm that thick water films prevent asphaltene molecular contact with the silica surface blocking asphaltene adhesion. The thicker the water film, the smaller is the amount of asphaltene deposited. Film thickness necessary for complete blockage onto silica is greater than about 500 nm, well beyond the range of molecular-chain contact. Water films of thickness less than about 500 nm, sandwiched between toluene and solid silica, rupture into thick water pockets and interposed molecularly thin water layers that permit asphaltene adherence. This film-rupture process mimics what happens during reservoir maturation.