UC Berkeley

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. If thick, stable water films coat the rock surfaces, however, asphaltenic-oil adhesion is thought to be prevented. We investigate whether water films influence the uptake of asphaltenes in crude oil onto silica surfaces. Water films of known thickness are formed at a silica surface in a quartz crystal microbalance with dissipation and contacted by toluene-solubilized asphaltene. 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 500 nm, sandwiched between toluene and solid silica, apparently rupture into thick water pockets and interposed molecularly thin water layers that permit asphaltene adherence.