Micromechanical Cohesive Force Measurements between Precipitated Asphaltene Solids and Cyclopentane Hydrates

Asphaltenes are the heaviest and most polar class of compounds in crude oil, which may precipitate out of solution due to changes in the pressure, composition, or temperature. During production, aggregation between asphaltene solids may lead to viscosification of the oil phase and/or deposition of the solids on the flowline wall. This study presents the first measurement of asphaltene interparticle cohesive forces using a micromechanical force (MMF) apparatus, which is similar to that used previously to investigate gas hydrate interparticle cohesion. Asphaltene solids were precipitated from two crude oils, and cohesive force measurements were performed for particle pairs with diameters ranging from 100 to 200 mu m. In air, the measured cohesive forces between the asphaltene particles were approximately one-half of those measured between hydrate particles in cyclopentane-saturated nitrogen vapor. Asphaltene cohesive force was measured in liquid cyclopentane, to provide a comparison against cyclopentane hydrate; in the liquid phase, the asphaltene cohesive forces were 1 order of magnitude smaller than the cohesive forces between cyclopentane hydrates. In addition, the hydrate asphaltene adhesive force in liquid cyclopentane was measured to be of the same order of magnitude as that of hydrate particle cohesion; this result suggests the potential for asphaltene-hydrate solid aggregation as a potential flow assurance risk in oil and gas production flowlines.