Title: Asphaltenes: materials considerations from the micro- to the macro-scale

Author (Invited): Sara Hashmi, Yale University

Abstract:

Asphaltenes, the most aromatic and largest molecular weight component of petroleum fluids, present challenges in industrial settings due to their propensity to precipitate out of solution and deposit in wellbores and pipelines. This precipitation can occur with depressurization from reservoir conditions, or upon the mixing of different petroleum fluids. Due to the heterogeneity of their chemical structures, asphaltenes have an operational definition only: they are soluble in aromatics, but insoluble in medium-chain alkanes. In the lab, we generate asphaltenes by introducing a precipitant, heptane. Using a combination of light-scattering, rheology, and lab-scale pipe flow measurements, we investigate the precipitation process under a variety of conditions. Our results indicate that the molecular association of asphaltenes is followed rapidly by growth to the colloidal scale, aggregation, and ultimately deposition. Adding dispersants with appropriate molecular structures can halt the process at the colloidal scale to create stable suspensions. Other dispersants can prevent precipitation entirely by molecular association and solvation, but generally require higher doses to be effective. As petroleum reserves with low asphaltene content become depleted, the use of effective low-dosage dispersants or inhibitors becomes a necessary component of industrial operations. While a few potential candidates have been identified in the literature through experiments and numerical simulations, many unanswered questions remain.