Nanoscale Investigation of Surfactant-Enhanced Solubilization of Asphaltenes from Ailicate-Rich Rocks

The main goal of this study was to investigate the impact of two nonionic surfactants on the solubilization of dense nonaqueous phase liquids (DNAPL) found in crude oils, namely, asphaltenes, from silicate-rich rocks with different mineralogy, pore topology, and wettability states (Bentheimer and Arkose). The surfactants consisted of n-dodecyl β-D-maltoside and triton X-100, which displayed similar properties with the exception of their hydrogen-bonding ability. High-resolution microscope imaging, wettability measurements, and spontaneous imbibition tests were conducted to study the performance of these surfactants on DNAPL solubilization. The interactions between asphaltene molecules, surfactants, and a mineral surface with H-bonding ability were further examined at the molecular-level using molecular dynamics simulations. The results revealed that maltoside could restore the wettability of both sandstones to a higher extent than triton because of its high H-bonding ability with the silanol groups of quartz. This behavior was even more pronounced in tight rocks, such as Arkose, resulting in incremental light nonaqueous phase liquids (LNAPL) mobilization from small pores. Early stages of micellar solubilization of DNAPL by maltoside were successfully observed through molecular dynamics simulations. The solubilization was promoted by surfactant self-assembly, leading to the formation of a continuous surfactant channel that interacted with asphaltenes and promoted their desorption from the mineral surface. This phase eventually grew into a thick surfactant shell trapping DNAPL in its core, as suggested by high-resolution transmission electron microscope (HRTEM) micrographs of microemulsions formed by these NAPL/surfactant-in-brine systems.