Atomic Force Spectroscopy Using Colloidal Tips Functionalized with Dried Crude Oil: A Versatile Tool to Investigate Oil-Mineral Interactions

The recovery efficiency of water flooding (water injection in oil reservoirs to recover oil) can be improved by modification of the ionic composition of the brine. This effect is attributed to changes in the physicochemical interactions within in the crude oil brine rock (COBR) system. To systematically modify these interactions, gain predictive capability, and optimize recovery efficiency, further understanding of these systems is required. Our work introduces a new tool to facilitate the study of interactions in such ternary systems. Utilizing atomic force spectroscopy, we developed a custom dried oil-coated probe which directly measures the interactions between crude oil and a mineral substrate in a varying aqueous environment at their natural length scale. In most of the previous studies, COBR interactions were studied by using model systems wherein crude oil was represented by organic acids, for instance, which is a significant simplification of natural systems that may be unwarranted. In this study, we measured the interaction forces between mineral surfaces and actual crude oils. The experiments allow us to systematically test the effect of brine composition on the forces between mineral surfaces and crude oil components in all their complexity under realistic reservoir conditions. Our results illustrate the reproducibility of measurements made using this custom tool by using multiple probes to show salinity-dependent repulsive interactions between the oil coating and a mica substrate. These electrostatic interactions are consistent with trends expected by the Debye Hiickel theory, showing a decrease in repulsive forces as a function of increasing monovalent ion concentration. Adherence to this expected trend provides insight into the COBR interactions in a particular oil reservoir with particular oil, brine, and mineral compositions. Additionally, the presence of electrostatic forces suggests that the dried crude oil coating retains surface charge throughout the drying procedure. Therefore, this tool has the potential to represent or approximate the electrostatic interactions of the original liquid crude oil system during the study of COBR interactions.