(134g) Miming Acid Oil Component Interactions with Carbonate Reservoirs: A First Principles View on Low Salinity Recovery Mechanisms

Enhanced oil recovery by low salinity water (LSW) injection in carbonate reservoirs constitutes one of the main interests for petroleum industry.  Lately, a molecular mechanism involving acid oil components and the replacement of surface Ca atom by Mg atom has been proposed.  In this work, we studied the thermodynamic feasibility of this mechanism by the calculation of the propionic acid adsorption upon calcite (10-14) and Mg-calcite(10-14) surfaces, in the last one a Mg atom replace a Ca surface atom. We employed first-principles calculations based on Density Functional Theory, in vacuum and in solvent. For the last case we used a continuum solvent model implemented in the Car Parinello approach. In vacuum, we observed that the propionic acid adsorption energy upon both surfaces is negative, not in favor of the proposed mechanism. As a first approach to describe the reactivity in solvent, we include a water monolayer (ML) and we observe a decrease on the adsorption energy due to a change on the surface oxygen atom involved in the acid-surface hydrogen bond, but the acid remains stable upon both surfaces. Additionally, we explore the effect of adding an aqueous media on the adsorption energy. We employ the continuum solvent model and we obtain substantial changes on the energy adsorption due to the increasing of the acid-surface hydrogen bond. In addition, and in order to account for explicit interactions, we add an explicit water ML to this scheme finding a minor energy variation. In both scenarios the acid becomes unstable upon Mg while remains stable upon Ca, in favor of the proposed mechanism. Furthermore, the effect of salinity, temperature and pressure are explored in an effective way through the variation of the solvent dielectric constant (50-90). It can be inferred from our results that if Ca-Mg replacement occurs, this mechanism is thermodynamically feasible for the whole dielectric constant range studied.