Geochemical Modeling of the Interplay Between Potential Determining Ions During Brine-Dependent Recovery in Carbonate Rocks

Abstract Brine-dependent oil recovery in carbonate rocks has developed into an active area of research in the past two decades. It is well documented in the literature that wettability of carbonate rocks is altered due to desorption of oil acid groups from rock surfaces by the adsorbed sulfate, while the divalent cations co-adsorbed to maintain the surface charge balance as well as to reverse the oil-surface charge. Though the symbiotic interaction between active ions (Ca2+, Mg2+, and SO42−) and the rock surface has been established but how they systematically interplay at different conditions have not been well explored and available data seems inconsistent. In the present work, we develop a reactive transport model that includes various reaction sets like aqueous reactions, mineral reactions in terms of precipitation and dissolution, and surface sorption reactions in terms of adsorption and ion exchange to investigate and discuss the affinity of these active ions toward the rock surface. The important thermodynamic properties were obtained by using the model to interpret single-phase experiments. The model results were in remarkable agreement with the produced ion histories reported from the single-phase experiments. There were delays observed in the produced active ion concentrations because of retention at the rock surface. For two-phase experiments, the model excellently replicated the produced ion histories and oil recoveries obtained during various brines injections, using the same thermodynamic parameters. Although, the ion transports are impacted by the presence of oil because of reduced surface area accessible to the active ions. The established thermodynamic parameter can be applied to predict various brine-dependent recovery processes in different carbonate lithology as no significant difference was observed for the interplay between active ions and either chalk or limestone rocks.