Geochemical Modeling of Engineered Water Injection in Carbonates under Harsh Conditions: New Insights with Ionic Adsorption

Carbonates are characterized by low oil recovery due to their positive surface charge and consequent high affinity to negatively charged crude oil, rendering them to a state of mixed-to-oil wettability. In order to understand the rock/brine/oil interactions and their effect on potential-determining-ions (PDIs) adsorption/desorption during engineered water injection is needed for realistic and representative estimations of oil recovery. Therefore, this study reveals a novel approach to capture various interactions and better predict the effect of PDIs adsorption/desorption as well as concentrations of various ionic species in the effluent using Phreeqc. In this work, we determined adsorption/desorption of PDIs for the first time using surface complexation reactions and then we validated our results with experimental data from the literature. Our results showed that the presence of PDIs and their respective adsorption/desorption results in surface charge decrease and increase in pH. Also, this study found that ionic adsorption depends on ionic strength and species activity where calcium adsorption remained constant while magnesium and sulfate adsorptions varied with ionic strength. Moreover, magnesium ion was found to be the most sensitive ionic species to temperature as opposed to calcium and sulfate ions. In addition, sulfate spiking and dilution decrease the sulfate adsorption since the sulfate starts reacting with magnesium and forming complexes. Additionally, deionized water resulted in the highest charge decrease and pH increase with related incremental oil recovery. The adsorption/desorption of ions is case-dependent and thus, the findings cannot be generalized