The tuning of the electrolyte content in water reinjected during the water flooding process has shown to contribute greatly to increase oil and gas recovery. This is directly related to the fact that different salts and conditions affect differently the electrical double layer formed on the mineral walls of the hydrocarbon reservoirs. Even though there has been a large number of experimental investigations on this topic, the understanding of the phenomena involved in water flooding at the molecular level still needs improvement. Here, we have used molecular dynamics simulations to describe at the atomistic level the formation of the electrical double layer close to the walls of a calcite mesopore. Aqueous electrolyte solutions that are representative of systems observed in the oil and gas industry are considered. Furthermore, the effect of confinement on the ionic conductivity is investigated. The insights obtained are expected to contribute to the specification of the properties of the water being reinjected during water flooding processes, aiming at a higher oil recovery depending on the characteristics of the reservoir. (C) 2019 Elsevier B.V. All rights reserved.