Nonquilibrium and Equilibrium Stationary States of Zwitterionic Surfactant Dynamic Adsorption on Limestone Cores at Oil-Reservoir Conditions

Dynamic adsorption of a zwitterionic-type surfactant cocamidopropyl hydroxysultaine on limestone cores at oil reservoir conditions, i.e., under 2000 psi pressure, 130 °C temperature, and in the presence of seawater with 30 800 ppm NaCl, has been studied through core-flood displacement tests and in the absence of oil, at an injection rate of 120 cm3·h–1 up to 60 pore volumes (PV). The amount of adsorbed surfactant has been determined from mass balance by calculating its concentration through high performance liquid chromatography (HPLC). The normalized surfactant concentrations (NSC) have been used in terms of the PV, and then they are obtained the corresponding dynamic adsorption curves. Dynamic adsorption isotherm curves of the zwitterionic surfactant diluted in seawater showed a steep rise between 1 and 3 pore volumes (PV), and the saturation conditions were kept up to 60 PV. An average surfactant adsorption of 0.1138 ± 0.0126 mg·g–1 was determined. Quantum theoretical studies show that the electronic energy gap of (104) the limestone is electrically neutral, preferably acquiring a negative charge tendency, these results imply that the calcite surface will preferentially interact with positive ions, so that the cations present in the solution interacting in the limestone, resulting in a positive charge in the rock that implies that the surfactant cocamidopropyl hydroxysultaine interacts in the rock by the anionic group.