Equilibria and kinetics are two basic ingredients for the proper understanding of adsorption and desorption processes between surfactants and rocks. The adsorption and desorption of calcium lignosulfonate (CLS), commonly used as a sacrificial agent in surfactant-based EOR processes, has been studied.
Kinetic results showed that adsorption and desorption are both time-dependent, not instant. Both adsorption and desorption were characterized by a biphasic pattern: a fast step followed by a slow step. Apparent adsorption and desorption rate coefficients were determined by a second-order kinetic model. Desorption is a much slower process than adsorption. Desorption is an un-equilibrium process under normal reservoir flow rate conditions.
Equilibrium results show that CLS adsorption and desorption onto limestone can be described well by the Langmuir isotherm over the tested CLS concentration range, and that increasing concentration increases adsorption density. There is significant hysteresis between CLS adsorption and desorption isotherms. Increasing flow rate slightly decreased CLS equilibrium adsorption. Increasing both NaCl and CaCl2 concentrations increased adsorption density; however, CaCl2 had a much greater impact on the adsorption. Increasing pH decreased CLS adsorption onto limestone. The reasons for the effects of the different factors are elucidated in this paper.