Equilibria and kinetics are two basic ingredients to properly understand an adsorption and desorption process 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 by dynamic depletion experiments.
Kinetics results show 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 one-site second-order kinetic model. Desorption is a much slower process than adsorption. Desorption is an un-equilibrium process under normal reservoir flow rate condition.
Equilibrium results show that CLS adsorption and desorption onto limestone can well be described by Langmiur isotherm in our tested CLS concentration range, and increasing concentration increase adsorption density. CLS adsorption and desorption are hysteresis. Increasing flow rate slightly decreased CLS equilibrium adsorption. Increasing NaCl and CaCl2 concentrations both increases adsorption density; however, CaCl2 has a much greater impact on the adsorption. Increasing pH decreased CLS adsorption onto limestone. The reasons for different factors effect were elucidated.