Dynamic Adsorption of CO2 Soluble Amine Surfactants for Foam Assisted Carbon Storage: An Industry-First Quantification Under Reservoir Conditions

Abstract

Abstract The success of foam-assisted CO2 enhanced oil recovery and carbon sequestration processes is largely determined by the adsorption level of surfactants in the field. However, the dynamic adsorption behavior of CO2 soluble surfactants, predominately the amine surfactants, remains a challenge due to their unique solubility in brine under most of the reservoir conditions. The reliability of static surfactant adsorption tests is questionable, especially for switchable amine surfactants, because the testing conditions greatly deviate from the reservoir conditions. For the first time in the oil and gas industry, dynamic adsorption tests of switchable amine surfactants were conducted by injecting a proper amount of CO2 with the surfactant solution at reservoir conditions, where CO2 would be completely solubilized. The dynamic adsorption tests were conducted on dolomite at reservoir conditions, where the effluents were collected every 0.05 PV for high-performance liquid chromatography and pH analyses. It is found that the pH of the CO2-saturated brine and the charge of the mineral surface are heavily dependent on CO2 pressure, which can therefore affect the surfactant adsorption behavior on minerals. The desired co-injected volume of CO2 under specific reservoir conditions can be predicted by the Peng-Robinson equation of states model and the iPhreeqc geochemistry module. The pressure gradient during the dynamic adsorption test is almost equal to brine injection at the same flow rate, indicating that all the injected CO2 could be essentially solubilized into the aqueous phase. By using this approach, the pH, salinity, brine compositions (including the potential determining ions), surface charge, and mineral wettability can be largely preserved, being capable of reproducing all the essential geochemistry reactions at reservoir conditions during CO2 injection. The pH of effluent indicates that CO2 has been dissolved in brine and good pH control necessary for surfactant solubility has been attained in the core. From the dynamic adsorption tests, the adsorption of amine surfactants on dolomite is small (0.089 mg/g) in the presence of high-pressure CO2, while the static adsorption tests may significantly overestimate the adsorption levels (0.350-0.510 mg/g). It is also found that the static adsorption tests may overestimate the adsorption levels. Foam-assisted carbon storage using CO2-soluble surfactants has recently attracted great interest in the oil and gas industry. This study provides a robust approach for estimating the adsorption of switchable amine surfactants with good reproducibility, which is more accurate than the existing method of static adsorption. This novel approach is of great importance for decision-makers to quantify the economic feasibility of the foam-assisted CO2 storage process.