Surfactant Behavior Analysis in Enhanced Oil Recovery Blends Using One-Dimensional Proton Nuclear Magnetic Resonance

摘要

In this work, nuclear magnetic resonance (NMR) spectroscopy is used to investigate surfactant phase behavior relevant to chemical enhanced oil recovery. The effect of the solution electrical conductivity on the NMR signals was corrected using reference spectra of known conductivity. This allowed us to develop a semi-quantitative method to estimate the surfactant concentration by correlating it with either integrated NMR peaks or intensity of selected surfactant signal peaks. A distinct change in the slope of the assumed linear relationship between signal intensity and surfactant concentration was observed as the surfactant concentrations were increased. This was attributed to the progressive surfactant aggregation in solution. This result can be used as an alternative method to estimate the critical micelle concentration (CMC) of surfactants. NMR spectra were collected for individual surfactants and their combinations in a variety of saline aqueous solutions. Our results were compared to estimates obtained through more traditional ultravioletvisible (UVvis) spectroscopy and surface tension measurements. Consistency between NMR and surface tension estimates was found. CMC values determined through UVvis were similar, although not quite the same as those of the other two techniques. Similarly, the NMR signals were used to estimate surfactant adsorption in the rock in the so-called static adsorption experiments, in which ground rock is exposed to a surfactant solution of known initial concentration. The results obtained show that NMR offers a powerful alternative to more frequently used methods to estimate not only CMC but also surfactant adsorption, particularly when multiple surfactants are present in aqueous solution.