The Utility of HLD/NAC to Guide Surfactant Selection and Design

Summary A surfactant/oil/water microemulsion is a complex system. The phase behavior of such systems is extremely complex to accurately capture and properly describe. The Hydrophilic-Lipophilic Difference and Net-Average Curvature (HLD/NAC) model has been suggested to offer the necessary understanding for the design of surfactant formulations and injection slugs. In general, for any model to be of value in design and optimization, it needs to offer a reasonable degree of uniqueness. Therefore, in this work, we use an in-house HLD/NAC model to investigate the utility and power of HLD/NAC EOS to guide the screening and design of surfactants for EOR applications. We investigate the utility of the model from a uniqueness standpoint. In the in-house simulator, three surfactant parameters (surfactant head-area, length and molecular weight) are used to model the phase behavior as a function of brine salinity. Those parameters are generated by fitting the HLD/NAC solubilization predictions to inputted observations. With that single and multi-variate sensitivity analyses were performed. The sensitivity results suggest the non-uniqueness of the three surfactant characteristics. Accordingly, and at least in its current form of implementation, the HLD/NAC model doesn't seem capable of guiding the selection, design and/or optimization of surfactant formulations for EOR applications.