Thermodynamics of Microemulsion Systems: Partitioning Relationships, Phase Behavior and Interfacial Tensions
Open Access
- Author:
- Torrealba, Victor Antonio
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 13, 2017
- Committee Members:
- Russell T. Johns, Dissertation Advisor/Co-Advisor
Russell T. Johns, Committee Chair/Co-Chair
Hamid Emami-Meybodi, Committee Member
Zuleima T Karpyn, Committee Member
Themistoklis Matsoukas, Outside Member - Keywords:
- Surfactant
Enhanced Oil Recovery
Microemulsion Phase Behavior
Partitioning Coefficients
Interfacial Tensions - Abstract:
- Surfactant-based enhanced oil recovery is a promising technique in the petroleum industry due to surfactant’s ability to mobilize previously trapped oil by reducing capillary forces at the pore-scale. However, the field-scale implementation of these techniques has been challenging by the high cost of chemicals, which makes the margin of error for the deployment of such methods increasingly narrow. Some commonly recognized issues are surfactant adsorption, surfactant partitioning to the excess phases, surfactant thermal and physical degradation, and scale-representative microemulsion phase behavior. In this dissertation, we present a novel microemulsion phase behavior model accounting for changing micellar curvature conditions under the assumption of a general prolate spheroid geometry. This approach is shown to be consistent with the definition of the three-phase solubilization ratios obtained by combining our previously developed interfacial tension model with Huh’s correlation. This model removes key assumptions in recent microemulsion phase behavior model of Khorsandi and Johns (2016), such as symmetric phase behavior in the Type III region, constant characteristic length- the Type III, constant spherical geometry of micelles, and finite critical characteristic length-scale. Finally, the model is coupled with Huh’s correlation to present a coupled approach that allows for the accurate capturing of both phase behavior and interfacial tensions. For the case considered, the curvature model provided excellent results compared to experimental data. The results of the coupled approach are compared with results consisting of only phase behavior tuning, where the interfacial tensions are described using Huh’s correlation and the standard scaling constant. For the case considered, the curvature model yielded excellent capturing of both phase behavior and interfacial tension data, whereas the alternative approach of just tuning phase behavior yielded unsatisfactory values of interfacial tensions, with discrepancies of over an order of magnitude. Then, we introduce a consistent and robust model that predicts interfacial tensions for all microemulsion Winsor types and overall compositions. The model incorporates film bending arguments and Huh’s equation, and is coupled to phase behavior so that simultaneous tuning of both IFT and phase behavior is possible. The oil-water interfacial tension and characteristic length are shown to be related to each other through the hydrophilic-lipophilic deviation (HLD). The phase behavior is tied to the micelle curvatures, without the need for using net average curvature (NAC). The interfacial tension model is tied to solubilization ratios in order to introduce a coupled interfacial tension-phase behavior model for all phase environments. The approach predicts two- and three-phase interfacial tensions and phase behavior (i.e. tie lines and tie triangles) for changes in composition and HLD input parameters, such as temperature, pressure, surfactant structure parameters, and oil equivalent alkane carbon number. Comparisons to experimental data show excellent fits and predictive capability. Further, we introduce a new empirical phase behavior model based on chemical potentials and . The model is able to describe physical two-phase regions, and is shown to represent accurately experimental data at fixed composition and changing (e.g. a salinity scan) as well as variable composition data at fixed . Further, the model is extended to account for surfactant partitioning into the excess phases. The model is benchmarked against experimental data (considering both pure alkane and crude oil cases), showing excellent fits for a wide variety of experiments, and is compared to the -NAC EoS model for reference. In this research, we allow for surfactant partitioning into both the water and oil excess phases using a simple approach, and then relate the relevant surfactant partitioning coefficients to the state function so that all independent K-values are predicted for all Winsor environments. Surfactant screening based on EO and PO groups is also considered based on estimated K-values. Key dimensionless groups as a function of activity coefficients are identified, which allow for a simplified description of the surfactant partition coefficients. As an example, the surfactant partition coefficients are combined with the CP equation-of-state model to describe and predict the phase behavior when the excess phases are not pure. One common theme in all contributions in this dissertation is the emphasis on having improved predictive capabilities. For every contribution, we propose a way forward for how to determine model parameters using a single or reduced number of experiments, and then predict for conditions outside the range of experimental observation. This is of great importance for petroleum engineering applications.