Enhanced Oil Recovery

This topic deals with the study of Enhanced Oil Recovery (EOR) methods, particularly CO₂ flooding and surfactant flooding processes. Beside extensive phase behavior studies under typical reservoir conditions (1-400 bar and 5-80°C), the structures of these systems are investigated by scattering methods, e.g. SLS, DLS, SAXS and SANS.

CO₂ injection is a technique used for recovering residual oil from mature reservoirs [1]. It gains more and more interest due to the importance of carbon dioxide capturing and sequestration. In most reservoirs, CO₂ is in a supercritical state (scCO₂). The swelling of crude oil by scCO₂, and consequently the efficiency of a flood, strongly depends on the miscibility of crude oil and solvent. Therefore, immiscibility of scCO₂ with crude oil leads to poor recovery, which poses some limitations to CO₂ EOR procedures. Additionally, viscosity or gravity effects could decrease the sweep efficiency and therewith the recovery rate. The miscibility of scCO₂ and crude oil can be improved by solubilizing an appropriate additive in the scCO₂. In this project, the compatibility of different additives with scCO₂ is investigated in order to identify compounds that enable an easy co-injection of the additive within the flow of the CO₂. Therefore, phase behavior studies under typical reservoir pressures and temperatures with a (model) crude oil are performed in a home-made high-pressure cell [2].

Another promising EOR method is the “surfactant flooding” process (Fig. 2), which plays an important role due to the outstanding ability of surfactants to reduce the interfacial tension between oil and water and to improve the wettability of reservoir rocks [3]. In a systematic study, microemulsions containing pure n-alkanes ranging from medium-chain oils (e.g. n-dodecane) to pure long-chain oils (e.g. n-dotriacontane) or even technical-grade waxes (e.g. SASOLWAX 5805) became possible using both pure and technical-grade non-ionic n-alkyl polyglycol ether (C_iE_j)-type surfactants [4]. In an ongoing project, other technical water-based microemulsions are studied to elucidate the effect of pressure, temperature, salt concentration, and the length of n-alkanes on the phase behavior of these systems. The model of Salager [5] is subsequently applied to predict the optimal state of the candidate microemulsion system.

1. Rommerskirchen, R., Bilgili, H., Fischer, J., Sottmann, T.: Impact of Miscibility Enhancing Additives on the Flooding Scheme in CO₂ EOR Processes. In: SPE Improved Oil Recovery Conference. pp. 12-. Society of Petroleum Engineers, Tulsa, Oklahoma, USA (2018).
2. Schwan, M., Kramer, L. G. A., Sottmann, T., Strey, R.: Phase behaviour of propane- and scCO₂-microemulsions and their prominent role for the recently proposed foaming procedure POSME (Principle of Supercritical Microemulsion Expansion). Phys. Chem. Chem. Phys. 12, 6247-6252 (2010). https://doi.org/10.1039/B909764C
3. Bera, A., Mandal, A. J.: Microemulsions: a novel approach to enhanced oil recovery: a review. Petrol. Explor. Prod. Technol. 5, 255-268 (2015). https://doi.org/10.1007/s13202-014-0139-5
4. Schneider, K., Ott, T. M., Schweins, R., Frielinghaus, H., Lade, O., Sottmann, T.: Phase Behavior and Microstructure of Symmetric Nonionic Microemulsions with Long-Chain n-Alkanes and Waxes. Industrial & Engineering Chemistry Research. 58, 2583–2595 (2019). https://doi.org/10.1021/acs.iecr.8b04833 
5. Salager, J.-L., Forgiarini, A. M., Bullón, J.: How to Attain Ultralow Interfacial Tension and Three-Phase Behavior with Surfactant Formulation for Enhanced Oil Recovery: A Review. Part 1. Optimum Formulation for Simple Surfactant–Oil–Water Ternary Systems. J. Surfact. Deterg. 16, 449-472 (2013). https://doi.org/10.1007/s11743-013-1470-4

• Prof. George J. Hirasaki, Department of Chemical and Biomolecular Engineering, Rice University, United States of America