New Formulation of Tertiary Amines for Thermally Stable and Cost-Effective Chemical Additive: Synthesis Procedure and Displacement Tests for High-Temperature Tertiary Recovery in Steam Applications

Abstract A newly formulated chemical additive from a group of amines has been tested and applied to in-situ heavy-oil thermal recovery. Switchable-hydrophilicity chemical additives were successfully synthesized from N,N-dimethylcyclohexylamine in the form of homogeneous and hydrophilic solution. Fundamentally, tertiary amines comprise functional groups of hydrophilic and hydrophobic components. These unique features enable this chemical additive to wet both water and heavy-oil, yielding potential interfacial tension improvement. Furthermore, the reversible chemical reaction of this chemical additive yields both positive and negative ions. An ion pair formed due to the adsorption of cations—[C8H17NH+]—on the surface of heavy-oil, whereas the anions—[HCO3−]—promoted solid phase surface charge modification; therefore, resulting in the repulsive forces between heavy-oil and the rock surface—substantially improving water-wetness and restoring an irreversible wettability alteration due to the phase change phenomenon during steam injection. We have substantiated that the application of these switchable-hydrophilicity tertiary amines (SHTA) could lead to auspicious recovery mechanisms—wettability alteration and interfacial tension reduction—even in extremely high-temperature steam flooding, thus promoting phase distribution improvement in porous media by diminishing the capillary forces and the eventual favorable heavy-oil recovery performance. In this research, heavy-oil acquired from a field in western Alberta encompassing the viscosity of 5,616 cP at 25°C was utilized in each experiment. All experiments were performed and measured at high-pressure-high-temperature steam conditions up to 200 psi and 200°C. To study the interfacial properties, quantitative contact angle and interfacial tension measurements were performed on rock/heavy-oil/hot-water and steam systems using a high-pressure high-temperature IFT cell under different chemical concentrations. On the other hand, dynamic experimental studies in investigating the residual oil behavior in porous media and oil recovery performance were conducted through micromodel visualization and core flood experiments. These micromodels and sandstone cores were initially saturated with synthetic brine water and then displaced by heavy-oil to mimic reservoir saturation history. Subsequently, steam was continuously injected (3 pore volumes) and followed with the injection of SHTA as tertiary recovery. We perceived that favorable interfacial tension reduction was achieved, and irreversible wettability could be auspiciously restored after combining SHTA with steam as a result of the solid-phase surface charge modification to be more negatively-charged. Phase distribution/residual oil in the porous media developed after steam injection was able to be auspiciously convalesced, indicating that capillary forces could be reduced. Consequently, over 80% of the residual oil could be recuperated post-SHTA injection presenting favorable oil recovery performance. In addition to this promising evidence, SHTA could be potentially recovered by switching its reversible chemical reaction to be in hydrophobic form; hence, promoting this chemical additive to be both reusable and more economically effective. Comprehensive studies and analyses on interfacial properties, phase distribution in porous media, and recovery performance exhibit essential points of view in further evaluating the potential of SHTA for tertiary recovery improvement. Valuable substantiations and findings provided by our research present useful information and recommendations for fields with steam injection applications.

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