Bitumen liberation and flotation using CO2-responsive surfactant and low-salinity brines for oil sands processing

Abstract

Oil sands as a fossil energy remains considerably a promising petroleum reserves to fuel the world’s energy need, though current production has to be aligned with issue on climate change. With determination to concurrently utilize carbon dioxide (CO2), one of the greenhouse gases, into oil sands processing, this thesis focuses on bitumen extraction process (consisting of liberation and aeration stages) using CO2-responsive surfactant (monoethanolamine – lauric acid) with co-presence of low-salinity brines that have been proven as a promising fluid for petroleum recovery. Influences of interfacial phenomena at the bitumen-water-solid system (i.e., the bitumen-water interfacial tension and three-phase contact angle) on bitumen liberation were observed and found to be greatly controlled by fluid chemistry. Individually, surfactant reduced the interfacial tension and enhanced electrostatic repulsion at the bitumen-water interface which hence promoted bitumen liberation, while optimal brine rather constructed the hydration forces to change wettability (the contact angle). When the two chemicals combined at the most optimal proportion (6 mM MEA-LA + 10 mM NaCl), co-contribution from the hydration forces and electrostatic repulsion existed between the bitumen-water and substrate-water interfaces, bitumen liberation was hence greatly improved with much-reduced bitumen-substate contact area attained. Considering the aeration stage, as an alternative to air, CO2 gas is bubbling into the extraction system to attach onto bitumen in order to increase its ability to ‘float up’ and collected. Dissolved CO2 in the aqueous solution restored the interfacial tension back to high value (0.9 mN/m to 16.8 mN/m) due to decreased pH (of which carbonic acid). This partly led to improved bitumen-gas attachability due to such a relatively higher interfacial tension. Furthermore, using CO2 gas instead of ambient air also improved the attachability due to its strongly hydrophobic nature, and this was evidenced by the increased bitumen-gas-water apparent contact angle (i.e., CO2 prefers to wet the bitumen). This observation suggests a promising CO2 utilization as an alternative flotation gas carrier for bitumen aeration. The findings in the current study provide a fundamental guidance on bitumen extraction process enhanced by both surfactant and brine fluids. The current findings confirm a holistic improvement for the whole extraction process with CO2 utilization toward a cleaner production that couples both climate action and affordable energy sustainable goals.