Novel CO2-Modified Surfactant for CO2 Sequestration and Crude Oil Viscosity Reduction

Abstract A CO2-modified non-ionic surfactant alkyl polyglycoside (APG) was synthesized for consuming CO2 to reduce carbon footprint and improving the performance of the APG surfactant. Commercially available APG was used as a raw material and reacted with CO2 in a solvent mixture containing dimethyl sulfoxide (DMSO) and a superbase 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) to prepare CO2-modified APG (CO2-APG) under mild synthesis conditions including a low temperature (50-60°C) and a low pressure (2-3 bar). The reaction was not reversible under external stimuli such as temperature and inert gas. The CO2 modification was confirmed by FTIR and UV-vis spectroscopy, suggesting a successful approach to capture CO2 and to reduce CO2 emission. The application of CO2-APG as a viscosity reducer agent (VRA) for heavy crude oil was investigated. CO2-APG exhibited excellent compatibility in a high-salinity water (HSW) at 50°C. The emulsions prepared by mixing CO2-APG solution at 0.2 wt% and heavy oil at an oil-to-water ratio of 7:3 showed a significant decrease in viscosity comparing the initial heavy oil sample at various temperatures. The efficiency of viscosity reduction increased from 70% to 87% with the temperature increased from 40°C to 60°C. The heavy oil displacement efficiency by chemical flooding using CO2-APG injection was also studied via a visualized micromodel approach. The porous structure of the micromodel was designed based on a nature carbonate core. After heavy oil saturation, continuous injection of the HSW for 2.0 PV, CO2-APG solution for 1.0 PV, and the HSW again resulted in a heavy oil production of 15%, 55%, and 3%, respectively. Therefore, a cumulative production of 63% was obtained. This work is of significance in two aspects – first, it provides a novel attempt to incorporate CO2 into APG molecules for potential CO2 sequestration; second, it might be used to improve the performance or broaden the application area of the APG surfactant, such as for heavy oil viscosity reduction and oil displacement.