CO2-Modified Surfactant for CO2 Sequestration in Carbonate Reservoir

Abstract A CO2-to-chemical method was proposed for CO2 sequestration by injection of the CO2-based chemical solution into carbonate reservoirs. The CO2 modification of a non-ionic alkyl polyglycoside (APG) surfactant was conducted using a glass reaction vessel in a reaction equipment under gentle conditions at a temperature of 50°C and a CO2 pressure of 2 bar. In the presence of 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) and using dimethyl sulfoxide (DMSO) as a solvent, CO2 reacted with the hydroxyl (-OH) groups of the APG structure, especially the -OH group attached on the C6 position of the glucose unit, to transfer the non-ionic -OH group to the anionic -COO- functional group. By this approach, CO2 was successfully incorporated into the APG molecule to yield a CO2-modified APG (CMAPG) product to effectively reduce CO2 gas emission. The CO2 consumption capacity was estimated to around 0.13 ton of CO2 per ton of APG raw product, which is higher than most of the recently developed CO2 absorbers. This CO2-involved reaction was not reversible by external stimuli and the CMAPG surfactant was thermally stable at 50°C, suggesting that CO2 will not be released during sequestration. The new surfactant also demonstrates an enhanced properties in terms of interfacial tension (IFT) reduction and adsorption on carbonate. The IFT between crude oil and CMAPG solution decreased by approximately ten-fold compared with that obtained from the APG solution. Both static and dynamic adsorption of CMAPG onto carbonate are higher than the adsorption of the APG precursor, indicating a significant potential in CO2 sequestration by injecting the CMAPG solution into depleted carbonate reservoirs.