Adsorption Study of Extended Carboxylate Surfactants for High Temperature Carbonate Reservoir Enhanced Oil Recovery
Authors: Wilson Daniel , Morgan Carla , Nguyen Thu , Nguyen Nhut 
Published: March 2022

Abstract
It is estimated that over 50% of the world's oil reserves are tied up in carbonate reservoirs. Predominantly, these reservoirs are oil wet in nature and as such, make sufficient primary and secondary recovery complex. Chemicals are considered as one of the more effective enhanced oil recovery (EOR) sources, but are often complicated by temperature and salinity parameters. Extended carboxylate surfactants have been proven to be effective molecules to positively interact with crude oil at higher reservoir extremes.
In this study, adsorption of alkyl ether carboxylate extended surfactants were evaluated at elevated temperature and constant salinity using a limestone adsorbent media. Static adsorption is a commonly accepted laboratory technique used to help evaluate both technical and economic viability of surfactant based flooding applications in EOR processes. Various reports in literature suggest increases in salinity and temperature may increase adsorption tendencies. Focus was placed here on how various extensions of propylene oxide (PO) and/or ethylene oxide (EO) may influence carboxylate surfactant adsorption data. Results are intended to reveal how augmentations in hydrophilic-lipophilic balance (HLB) may either positively or negatively affect surfactant loss using static adsorption at elevated temperature.
Several different alkyl ether carboxylate surfactants were studied. The academic focus for this effort was placed more on surfactant parameters being evaluated, with regard to carbonate rock mineralogy at high temperature, to study surfactant adsorption behaviour without interference of other influences. The number of mechanisms involved in surfactant loss from aqueous solutions to assorted porous media adds to the overall complexity of this phenomenon. Experimental results found in this study show that various surfactant extensions affect adsorption differently. An increase in some hydrophobic properties appear to increase surfactant adsorption. This was observed through a couple different mechanisms including increasing percent ratio of PO to EO, or increasing molecular weight of the surfactants. Conversely, increasing carbon chain length and increasing degree of alcohol branching appeared to show a general decrease in adsorption trend versus limestone mineralogy, as well as higher percent of EO. It was also observed that ratios of PO and EO extensions will also have a variable influence on surfactant adsorption.
Defining experiments in the laboratory can improve overall economic efficiency of surfactant based chemical EOR processes in the field, which often struggle due to loss of chemicals by adsorption to the reservoir rock.
Surfactant properties provide information on the type and mechanism of interactions involving surfactant molecules at the solid/liquid interface and their efficiency as surface-active agents. Findings from this study will be used to improve understanding on how the role of various extensions on carboxylate surfactants affect surfactant adsorption. This will help lead to enhancements in designing surfactant molecular structures that in turn, minimize adsorption to carbonate rock surfaces, while maintaining desired fluid performance for effective oil recovery.