Inexpensive CO2 Thickening Agents for Improved Mobility Control of CO2 Floods

Abstract

The objective of this research was the design, synthesis and evaluation of inexpensive, nonfluorous carbon dioxide thickening agents. We followed the same strategy employed in the design of fluorinated CO 2 polymeric thickeners. First, a highly CO 2 -philic, hydrocarbon-based monomer was to be identified. Polymers or oligomers of this monomer were then synthesized. The second step was to design a CO 2 -thickener based on these CO 2 -philic polymers. Two types of thickeners were considered. The first was a copolymer in which the CO 2 -philic monomer was combined with a small proportion of CO 2 -phobic associating groups that could cause viscosityenhancing intermolecular interactions to occur. The second was a small hydrogen-bonding compound with urea groups in the core to promote intermolecular interactions that would cause the molecules to "stack" in solution while the arms were composed of the CO 2 -philic oligomers. Although we were not able to develop a viable thickener that exhibited high enough CO 2 solubility at EOR MMP conditions to induce a viscosity increase, we made significant progress in our understanding of CO 2 -soluble compounds that can be used in subsequent studies to design CO 2 -soluble thickeners or CO 2 -soluble surfactant-based foaming agents. These findings are detailed in this final report.In summary, we assessed many polymers and verified that the most CO 2 -soluble oxygenated hydrocarbon polymer is poly(vinyl acetate), PVAc. This is primarily due to the presence of both ether and carbonyl oxygens associated with acetate-rich compounds. In addition to polymers, we also made small acetate-rich molecules that were also capable of associating in solution via the inclusion of hydrogen-bonding groups in hopes of forming viscosity-enhancing macromolecules. Despite the presence of multiple acetate groups in these compounds, which can impart incredible CO 2 -solubility to many compounds, our attempts to make acetate-rich high molecular weight polymers and small hydrogen-bonding compounds did not yield a highly CO 2 -soluble polymer or hydrogen-bonding associative thickener. The conclusions of our molecular modeling calculations confirmed that although acetates are indeed "CO 2 -philic", nitrogen-containing amines also interact favorably with CO 2 and should also be examined. Therefore we obtained and synthesized many N-rich (e.g. amine-containing) polymers. Unfortunately, we found that the intermolecular polymer-polymer interactions between the amines were so strong that the polymers were essentially insoluble in CO 2 . For the convenience of the reader, a table of all of the polymers evaluated during this research is provided. Executive SummaryThe objective of this research was the design, synthesis and evaluation of inexpensive, nonfluorous carbon dioxide thickening agents. We followed the same strategy employed in the design of fluorinated CO 2 polymeric thickeners. First, a highly CO 2 -philic, hydrocarbon-based monomer was to be identified. Polymers or oligomers of this monomer wer...