(456a) The CO2-Solubility and Viscosity Enhancing Potential of CO2-Philes Functionalized With Aromatic Groups

The low viscosity of CO₂ at typical enhanced oil recovery (EOR) conditions is responsible for a poor mobility ratio that causes viscous fingering and poor sweep efficiency, leading to reduced efficiency and yield. To overcome this problem, there is a need to develop CO₂-soluble additives that will increase the effective viscosity of CO₂ without the use of a co-solvent. The only known polymeric direct thickener poly(fluoroacrylate-co-styrene) (polyFAST) has been shown to significantly increase the viscosity measured by falling cylinder viscometry and Berea sandstone core mobility experiments. The proposed mechanism of aggregation responsible for this viscosity enhancement is believed to be π-π stacking between aromatic rings. However, high molecular weight polymers like polyFAST require significant amounts of expensive fluorinated moieties in order to impart solubility. In addition to their cost, fluorinated compounds have undesirable environmental impacts.

Therefore, this work focuses on the development of less expensive and safer hydrocarbon-based CO₂ thickeners.  Because our prior studies have demonstrated that unacceptably high pressures are required to dissolve non-fluorous polymers, this study entails the use of small, associating compounds to create a thermodynamic illusion of a polymer. Each CO₂ thickening candidate consists of at least one non-fluorous CO₂-philic segments and at least two slightly CO₂-phobic functionalities that promote intermolecular aggregation (e.g. aromatic groups).  Solubilities of a range of newly synthesized molecules in CO₂ and their associated viscosity enhancing abilities will be presented.  Preliminary results indicate that it is possible to design such novel CO₂-thickening candidates that are up to 1wt% soluble in CO₂ at pressures commensurate with EOR.