CARBON DIOXIDE THICKENING AGENTS FOR REDUCED CO2 MOBILITY

The objective of this work is to design, synthesize, and evaluate direct carbon dioxide thickeners. The thickener must dissolve in CO2 without the introduction of a cosolvent. The thickener, in dilute solution of less than one weight percent, should be capable of at least doubling the viscosity of dense CO2 at temperature and pressure conditions characteristic of CO2 EOR floods.A bulk-polymerized, random copolymer of fluoroacrylate (71mol%) and styrene (29mol%), Mn=540,000, has been identified as an efficient CO2 thickener using falling cylinder viscometry and flow-through-porous-media viscometry. For example, a 0.5wt% solute of the random copolymer in CO2 tripled the viscosity of liquid CO2 flowing through a 100md sandstone core at superficial velocities of 1~10ft/day.Non-fluorous polymers are also investigated in an attempt to identify a less expensive, more environmentally benign thickener. Our first step is to identify a highly CO2-philic, hydrocarbon-based polymer. Among all commodity polymers, poly vinyl acetate, PVAc, is identified as the most CO2 soluble, non-fluorous, hydrocarbon-based commercial available polymer. Nonetheless, PVAc does not exhibit sufficient solubility in CO2 at reservoir conditions to form the basis of a class of CO2 thickeners