The oil recovery potential of acrylamide-based, associative thickening polymers has recently been evaluated in a coreflood study of our department. Associative polymers are anionic, water-soluble copolymers modified with varying degress of pendant hydrophobic groups. By intermolecular interactions of these hydrophobic moieties a fully reversible network of polymer coils can be formed.The oil recovery efficiency of a series of copolymers based on acrylamide, 2-acrylamidopropane sulfonic acid (ATBS) in combination with a hydrophobic comonomer has been determined in linear coreflood experiments at a temperature of 60°C. Synthetic sea water was used as brine and Bentheimer sandstone as core material. The evaluated polymers differed in molecular weight and associative groups' content.While anionic polyacrylamide (APAM) shows very similar resistance factors (RF) in coreflood experiments with and without oil, a significantly reduced RF in the presence of oil has been found for the associative polymers. The magnitude of this decrease in resistance factor was dependent on the specific type of associative polymer.The effect can be ascribed to the weakend intermolecular interaction of the hydrophobic groups in the associative polymers in the presence of oil. Even though the RF value is reduced in the presence of oil, it still remains higher than that of regular APAM.At low flow rates representing reservoir conditions a high resistance factor was observed and oil production was improved. This observation can be explained by an increase of the capillary number caused by the high RF of the polymer drive. A good correlation between oil production and capillary number was established.Permeability reduction effects explained the high mobility reduction observed with the associative polymers, as the bulk viscosity data did not correlate with the in-situ flow properties of the polymers in porous media.

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A new thickener based on associative properties and its application in polymer flooding is discussed. The new thickener is an anionic, water-soluble copolymer containing pendant associative groups. These associative groups are based on a novel chemistry (patent application filed). The viscosity of the new copolymer shows superior behavior compared to existing technologies like partially hydrolyzed polyacrylamide (PHPA), especially at elevated temperature and in presence of salt respectively divalent ions. A viscosity of 33 mPas at 60°C could be obtained by adding 900 ppm of the new copolymer to synthetic sea water. In comparison, with a high molecular weight standard partially hydrolyzed polyacrylamide (PHPA) a value of only 3 mPas was reached. Moreover, the new polymer shows good resistance to shear during injection. Core flood experiments were run to prove that the new associative thickening polymer is applicable in the field. These data show injectivity into a 2 Darcy core. Moreover the apparent viscosity of the polymer flood in the core outperforms the values found with commonly used polymers by far. The residual resistance factor indicates low adsorption onto sandstone.

The relative positions and conformations of the prosthetic group FAD and the cofactor NADH have been remarkably conserved within the structurally diverse group of flavin enzymes. To provide a chemical rational for such an obviously optimal relative disposition of the redox partners for efficient reaction we have synthesized NADH models with Zn(II)-cyclen substituents for reversible flavin binding in water. Altogether, four of these model systems with systematically varying spacer length between the recognition site and the redox active dihydronicotinamide were prepared. The binding of these model systems to riboflavin tetraacetate was confirmed by potentiometric pH titration in water and their reaction with flavin was followed by UV-vis spectroscopy in aqueous media under physiological conditions. The measurements reveal a significant rate enhancement of up to 175 times that of an intermolecular reaction. Moreover, a strong dependence of the reaction rate on the spacer length was observed, which clearly shows that within the dynamic reversible assembly only the optimal relative disposition of the redox partners ensures an efficient redox reaction.

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