The synthesis of water-soluble polymers with drag reducing properties

Abstract

The objective of work described in this thesis was to synthesize water soluble polymers with drag reducing properties that would expand the understanding of the relationship between the molecular structure of polymers and drag reduction performance. The additional aim of this study was to identify suitable additives that would enable removal of associating polymers from the low permeability reservoirs. The copolymers of acrylamide and two hydrophobic monomers, n-decyl- and n-octadecyl acrylamide were prepared using micellar polymerisation. Polymers of N-hydroxyethyl acrylamide were also prepared via the same method. Water soluble polymers of styrene and butadiene were acquired by sulfonation of poly(styrene-block-butadiene) with acetyl sulfate. The evidence of the incorporation of hydrophobic monomers, sulfonic acid groups into copolymers and the concentration of hydrophobic moieties was studied using NMR, FT-IR and Elemental Analysis. The influence of the degree of sulfonation on the flexibility of polymers and polymer degradation temperatures were investigated by DSC, DMA and TGA. The associating properties of polymers were studied using Dynamic Light Scattering and rheology. The drag reducing properties were quantified using a standard rheometer equipped with a Couette double-gap measuring geometry, by calculating the percentage of drag reduction (% DR) based on apparent viscosity. The extent of adsorption and desorption of polymers from silica was studied by Total Organic Carbon. From the obtained results it was clear that the associating properties of polymers synthesised in this thesis were dependent on the concentration of hydrophobic moieties. In addition, the formation of hydrophobic associations and the polymer coil dimensions were found to greatly influence the drag reducing properties and shear resistance of copolymers. It was found that hydrophobically modified polyacrylamide promoted higher drag reduction in comparison to unmodified polyacrylamide. In addition, introduction of a small amount of hydrophobic moieties was found to impart drag reducing properties in poly(N-hydroxyethyl acrylamide). Moreover, water soluble sulfonated poly(styrene-block-butadiene) showed high drag reduction efficiency at extremely low molecular weights below the required lower molecular weight limit necessary to produce excellent drag reduction effect. Furthermore, the sulfonation of poly(styrene-block-butadiene) resulted in the reduced thermal stability of polymers and an increase in the degree of sulfonation resulted in the decrease in the flexibility of polymer chains. The extent of adsorption of polymers of acrylamide on silica was found to increase with molecular weight of polymers and was higher for hydrophobically modified polyacrylamide due to the formation of intermolecular associations between copolymer chains. The desorption capability of copolymers with the aid of Cyclodextrin was demonstrated and was found to depend on the type of Cyclodextrin used and on the concentration of hydrophobic moieties. Nearly 100 % of the adsorbed polymer was recovered when even small concentrations of β-Cyclodextrin were applied. Additionally, partial desorption of polyacrylamide with the aid of α and β-Cyclodextrin was also achieved.