Self-Assembly Systems Based on Betaine-Type Hydrophobic Association Polymer Used in Acid Stimulation: Effects of Surfactant and Salt Ion

Abstract

Hydrophobic association polymers containing various functional groups have a great deal of application potential as a self-thickening agent in carbonate acidification, while the improvement of their viscosification ability under high temperature conditions remains a significant challenge. A kind of betaine-type hydrophobic association polymer (PASD) intended for use as an acid thickener was synthesized through aqueous solution polymerization with sulfobetaine and a soluble hydrophobic monomer. The structure of PASD was characterized by FT-IR and ¹H NMR. It is found that during the acid-rock reaction, the physical cross-linking between PASD and cationic surfactants (STAC) occurs through noncovalent bonding forces such as micellar interaction and electrostatic interaction, forming a self-assembly acid. The optimum conditions for the construction of the self-assembly acid and its viscosification properties, rheological properties, temperature, and salt resistance were evaluated by a six-speed rotating viscometer and a HAAK MARSIII rheometer. The results suggest that the main source of the viscosity rise of the self-assembly acid is the CaCl₂ produced during the acid-rock reaction. As the acid-rock reaction progresses, the hydrodynamic radius of the self-assembly acid increases, and tighter aggregation structures form. The viscosity of the self-assembly spent acid still keeps in 140 mPa·s under 140 °C shearing for 1 h at 170 s^–1, which indicates that the self-assembly acid has excellent viscosification ability and temperature resistance. Compared to PASD acid, the self-assembly acid can be used at a wider range of temperatures, and its research and development have given rise to novel ideas for the use of HAWPs as an acid thickener.