Polyelectrolyte Complex Induced Stimuli-responsive Self-association and Reinforcement of Interpenetrated Poly(acrylamide-co-vinyl acetate)/alginate Particles for Fossil Energy Recovery

Abstract Stimuli-responsive poly(acrylamide-co-vinyl acetate)/alginate-based hydrogel particle (AIPNG particle) are obtained by free-radical polymerization of acrylamide monomer and vinyl acetate monomer which interpenetrates with branched polyethyleneimine (B-PEI)/alginate-based polyelectrolyte complex (PEC). The AIPNG particle is developed for reservoir conformance control in Ca-rich reservoirs. The AIPNG particle can swell 13 to 25 times its initial volume, and the equilibrium swelling ratio is dependent on brine type and concentration. The swelling and elastic modulus of the AIPNG particles are strongly influenced by salt in the aqueous solution. The release rate of B-PEI from B-PEI/alginate PEC structure, combining with the swelling ratio, the environmental temperature, and Ca2+ concentration, determines the self-association time and rheological strength of the AIPNG gel. Preparation pH influences the protonation degree of B-PEI and subsequently affects the self-association behavior by delaying the intermolecular transamidation reaction between poly(AM-co-VA) acrylamide pendant groups and PEI nitrogens. With the component adjustments, the self-association starting time can be controlled between 2 to 16 h depending on temperature and swelling ratio. Ca2+, supported from environmental brine, can influence the self-association time and help reinforce the re-formed bulk gel by forming Ca-alginate bonds and creating a hard Ca-shell on the gel surface. Field trial results in Zhidan oilfield demonstrated the potential of AIPNG particle products in high-salinity/middle-temperature reservoirs which provided a new way for maintaining the oil production and reducing water-cut in the mature oilfields.