Dual crosslinked poly(acrylamide-co-N-vinylpyrrolidone) microspheres with re-crosslinking ability for fossil energy recovery

Microspheres have been proposed to be applied in controlling wastewater production for mature oilfields and migrating leakage for gas and nuclear waste storage. However, it remains challenging for stacked microspheres to maintain strong blocking ability in micron-sized small pores or fractures. In this study, a novel microsphere was developed with comprehensive properties including high deformability and long re-crosslinking time upon tunable swelling ratio for the applications. A dual covalent and physical crosslinking strategy was used to develop novel microspheres reinforced by a hydrogen bond (H-bond, between pyrrole ring and amide group) and coordination bond (between chromium acetate (CrAc) and carboxyl group via hydrolysis process). The microspheres were fabricated via radical suspension copolymerization of acrylamide (AM) and N-vinylpyrrolidone (NVP) in the presence of N, N ʹ-methylene-diacrylamide (MBA) with subsequent introduction of CrAc. MBA induced the strong crosslinking through a chemical covalent bond and H-bond triggered the weak crosslinking which was anticipated to prohibit the hydrolysis of the amide group. The H-bond delayed the formation of CrAc coordination bond by delaying the formation of carboxyl groups, resulting in achieving the re-crosslinking of the microspheres. As a result, the microspheres exhibit the tunable initial size (8–165 μm) and swelling ratio (30–630 μm), with controllable network parameters. The microspheres showed high migration ability (can transport through pores with 1/16 size of microsphere itself), and long re-crosslinking time (up to 16.5 days). The re-crosslinked gel demonstrated dual network structure with districted mesh size ζ distribution.