Anti-Polyelectrolyte and Highly Resilient Nanosphere-Cross-Linked Polyampholyte Hydrogels with Superior Salt-Tolerant Property for Conformance Control in Ultra-High-Salinity Reservoirs

Abstract

Gel treatment is a highly effective technique for conformance control, significantly managing water production and enhancing oil recovery in mature reservoirs. However, the performance of conventional hydrogel systems often deteriorates under harsh conditions such as elevated temperatures and high salinity. To overcome this limitation, we developed a hydrogel with exceptional stretchability and resilience by integrating phenyl nanospheres (PNSs) as nanocross-linkers within polyampholyte chains. The PNSs were synthesized through precipitation polymerization of divinylbenzene in a water/ethanol solvent. P(AM-AMP-DAD)_PNS gels were fabricated by copolymerizing acrylamide (AM) with equimolar amounts of 2-acrylamido-2-methylpropanesulfonate sodium (AMPS-Na) and diallyl dimethylammonium chloride (DADMAC), utilizing PNSs as cross-linkers. This unique structure achieved a remarkable breaking elongation of 920% at 100 kPa and exhibited no fractures after five cycles at 400% strain. Hydrophobic interactions among PNSs created dynamic association domains, enabling reversible energy dissipation and improving mechanical robustness. The antipolyelectrolyte effect of the polyampholyte chains provided exceptional fracture resistance in ultrahigh-salinity environments. The swelling ratio of P(AM-AMP-DAD)_PNS gels remained stable and even slightly increased in formation water, particularly at 130 °C, where it was 1.2 times higher than at room temperature. Furthermore, this hydrogel demonstrated long-term stability under extreme conditions (130 °C, 2.2 × 10⁵ mg L^–1 salinity, Ca²⁺ + Mg²⁺ = 1.3 × 10⁴ mg·L^–1) for up to 60 days. Core-flooding tests revealed that the fractured core, treated with P(AM-AMP-DAD)_PNS particles and subjected to high-temperature aging, achieved a breakthrough pressure exceeding 6 MPa, with a plugging efficiency of 99.93%. These results confirm the hydrogel’s superior plugging performance under ultraharsh reservoir conditions, making it a promising candidate for enhanced oil recovery applications.