Adaptation Mechanism of Sodium Methallyl Sulfonate (SMAS) Modified Gel for Deep Profile Control in Middle and Late Waterflooding Reservoirs

In the middle and late stage of water flooding, reservoirs are featured with developed high-permeability channels, severe heterogeneity, high temperature and high salinity. Conventional gel systems are prone to dehydration, shrinkage, structural degradation and near-wellbore plugging, failing to reach deep formation.

Compared with conventional gels, the gel system prepared with Sodium Methallyl Sulfonate (SMAS) shows prominent advantages for in‑depth profile control:

1. Excellent salt and calcium‑magnesium resistance
   The strongly hydrophilic sulfonate groups form a dense hydration film, effectively resisting ion compression in high‑salinity formation water. The gel network maintains complete structure without dehydration or shrinkage under complex water quality.
2. High temperature and long-term thermal stability
   The methyl branched chains bring significant steric hindrance, which inhibits thermal hydrolysis and oxidative degradation of polymer chains. The cross‑linked network remains stable under long-term reservoir high-temperature conditions and delays gel breaking.
3. Good deep injection and migration performance
   SMAS modified copolymer has moderate molecular rigidity and flexible branched structure. It possesses low initial viscosity and superior injectivity, smoothly migrating along dominant flow channels to realize deep reservoir placement.
4. Selective plugging & effective flow diversion
   It forms a controllable and uniform cross‑linked structure with moderate plugging strength. It preferentially seals thief zones and high-permeability layers without blocking low-permeability oil layers, realizing effective deep fluid diversion and improving swept volume.
5. Low adsorption loss & strong reservoir adaptabilityThe negatively charged sulfonate groups reduce excessive rock surface adsorption. The system adapts to wide pH and harsh formation environments, maintaining long-term plugging performance and lasting profile control effect.

Core Conclusion

With outstanding salt tolerance, thermal stability, deep migration ability and selective plugging performance, Sodium Methallyl Sulfonate (SMAS)-based gel systems perfectly meet the technical demands of deep in‑depth profile control for mature waterflooding oil reservoirs.