Development and Application Potential of Dilution-Resistant Gel for Water Control in Deep Fractured-Vuggy Reservoirs

Summary Effective water control in deep fractured-vuggy reservoirs remains a significant challenge due to extreme heterogeneity, high-temperature/high-salinity environments, and severe dilution of injected gelation solution by formation water. Conventional gel often fails under such conditions because dilution inhibits gelation. To address this, a novel dilution-resistant gel (DRG) engineered for deep-source water control by incorporating sodium alginate (0.4–0.6 wt%) was developed. Upon contact with calcium ion (Ca2+)-rich formation water, sodium alginate rapidly forms dense, impermeable interfacial membrane that encapsulates gelation solution, effectively shielding it from dilution and enabling successful gelation even at 1:10 gelation solution-to-formation water volumetric ratio. Laboratory evaluations under reservoir-representative conditions (130°C, 220,000 mg/L) confirmed DRG’s performance. Interfacial rheology measurements revealed stable elastic modulus (G′ = 5.99 Pa) and viscous modulus (G″ = 3.52 Pa), indicating a mechanically resilient barrier capable of withstanding dynamic flow. DRG demonstrated exceptional resistance to both static and dynamic dilution while maintaining excellent viscoelasticity. Microstructural analysis showed a refined, highly interconnected 3D network structure with pore sizes of 10–20 μm significantly denser than conventional gel (15–30 μm)—which enhances water retention and mechanical integrity. Moreover, thermal stability was markedly improved, with temperature limit elevated by 3.9°C (initial state) and 9.3°C (after 60 days of aging) compared with conventional gel. Fracture plugging, parallel fracture, and complex model visualized oil displacement experiments, validating the DRG’s field applicability. In fracture core (1–10 mm), DRG achieved stable plugging pressure gradients of 7.5–11.5 MPa/m under dilution—comparable with undiluted conventional gels. Compared with the primary waterflooding, DRG enhanced oil recovery by 22.34% and increased pressure by 38.04 kPa in the parallel fracture configuration, outperforming the conventional gel (13.07% and 22.12 kPa). In complex fracture and fractured-vuggy configurations, the DRG enabled effective multicycle water diversion, increasing sweep efficiency from 36.83% to 81.99% in fracture networks and from 43.52% to 95.13% in fractured-vuggy configurations. This DRG presents itself as a potential option for deep-source water control in complex deep fractured-vuggy reservoirs, providing an effective strategy to manage water production and enhanced oil recovery (EOR).