Salt-induced dual network gel-strengthened foam for gas channeling control in fractured-cavity carbonate reservoirs

Gas flooding is crucial for enhanced oil recovery (EOR) in carbonate fractured-cavity reservoirs, but severe gas channeling reduces displacement efficiency. While foams can mitigate channeling via the Jamin effect, conventional and gel-strengthened foams often suffer from poor stability under high temperature, high salinity, and formation water dilution. This study presents a salt-induced dual network gel-strengthened foam (SDG-Foam) with improved gas-blocking performance and long-term stability. The SDG-Foam comprises a Ca 2+ -induced ion crosslinked network and a high temperature-initiated covalent crosslinked network. The optimized formulation includes sodium alginate (0.5–0.7 wt%), acrylamide (6.0 wt%), crosslinking agent (0.3 wt%), and initiator (0.004–0.006 wt%). Sodium alginate reacts with Ca 2+ in the formation brine to form the first crosslinked network, which can protect foam and gelant solution from being diluted by formation water. At high reservoir temperature, the monomer, crosslinking agent, and initiator eventually gelled, generating a second crosslinked network that prevented foam rupture and greatly increased foam stability. The half-life of SDG-Foam exceeded 18 days under high-temperature (130 °C) and salinity (220,000 mg/L) conditions. The fracture-cavity carbonate plate displacement experiment showed that the SDG-Foam achieved a strong gas channeling plugging, expanded the gas-swept volume, and improved the oil recovery by 11.5%. Visualization tests further revealed that SDG-Foam preferentially migrates to high-permeability channels, effectively sealing gas pathways and improving oil displacement efficiency.