An environmentally friendly and low-cost alginate-based gel for water management in petroleum reservoirs: Characterization and efficacy investigation

Water production in petroleum reservoirs poses considerable challenges, such as lower production efficiency, higher operational costs, and severe environmental risks. This study investigates the effectiveness of a novel, sustainable, and economical alginate-based gel system derived from Persian Gulf brown algae in decreasing reservoir rock water permeability. The ultrasonic-assisted method retrieved the most alginate, yielding 56 % at a pH, alginate-to-water ratio, sonication time, and ultrasound power of 11, 10 g/L , 45 min , and 75 W , respectively. The FTIR spectrum showed that the alginate structure had O-H, C-H, C=C, and C-O functional groups. Also, TGA results indicate that the extracted alginate is thermally stable. The effects of polymer concentration, cross-linker content, pH, temperature, and solvent salinity on the properties of the natural gel system were investigated. While the gel strength rose with increasing polymer and cross-linker concentrations, the gelation time decreased. Also, increasing the acidity of the system resulted in higher gel viscosity, attributed to stronger molecular binding. Seawater-based gels exhibited greater strength than distilled water gels due to divalent ions (Mg 2+ , Ca 2+ ) in seawater. The sand-pack experiments demonstrated the ability of the polymer-gel system, which included 3 wt% of the alginate polymer and 1 wt% of CaCl 2 , to reduce permeability by 44.7 % . Furthermore, the coreflood experiments conducted on a carbonate reservoir rock demonstrated the feasibility of in-situ gel formation and a 22.7 % reduction in permeability by injecting a 0.5 wt% alginate solution. The results showed that the sustained gel functioned as a blocking agent by significantly diminishing the water permeability.