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

Abstract

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, CC, 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 (Mg²⁺, Ca²⁺) 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 CaCl₂, 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.