Comparative Performance of Polymer Gel Systems of DIPA/Chromium Acetate for Water Shutoff with Simultaneous CO₂ Sequestration Prospects in Depleted Oil Reservoirs

Viscous polymer gels are important to address water production issues in depleted oil and gas reservoirs. These gels specifically target water movement from highly permeable pores and provide blockage via gelation resulting in cross-linked networks of adequate viscoelasticity. Thus, in this study, two cross-linkers (chromium acetate and diisopropanolamine (DIPA)) were used to develop viscous polyacrylamide (10,000 ppm)-based gels of different gelation/working times, followed by the discussion on comparative water shut-off and CO2 sequestration performance in synthetic porous media enriched with a formation equivalent salinity of 17,000 ppm. The gelation time varied with the concentration of the cross-linker with an inverse relationship between (b/w) cross-linker concentration and gelation time. DIPA-based gels exhibited higher gelation times ranging from 5 to 8 h than the ones of chromium acetate (2–3 h). Flooding experiments also ensured gel placement and its impact on generated pressure and permeability. The pressure jumped to 500–600 psi from 40 psi, while the permeability reduced from 157 to 96 mD for G1-2 and 174 to 87 mD for G2-2. Thus, the permeability reduced by around 50% and 39% after the placement of G1-2 and G2-2 gels, respectively, which makes these gels suitable for water shut-off in porous media. Moreover, the amount of CO2 storage volume increased by ∼70% and ∼45% when G1-2 and G2-2, respectively, were injected. On the other hand, the breakthrough time delayed, and CO2 reached the outlet end after ∼8 h (G1-2) and ∼6.6 h (G2-2) as compared to 4.5 h (the case without gel). Viscosity measurements were conducted before and after gelation, where viscosity after gelation increased and moreover showed the least dependency on thermal gradient than the one before gelation. Some dilution of polymer gel with injected water was confirmed through the viscosity change b/w effluent and water before the flooding test. From the results, it can be stated that gel use for water shut-off tests can make the entire process sustainable by meeting higher oil demands and simultaneous carbon sequestration in viscoelastic cross-linked networks of polymer gel.