Experimental Evaluation of a Recrosslinkable CO2-Resistant Micro-Sized Preformed Particle Gel for CO2 Sweep Efficiency Improvement in Reservoirs with Super-K Channels

Abstract

A recrosslinkable CO2-resistant branched preformed particle gel (CO2-BRPPG) was developed for controlling CO2 injection conformance, particularly in reservoirs with super-permeable channels. Previous work focused on a millimeter-sized CO2-BRPPG in open fractures, but its performance in high-permeability channels with pore throat networks remained unexplored. This study used a sandpack model to evaluate a micro-sized CO2-BRPPG under varying conditions of salinity, gel concentration, and pH. At ambient conditions, the equilibrium swelling ratio (ESR) of the gel reached 76 times its original size. This ratio decreased with increasing salinity but remained stable at low pH values, demonstrating the gel’s resilience in acidic environments. Rheological tests revealed shear-thinning behavior, with gel strength improving as salinity increased (the storage modulus rose from 113 Pa in 1% NaCl to 145 Pa in 10% NaCl). Injectivity tests showed that lower gel concentrations reduced the injection pressure, offering flexibility in deep injection treatments. Gels with higher swelling ratios had lower injection pressures due to increased strength and reduced deformability. The gel maintained stable plugging performance during two water-alternating-CO2 cycles, but a decline was observed in the third cycle. It also demonstrated a high CO2 breakthrough pressure of 177 psi in high salinity conditions (10% NaCl). The permeability reduction for water and CO2 was influenced by gel concentration and salinity, with higher salinity increasing the permeability reduction and higher gel concentrations decreasing it. These findings underscore the effectiveness of the CO2-BRPPG in improving CO2 sweep efficiency and managing CO2 sequestration in reservoirs with high permeability.