Development, evaluation and stability mechanism of high-strength gels in high-temperature and high-salinity reservoirs

The high-temperature and high-salinity environment of the reservoir present a challenge for developing high-strength gels. In this study, a combination of acrylamide/2-acrylamido-2-methylpropanesulfonic acid (AM/AMPS) and partially hydrolyzed polyacrylamide (HPAM) was crosslinked with hydroquinone (HQ) and hexamethylenetetramine (HMTA) to prepare high-strength gels suitable for high-temperature and high-salinity reservoirs. The evaluation demonstrated that the gels exhibited exceptional strength, with a storage modulus exceeding 40 Pa. Gels containing more than 0.2 % crosslinker remained stable for over 120 days in brine with a salinity of 22 × 104 mg/L at 130 °C. Core flooding experimental evaluation revealed that the gel exhibited excellent plugging ability in fractures. Mechanisms of gel hardening and long-term stability in high-temperature and high-salinity environments were investigated by rheological testing, cryo-scanning electron microscopy (cryo-SEM) and Fourier transform infrared spectroscopy (FTIR) analysis. Results suggest that chelation between carboxylate groups in the gel and bivalent cations like calcium or magnesium increases mesh density, leading to hardening of the gel; aging also contributes to maintaining its strength while limiting syneresis due to AMPS presence and high mesh density, thus ensuring stability in extreme environments. The findings, although limited to laboratory-scale conditions and subject to potential variations in real time applications, still serve as a proof of concept for guiding the formulation of high-strength gels in reservoirs under extreme conditions.