Objective Tahe carbonate reservoir has high formation temperature (above 110 ℃) and high salt mass concentration of formation water (up to 22×10⁴ mg/L, in which calcium and magnesium ions are nearly 2×10⁴ mg/L). In view of the harsh reservoir conditions of high temperature and high salinity in Tahe oilfield, the existing plugging agent has single selectivity and short plugging time, a new type of plugging agent needs to be developed for plugging.

Methods In this study, the glue solution in simulated injection water with low salt content was prepared, using AM-AMPS copolymer as the glue agent, using water-soluble phenolic resin as the crosslinking agent, and adding Nano silica as the stabilizer. The gel forming time and gel strength were measured, and soaked the gel formed at 130 ℃ in simulated water with high salt content after aging for 3 days to investigate its long-term stability. In addition, in order to explore the mechanism of gel stability and dehydration shrinkage, the gel before and after aging in high salt content water was dehydrated step by step and dried for SEM, IR and XPS analysis.

Results It was found that with the same amount of crosslinking agent and polymer, the stability of the gel was increased by increasing the content of nano silica and the dehydration rate was less than 10% in the simulated water with high salt content for 60 days. The degree of dehydration decreased with the increase of mass fraction of crosslinking agent. After the gel was soaked in high salt water, due to the hydrolysis of primary amide and the cross-linking of carboxylate radical generated from primary amide with calcium and magnesium ions in formation water, the gel grid became denser and the storage modulus increased.

Conclusions AM-AMPS40 water-soluble phenolic resin prepared in low salt water can meet the water plugging requirement of Tahe oilfield. The results can provide guidance of the selection of plugging agents for high temperature and high salinity reservoirs.