Magnetic polyacrylamide-based gel with tunable structure and properties and its significance in conformance control of oil reservoirs

The polyacrylamide-based gel used for oilfield conformance control exhibits poor temperature and salt resistance. This paper proposes the use of inorganic-organic core-shell materials as chemical crosslinkers for the polyacrylamide-polyethyleneimine (PAM-PEI) gel system to regulate and design its gel structure, enabling it to withstand harsh reservoir conditions. To achieve this, Fe 3 O 4 @PEI nanoparticles were prepared using a facile one-pot method and employed as chemical crosslinkers for the PAM-PEI gel. Herein, the Fe 3 O 4 "core" provides strong stability derived from the inorganic material, and the PEI "shell" reacts with the PAM molecular chain in a transamidation reaction, so that the Fe 3 O 4 @PEI nanoparticles are riveted inside the gel by chemical crosslinking, which greatly enhances the gel structure. The Fe 3 O 4 @PEI nanoparticles exhibit a nearly spherical shape with an average diameter of approximately 75.6 nm and demonstrate excellent dispersion in water, possessing a zeta potential of 40.8 mV. In comparison to the control PAM-PEI gel, the PAM-PEI-Fe 3 O 4 @PEI gel exhibited significantly enhanced gel strength, rheological properties, long-term thermal stability, and anti-salt properties. It demonstrated a tan(δ) value of 0.12, indicative of its behavior as a nearly robust gel. Even after 360 days of placement at 90 °C in a 20 g/L NaCl solution, the gel maintained its Sydansk code at code I . Moreover, NaCl was observed to act as a retarder for this gel, while its Sydansk strength remained unaffected. In addition, the PAM-PEI-Fe 3 O 4 @PEI gel is magnetically responsive, so it can be utilized with a magnet generator to enhance its plugging performance and control its directional movement. By monitoring the magnetization rate of the gel in the reservoir, high permeability layers can be accurately identified, thus providing important practical applications in reservoir management.