Development and Evaluation of Re‐Crosslinkable Calcium Alginate Microspheres for Profile Control in High‐Salinity Reservoirs

ABSTRACT Polymer microspheres have been widely utilized in profile control to mitigate reservoir heterogeneity. Since most conventional polymer microspheres and preformed gel particles have limitations in long‐term plugging of large pores and fractures, this study proposes a novel re‐crosslinkable calcium alginate (CaAlg) polymer microsphere system, which dynamically enhances the plugging performance by embedding glycerol triglycidyl ether (GTE). The microsphere triggers a ring‐opening addition reaction between GTE and polyethyleneimine (PEI) in the PEI solution, rapidly forming an integral gel, which significantly enhances both plugging strength and longevity of large pores and fractures. Re‐crosslinking time can be controlled by adjusting the injection timing of PEI to achieve dynamic optimization of plugging. Effects of temperature, PEI concentration, and salinity on microsphere re‐crosslinking behavior and gel mechanical properties were experimentally investigated. Size distribution, chemical structure, and micro‐morphology of the microspheres are characterized by laser particle size analyzer, infrared spectroscopy, and scanning electron microscopy (SEM). The re‐crosslinked gel achieves a plugging efficiency of up to 91% and reaches significantly higher plugging pressure compared to the original microspheres. The gel also effectively redirects fluid flow paths, thus expanding the swept range, which is proved by dye tracer experiments. The mechanism of re‐crosslinking and the principle of plugging are further revealed by molecular simulation and Zeta potential analysis. The microspheres have desirable injectability, salt tolerance, and plugging strength. Furthermore, the re‐crosslinking process is controllable, which means flexible operations during field application. As a result, this re‐crosslinkable microsphere system offers an efficient solution for plugging fractures in high‐salinity reservoirs and has broad applicability and significant engineering value.