Editorial for the Special Issue "Advances and Applications of Polymer Gels for Subsurface Energy and Storage".

Polymer gels are essential functional materials for subsurface energy operations, playing a critical role in conformance control, fluid diversion, hydraulic fracturing, and leakage mitigation. As reservoirs become increasingly complex and the demand for sustainable energy grows, continued innovation in gel technologies is crucial. This editorial introduces a Special Issue titled "Advances and Applications of Polymer Gels for Subsurface Energy and Storage," which compiles seven original research articles exploring recent developments in gel synthesis, characterization, and applications. The featured studies highlight the versatility of polymer gels, including nanoparticle-reinforced composites, foam-gel hybrids, recrosslinkable preformed particle gels, and advanced fracturing fluids. The contributions address key challenges across CO2-enhanced oil recovery, heavy oil production, low-permeability reservoir fracturing, and combined enhanced oil recovery strategies. The findings demonstrate ongoing efforts to tailor gel systems for harsh reservoir conditions, improve sweep efficiency, and reduce formation damage, fostering more efficient and sustainable subsurface engineering practices. This Special Issue serves as a valuable resource for researchers and practitioners advancing polymer gel technologies for energy and storage applications.