Research Progress of Polyacrylamide Gels for Oilfield Applications: A Systematic Review

In the middle-to-late stage of reservoir development, widespread high-permeability channeling exacerbates ineffective water circulation and impairs crude oil recovery. This work explores polyacrylamide (PAM) gels intended for oilfield profile control and water shut-off. It comprehensively compares gelation behaviors and performance metrics of diverse cross-linking and modification strategies, and pinpoints critical unresolved research gaps. Four representative PAM-gel systems are analyzed in detail, including organic-crosslinked, metal-crosslinked, nano-composite-modified, and delayed-crosslinker formulations. The results show that polyethyleneimine (PEI) cross-linked gels achieve a storage modulus of 780 kPa at 110 °C, which is superior to the conventional hydroquinone-hexamethylenetetramine (HQ-HMTA) system. Metal-crosslinked gels are prone to syneresis and structural instability above 70 °C. Nanocomposite modification significantly enhances gel comprehensive properties: nano-silica improves thermal resistance to 155.5 °C; modified nano-graphite doubles storage modulus (G'), shortens gelation time by half, and maintains 76.5% of initial modulus after 60-day aging at 130 °C; TOCN-reinforced gels preserve structural integrity under high-salinity environments at 140 °C for 108 h. Delayed-release cross-linkers can extend gelation time up to 17 days to meet the demands of deep in situ profile control. Furthermore, the emerging data-driven paradigm of artificial-intelligence-assisted gel optimization is also reviewed, together with its current limitations. Future research priorities cover intelligent responsive gel materials, environmentally benign cross-linkers, and unified evaluation specifications for heterogeneous reservoirs. This paper reviews over 100 core publications from 2000 to 2026 based on the Web of Science and Engineering Village databases. Different from existing studies, this work emphasizes the molecular crosslinker mechanisms, nanomodification reinforcement, and field performance variations of PAM gel systems, and concludes the major technical bottlenecks for their application in harsh reservoirs. Meanwhile, it quantitatively compares the performance of modified PAM gel formulations and clarifies the applicable temperature ranges of different crosslinker schemes, providing technical references for the development of PAM plugging agents for complex oil reservoirs.