Crosslinkable-polymer compositions that comprise a chitosan-based compound and a phenol source, and associated methods, are provided. Various methods of use are also provided. In one embodiment, the methods comprise providing a crosslinkable-polymer composition comprising an aqueous fluid, a chitosan-based compound, a chitosan-reacting polymer, and a phenol source; introducing the crosslinkable-polymer composition into the portion of the subterranean formation; and allowing the crosslinkable-polymer composition to form a crosslinked gel in the portion of the subterranean formation.