US Patent 9464504 Enhancing delaying in situ gelation of water shutoff systems

Gel compositions include a high molecular weight water-soluble acrylamide polymer, a crosslinking system capable of crosslinking the polymer, a crosslink delay system and an aqueous solvent. The gel compositions are prepared at the surface and injected into a zone of a formation assessable by a wellbore to form a continuous single-phase gel. The gel compositions may be tailored to a specific formation by predetermining gelation rate, gel strength and/or gel stability to form gels having predetermined properties suitable for the zone.