Prevention and treatment of lost circulation with crosslinked polymer material

A process to substantially reduce fluid loss in which an appropriate amount of a non-flowing gel of sufficient strength is emplaced to substantially eliminate or reduce loss of the drilling fluid. The gel composition of the process includes: (1) a non-cellulose containing copolymer having vinyl phosphonate co-monomer units which may be incorporated into the polymer by copolymerization with the other co-monomer(s) comprising the polymer or by grafting upon an already existing polymer or co-polymer, (2) a crosslinking agent active upon the phosphonate groups, (3) a crosslinking initiator comprising a Bronsted Lowry base or Lewis base and (4) an aqueous solvent.