Oil recovery by waterflooding employing cross-linked polysaccharides for mobility control

Claim 1

In a method for the recovery of oil from a subterranean oil reservoir penetrated by spaced injection and production systems wherein an aqueous fluid is introduced into said reservoir via said injection system to displace oil to said production system, the improvement comprising: employing as at least a portion of the fluid introduced into said reservoir an aqueous solution of a viscosifier comprising the water soluble reaction product of an organic polyisocyanate having at least two reactive isocyanato groups and the addition product of an alkylene oxide and a linear, non-ionic polysaccharide, said addition product having a molecular weight of at least about 100,000, said alkylene oxide having the formula ##STR3## wherein R 1 , R 2 , R 3 and R 4 are the same or different and are selected from the class consisting of hydrogen and lower alkyl groups containing from one to five carbon atoms, said linear, non-ionic polysaccharide formed of repeating structural units having the formula ##STR4## said addition product being cross linked by said polyisocyanate such that there is a minimum of an average of one cross link for every 2,000 of said repeating structural units up to a maximum of an average of one cross link for every 20 of said repeating structural units.