Method for preparing dilute polymer solutions

Claim 1

A process for preparing a uniform dilute aqueous polymer solution used in enhanced oil recovery from a subterranean oil-bearing formation comprising: forming a slug of a polymerization mixture comprising a polymerizable substance and a polymerization initiator; introducing the slug into a polymerization vessel having an inlet and an outlet; repeating the formation of additional slugs of the polymerization mixture and sequentially introducing each additional slug into the polymerization vessel to form a reaction gradient between the slugs such that substantially no mixing occurs between each slug; controlling the rate of continuous movement of each slug in the polymerization vessel from the inlet to the outlet so that each slug is essentially completely polymerized to a polymer slug at the outlet; successively and continuously removing each polymer slug from the outlet; forming a reaction mixture by continuously introducing into each polymer slug a modifying agent capable of reacting with the polymer; continuously introducing the reaction mixture into a reaction vessel having an inlet and an outlet; controlling the rate of continuous movement of the reaction mixture in the reaction vessel from the inlet to the outlet such that the reaction between the polymer and the modifying agent is essentially complete at the outlet, forming a concentrated product solution; continuously removing the concentrated product solution from the outlet of the reaction vessel; mixing the concentrated product solution with an aqueous diluent without substantially degrading the polymer to obtain a nonuniform mixture of the concentrated product solution and aqueous diluent; introducing the nonuniform mixture into a dilution vessel; and maintaining the nonuniform mixture in the dilution vessel for a time sufficient to convert the nonuniform mixture to a uniform dilute polymer solution having a lower polymer concentration than the concentrated product solution.