Method for preparing polymer solutions

Claim 1

A process for the preparation of aqueous polymer solutions for use in secondary or tertiary recovery of oil from a subterranean oil-bearing formation comprising: forming a first volume of a first reaction mixture comprising a polymerizable substance and a polymerization initiator; introducing the first volume of the first reaction mixture into a first reaction vessel having an inlet and an outlet; repeating at regular predetermined intervals the formation of additional volumes of the first reaction mixture and sequentially introducing each additional volume into the first reaction vessel in a manner such that a substantially stable interface forms between each adjacent volume and substantially no mixing occurs between each volume; controlling the rate of movement of each volume of the first reaction mixture in the first reaction vessel from the inlet to the outlet thereof in a manner such that, as each volume of the first reaction mixture is continuously moved through the reaction vessel, the extent of polymerization of the polymerizable substance in each volume differs from that of every other volume in the first reaction vessel and the polymerization of the polymerizable substance in each volume is essentially complete, forming a polymer solution, when each volume successively reaches the outlet of the first reaction vessel; successively and continuously removing each volume of the polymer solution from the outlet of the first reaction vessel; forming a second reaction mixture by continuously introducing a dilution water in an amount less than that which causes free water to substantially separate from the polymer solution and a modifying agent capable of reacting with the polymer in the solution into each volume of polymer solution; continuously introducing the second reaction mixture into a second reaction vessel having an inlet and an outlet; controlling the rate of movement of the second reaction mixture in the second reaction vessel from the inlet to the outlet thereof in a manner such that the reaction between the polymer and the modifying agent is essentially complete, forming a product solution, when the second reaction mixture reaches the outlet of the second reaction vessel; continuously removing the product solution from the outlet of the second reaction vessel; and diluting the product solution prior to injecting it via a well into the subterranean oil-bearing formation.