A method of using whole animal blood, or a selected fraction of it, is disclosed as a suitable fluid for assisting recovery of petroleum from a reservoir. Bovine or other animal blood recovered from meat slaughtering is pumped into an oil reservoir from an injection well. It is injected either as a solution with flooding water or followed by water after injection in undiluted form. If desired a clotting retardant, such as citric acid or EDTA (ethylenediaminetetraacetic acid) may be added to the blood to prevent coagulation before contacting fluids in the reservoir. Improved oil recovery from the reservoir over straight water flood is believed to be due to the oil-to-water mobility ratio increase by the addition of blood to the drive fluid. Both blood's high natural viscosity and the ability to polymerize its fibrinogen to form fibrin upon contact with the reservoir rock and fluids are contributing factors. At the same time, its colloidal content, cells and platelets, either as a fraction of, or in the whole blood, tend to plug larger permeability channels of the reservoir rock and thereby inhibit bypassing of petroleum by flood water used to drive reservoir fluids to one or more producing wells.
