Abstract: A method and system for the downhole separation and injection of surface water and water contained in a produced mixture from an underground formation of a hydrocarbon well containing hydrocarbon and water. Downhole separation of the produced mixture into a predominately water component and predominately hydrocarbon component is achieved using an oil-water separator. Surface water is delivered to a downhole fluid-driven pump under pressure so as to drive the pump. The downhole-separated predominately water component of the produced mixture is directed to the pump, by way of the pump and combined with surface water to obtain a combined fluid. The combined fluid is directed to a downhole injection formation by way of the pump. Oil is transported to the head of the well either naturally under the eruptive force of the well, or with the assistance of regular artificial lift methods, including gas-lift.

Abstract: A method and system for the downhole separation and injection of a predominately water component of the mixture produced from a naturally flowing or gas-lifted hydrocarbon well. The produced mixture is delivered to a separator located in the wellbore above an injection formation, the separator comprising a gas-liquid separator and an oil-water separator. The produced mixture is admitted to a gas-liquid separator to separate the free gas from the produced mixture. The gas-depleted produced mixture is then admitted to an oil-water separator where the produced mixture is separated into a predominately water component and a predominately hydrocarbon component. The separated gas and the predominately hydrocarbon component are delivered to the surface, separately or commingled. The predominately water is injected in the injection formation accessible through the same wellbore, and located below the separator.