to substantially 100 water the produced water may be recirculated to minimize water disposal problems but in that event it will usually be necessary to cool the water prior to reinjecting it since the water temperature exiting from the production well will naturally be considerably higher than the temperature of the water being injected due to its 39 contact with the hot formation if a convenient disposal area is available for the water and an abundant supply of suitable injection water is available the desired temperature reduction may be achieved by simply continuing injecting surface ambient temperature water into the formation in any event it will be necessary to determine the time duration of water injection and this will be accomplished in essentially the same manner as if the water is cooled prior to being injected the method for calculating the injection time necessary to achieve a desired temperature reduction will be given hereinafter below in some situations the practice of the process of our invention involves a cooling process whereby the temperature of the water is reduced either below surface ambient temperature or below the temperature of the water being produced from the production well in the case where produced water is recycled water may be cooled by the use of mechanical refrigeration.