A number of technical difficulties are encountered in producing geothermal energy from reservoirs containing brines with high concentrations of dissolved solids. The reduction in temperature and pressure associated with brine production results in the precipitation of solids which can form heavy scale in producing and injection wells and in surface equipment. Evidently under many conditions precipitates form in the reservoir surrounding producing wells, thereby reducing their productivity. some cases the precipitation of solids is so severe that it can prevent economic production.

This paper presents results of an investigation of the possibility of injecting a different water in a geothermal reservoir as a means of reducing problems caused by solids precipitation and scale formation. Corrosion problems may also be reduced depending upon the water-rock-metal behavior. The results are confined chiefly to reservoir mechanics, a logical first step in evaluating the process for a given reservoir. Water-rock chemistry, water treating, water supply, brine disposal and overall economics are discussed only briefly or are beyond the scope of this paper.

In general the composition of water injected into geothermal reservoirs does not remain the same. the injected water tends to equilibrate with the reservoir rock. fresh water is injected it may pick up such minerals as silica, carbonate, iron, sulphur, etc. These minerals may precipitate and cause problems in producing the reservoir. Nevertheless, under suitable conditions, a change in the reservoir water may be an attractive alternative to cycling the original reservoir brine.

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