Copper in Geothermal Brine: Origin, Reactions, Risk and Chances

Abstract

During fluid production at the geothermal research site Groß Schönebeck (Germany) a gradual decline of the production rate and a simultaneous clogging of the bore hole for about 250 m was observed. The fill of the borehole is composed of a mix of mineral precipitates which consist predominantly of native copper (Cu). In this study, we aimed to characterize the source of the Cu, the relevant reactions responsible for its precipitation and to find out if copper represents a severe problem for plant operation. Results showed that high amounts of copper can be expected in certain geological formations (such as the Permian Rotliegend sandstone) where highly saline brine circulates through sandstones and underlying volcanic rocks thereby mobilizing heavy metals. Native copper was found to precipitate due to a redox reaction between the iron (Fe) of the carbon steel liner and dissolved Cu. This reaction was determined, as simulated in lab experiments, to occur quickly at contact between the two elements. Presumably dissolved copper chloride complexes enter the borehole and precipitate immediately at the liner wall. Another lab experiment evidenced that copper also precipitated in the pores of the reservoir rock at the wellbore near area which would have severe impact on the overall well productivity. In turn, copper precipitation once prevented to happen in the production well by appropriate means and kept as dissolved copper in solution, could be exploited at the surface thus being potentially of economic value.