Injection of Waste Geothermal Fluids: Chemical Aspects

Abstract

Deposition of solids from geothermal waters, which occurs when they boil and change temperature, often leads to the formation of troublesome scales. The scale forming solids include ìsimple saltsî, such as calcite, various sulphides and amorphous compounds (silica, Mg-silicate, Alsilicate). Data from Krafla, Iceland, Amatitlan, Guatemala and Momotombo, Nicaragua, have been used to demonstrate the value of chemical thermodynamic methodology to quantitatively assess scaling tendencies from geothermal waters. Such an assessment should be routinely carried out as a part of any geothermal development program to identify optimum conditions for injection of waste geothermal fluids and, at the same time, minimize the need for using inhibitors. The rate of scale formation depends on temperature, the aqueous concentrations of the scale forming components, the degree of supersaturation and kinetics. Desposition of amorphous silica from supersaturated water, which is probably the most troublesome scale, could possibly be reduced, even inhibited, by rapid cooling of the water to <50?C. Mixing of condensate and brine should always be considered as a possible means of preventing scaling in injection wells.