Systematic Study of Geothermal Brine Reinjection for SaltPower Generation Purposes: Citric Acid as a Potential Iron Control Agent

Geothermal brines are concentrated, saline fluids that could be mixed with fresh water to produce “green energy”. By exploiting the large salinity gradient between those fluids, more energy could be harnessed from heat depleted geothermal brines. This study is an attempt to determine the feasibility of adding citric acid to a geothermal brine before dilution. The possible rock-fluid and fluid-fluid interactions that could take place upon reinjection are analyzed though isothermal titration calorimetry (ITC) and core flooding experiments. The results from the ITC experiments show that citric acid in the diluted geothermal brine dissolves iron bearing-carbonate cement. The direct implication of those dynamic interactions is an increment in the rock properties (porosity and permeability), which was also confirmed by coreflooding experiments. Formation damage is only observed when Sønderborg brine and diluted Sønderborg brine were injected into a Berea sandstone core plugs. Those results confirm that the precipitation of Fe(III) oxides inside the porous media could be avoided by the help of citric acid.