STEEL ROUGHNESS EVOLUTION UPON EXPOSURE TO DILUTE FLUIDS OF VARIED REDOX POTENTIAL: IMPLICATIONS FOR GEOTHERMAL DEVELOPMENT

Of the many alternative energy sources available, geothermal is perhaps the most overlooked and underutilized. Deep direct use enhanced geothermal systems have recently gained interest as an emerging technology in which the traditionally off-limits thick sedimentary basins could become viable energy producers-offering a potentially tremendous source of clean energy. However, at the fluid-steel interface, corrosion is a significant problem. At the surface of a low-temperature geothermal power plant, and once the heat energy has been extracted, the working fluid is often reinjected into the subsurface reservoir at a temperature of ~80 ^oC. In this work, we explored the degradation of Q125 steel (suitable well casing material for deep direct use geothermal systems) upon exposure to pH-normalized, low ionic strength fluids of differing redox ORP. The experiments were performed at one atmosphere of pressure and at 80 ^oC over a total elapsed time of 1200 hours. The corrosive effects on the Q125 steel have been determined via atomic force microscopy where the surface roughness will be measured and compared to results prior to brine exposure. Additionally, a mass-loss corrosion rate has been calculated and provides insight into the quantity of steel which is being removed over time. Results from both ORP-varied, low ionic strength fluids, the steel surface will not only become progressively rougher over time, but that the fluid pH and Eh evolves considerably from its initial composition. Steel corrosion studies provide meaningful information regarding the lifespan and suitability of material preference in industrial settings such as geothermal operations, and will be important for the implementation of this alternative energy source.