ASSESSING RARE EARTH ELEMENT PATTERNS IN PRODUCED WATERS USING GEOCHEMICAL SPECIATION MODELING

The ubiquitous nature of rare earth elements (REE) in the geosphere has prompted a search for unconventional sources, such as byproducts from oil, gas, and geothermal industries. In 2018, 224 produced water samples from oil wells and geothermal waters in western U. S. basins were analyzed for REE concentrations in addition to major element chemistry (DOE Award Number: DE-EE0007603). Analyses showed that NASC-normalized REE patterns were consistent within each basin but varied across basins. Factors controlling REE variability between basins were not identified in the initial report, and REE patterns were not linked to lithology, reservoir temperature, or salinity. Understanding the cause of spatially controlled variations in REE patterns requires constraining how REE mobilize and concentrate in each basin system. We apply geochemical speciation modeling to elucidate potential causes for these basin-specific signatures. Using the geochemical modeling software Geochemist’s Workbench (GWB), we compare the complexation behaviors of REE in produced and thermal waters. The availability of ligands and presence of competing ions in each sample determines the ability for REE to complex, therefore influencing mobility and concentration. Our results shed light on how variations in water chemistries between basins impact REE patterns and give insight into which basins should be targeted for future REE extraction.