New Data from an Old Well: Changes in the Chemistry of Runoff Geothermal Well Water

Abstract

Water samples from human-made geothermal wells are challenging to collect. The water at the wellhead is often above its boiling point and pressurized. Because these traits make water sampling difficult, even low-temperature geothermal wells often are sampled after the water has cooled, decompressed, and interacted with some atmospheric air. Work with natural geothermal features has shown that waters rapidly re-equilibrate after reaching the surface (Lewicki, 2013). When geothermal well waters must be sampled far from a wellhead, has the damage already been done? The Center for Economic Geology Research at the University of Wyoming recently sampled from a recharge-pressurized low-temperature geothermal well in Wyoming's Great Divide Basin. The well has likely been flowing ever since it was abandoned shortly after completion in 1925. The age and disrepair of this well have resulted in a significant amount of bore scale and temperature equilibration in the ground near the well bore. A series of samples were taken starting inside the bore then at several points along the run-off stream until it terminates in an evaporate lake. These samples showed that some species equilibrate rapidly and as predicted, but that many other species remained consistent until the run-off stream terminated in an evaporate lake, at which point significant changes in almost every analyte occurred. This study shows that most analytes of interest to geothermal operations can be sampled further from the wellhead than previously thought, but only if evaporation is minimized.