Effectiveness of 2-Meter and Geoprobe Shallow Temperature Surveys in Early Stage Geothermal Exploration

Abstract

Cost-effective geothermal exploration involves a stepwise approach wherein the least expensive tools that can advance (or reject) a property should be considered prior to more expensive techniques. Coolbaugh et al. (2007) demonstrated that shallow (2-meter) surveys were a cost-effective “direct push” tool that can identify and delineate geothermal outflow zones, prior to more expensive temperature gradient drilling. This paper evaluates the Geoprobe as another early-stage, direct push exploration tool that can collect water samples and temperature data at depths intermediate between 2 meters and typical temperature gradient drilling. In addition, the temperature relationship between surface anomalies identified by 2-meter surveys and the deeper thermal regime is explored. To do this, 2-meter and Geoprobe surveys were conducted at three representative locations in Nevada: McGee Mountain in northern Humboldt County, the Hot Pot, in eastern Humboldt County, and Teels Marsh, in Mineral County. Geoprobe temperature measurements at 8-30 meter depths largely confirmed those from the shallow 2-meter measurements. At Teels Marsh, two surface thermal anomalies were found to have temperatures of 78oC and 97oC at shallow depth. In addition, water samples from the Geoprobe at these anomalies displayed encouraging geothermometry, enhancing the property’s appeal. Thus, Geoprobe sampling should be considered as a potential next-step tool after 2-meter surveys, in appropriate geological environments.