Comparative Studies of Geothermal Surveys in 3-Meter and Temperature-Gradient Holes

Abstract

The reliability of conducing temperature surveys within the upper 3 meters of the surface to map geothermal anomalies is demonstrated in experiments at two prospects in which deep gradient hole data were obtained. The 3 m temperatures faithfully outlined the thermal anomaly at McCoy, Nevada; and in Dixie Valley, NV 3 m surveys reproduced and detailed patterns derived from 40 m data. These encouraging results led to the development of multi thermistor strings for logging the seasonal wave within the upper 3 meters. From many such logs, diffusivity variations can be detected, which might otherwise be misconstrued as thermal anomalies. The technique is demonstrated by a typical Basin-Range reconnaissance project. As many as 10 or more 3 m holes can be emplaced in the time required for a conventional gradient well, and with considerably less impact on the environment.