Characteristics of Basin and Range Geothermal Systems with Fluid Temperatures of 150°C to 200°C

Abstract

Six geothermal reservoirs with fluid temperatures over 200°C and ten geothermal systems with measured fluid temperatures of 150-200°C have been discovered in the northern Basin and Range Province of the USA. A comparison of these high and moderate temperature systems shows considerable overlap in geographical distribution, geology, and physical properties. Our ability to distinguish between moderate and high temperature systems using fluid chemistry has been limited by often inaccurate estimates based on shallow samples and by a bias in the NaKCa geothermometer which, in this province, overestimates fluid temperatures at economic drilling depths for both shallow and deep samples. The best indications of a possible high temperatures reservoir near a moderate temperature well appear to be silica base temperatures above 210°C for deep fluid entries and a high temperate gradient in the bottom of the well.