Assessing Geothermal Areas During Drilling

Abstract

The drilling of a geothermal prospect is not always rewarded with the discovery of a geothermal reservoir. Some prospects have alternating hot and cold aquifers. Anomalously high heat flow can be caused by shallow circulation of moderate temperature fluids. Thus, the drill may penetrate relatively cool rocks at depth rather than high temperature aquifers. We suggest that date collected and analyzed in near real time can be used to predict reservoir conditions at greater depth. On the basis of preliminary examination of the core from Coso, California, we speculate that low thermal gradients will probably occur at depth. The presence of extensive fracturing and low temperature alteration products in many fractures indicated widespread circulation. A more thorough study of the fracture, mineral content, temperatures, and rock properties obtained during drilling would sharpen our capabilities.