Practical Uses of Clay Minerals at the Miravalles Geothermal Field, Costa Rica

Abstract

In geothermal resources development the different hydrothermal alteration products are of interest as a source of information. Due to their formation conditions, the clay minerals have great relevance as geothermometers, allowing information top be obtained related to the existing formation temperature of the rocks during the drilling processes. This paper presents clay minerals data for the Miravalles Geothermal Field, where there is a relationship between the different clay minerals and the temperature variations with depth. The method developed included the elaboration of tables for an easy correlation between the diffractograms results and the estimation of the rock formation temperature. The geothermometer developed has proved to be reliable for the case of the Miravalles Geothermal Field, in the temperature range of 150-220 ?C. The application of this method during the drilling process allows continuous information to be obtained on the existing clay minerals, the thermal evolution of the rock formation and the determination of commercial temperatures for geothermal exploitation. The method also reduces considerably the direct temperature measurements during the drilling, and at the same time reduces the breakdown risks, drilling time and the final costs of the well. Finally, the rock formation temperatures inferred can be used for modeling purposes, giving an idea of the thermal behavior of the field some time before the thermal recovery and stabilization of every well.