Chemical evolution of the Momotombo reservoir and silica and calcite scaling potential of the fluid

Abstract

The Momotombo geothermal field has been in operation for almost 30 years and currently eight production wells sustain a gross capacity of 27 MWe. This report describes the chemical trends of the Momotombo reservoir fluid during the last years. The WATCH program was used to calculate the composition of the deep liquid. Quartz and Na/K geothermometers were used to compute an average temperature for each well. One of the most evident changes in the chemical composition of the fluid is shown by the chloride content. In 1990 the chloride content was high, but now a strong decrease is notable; this is due to both the incursion of cold water due to exploitation. The quartz and Na-K geothermometers show indications of the presence of cold recharge water in most wells. However, an increase in temperature was observed in well MT-36, which suggests the influence of hot water from depth. The scaling tendency of the Momotombo fluid during boiling was evaluated using the WATCH program. The calcite scaling potential has increased from 1990 to 2012.