Geochemical Assessment of the San Jacinto Tizate Geothermal Field, Nicaragua
Gunter E. GAMEZ
[Polaris Energy Nicaragua, S.A., Nicaragua]
The Geothermal Field San Jacinto Tizate is in the western part of Nicaragua, 75 km north from the capital, with an area of 6 km2. It currently has an installed capacity of 77 MW. The reservoir of the Geothermal Field is liquid dominant with temperatures in the range of 227-291°C, determined through deep logs. As the geothermal resource is exploitered, chemical changes are observed in the reservoir and, therefore, it is important to characterize and interpret the geochemical evolution of the Geothermal Field. An evaluation of the reservoir chemistry is presented, based on geochemical methods, to analyze and interpret the different processes that affect the reservoir. The reservoir engineering area oversees processing and analyzing the chemical data obtained from monitoring the field, and for this evaluation an average of the data obtained was made every six months. An individual interpretation was made for each well and it was possible to identify wells that present processes such as: cooling by boiling in the nearby areas and, in some cases, furthest away from the feeding zones of the wells, with this it is inferred that there are different thermal and hydraulic characteristics in the different zones of the geothermal reservoir. In addition, there are wells that are in equilibrium with respect to the analysis of Emed, ENaKCa and ESiO2, which indicates that there are no extreme temperature changes around the reservoir and well feed. The Giggenbach diagram shows the evaporation succession process at the beginning of production of some wells, as an explanation for the excess steam found in certain areas of the field (except for wells SJ6-1 and SJ9-1, which at the beginning present an infiltration of lower temperature waters). In the analysis of gases with the FT & HSH Diagram, changes were observed such as: increase in the steam fraction and decrease in temperature in the wells, decrease in the steam fraction with an increase in temperature, constant behavior of the steam fraction with increase in temperature, among others. These are indicative of processes that occurred in the wells whose reflection in the gases was of great importance for the interpretation. Through the use of isotope, chloride and enthalpy diagrams, mineral equilibrium and N2-He-Ar Giggenbach triangular diagram, an integrated interpretation was made that was related to the individual interpretation of the evaluated wells, resulting in the identification of three important zones of the reservoir: zone of ascent of hot equilibrium fluids in enthalpies and conditions close to boiling point; transition zone reflecting conditions of the directions of movement of fluids from the reservoir to their discharge, and a zone of influence of lower temperature water indicative of a border zone of the exploitable field.
|        Topic: Geochemistry||Paper Number: 14120|