CCWater – A computer program for chemical classification of geothermal waters

Abstract

CCWater is a computer program developed for the application of extensively being used triangular diagrams for chemical classification and for identification of equilibrium conditions of waters. The program for these diagrams were developed as a Microsoft Excel™ spreadsheet application and compiled using Visual Basic™ 6.0, which has enabled to execute an Excel™ file from a program created by Visual Basic™ 6.0. The performances of all the four diagrams were validated by applying for the same chemical concentration data of the waters that was used by the original authors of these diagrams. The results obtained from this program were consistent with those of the original authors of these diagrams. As an example, CCWater is applied for chemical characterization of thermal waters from springs and geothermal wells of five geothermal fields of Mexico, in which four are electricity producing fields (Cerro Prieto, CPGF; Las Tres Virgenes, LTVGF; Los Azufres, LAGF, and Los Humeros, LHGF) and the fifth geothermal field (La Primavera, LPGF) is in exploration stage. Majority of the reservoir temperatures estimated by Na/K geothermometers from geothermal well waters of CPGF, LAGF, LTVGF, and LPGF are within the limits of accepted differences (within ±20%) comparing to the average BHTs of the respective geothermal well. The good performances of the geothermometers in predicting the reservoir temperatures from well waters is expected because the well waters are fully equilibrated and are of Cl type, thus fulfilling the basic requirements. In contrary, though the spring waters of LHGF and LAGF are of HCO3 type (immature) and exhibited no equilibrium conditions, they also predicted reliable reservoir temperatures. This unusual but important observation in the behavior of the spring waters of LHGF and LAGF was made possible to known by chemical classification of these waters in to different groups and estimation of the reservoir temperatures by considering each water type of a geothermal field as a separate group. This application has shown the importance of chemical type of water and the existing chemical equilibrium conditions in successful using these waters in estimation of the reservoir temperatures, and hence the necessity of the computer program like CCWater. The software CCWater is easy to use, reliable, freely available and will be useful in the application of ternary diagrams for chemical characterization and to evaluate the equilibrium conditions of geothermal waters, particularly during the initial stage of geothermal exploration.