No abstract

Gas data of the Los Azufres geothermal field were analyzed using a method based on equilibrium of the Fischer-Tropsch (FT) reaction: CH4 + 2H2O = 4H2 +CO2 and on the combined pyrite-hematite-magnetite (HSH2) reactions: 5/4 H2 +3/2 FeS2 +3/4 Fe2O3 + 7/4 H2O = 3 H2S +Fe3O4 in order to estimate reservoir temperature and excess steam. The solution of equilibrium equations produces a grid (FT-HSH2). This method is suitable for reservoirs with relatively high H2S but low H2 and NH3 concentrations in the fluid as is the case of the Los Azufres well discharges. Reservoir temperature and reservoir excess steam values were estimated for initial and present conditions in representative wells of the field to study the evolution of fluids, because of exploitation and waste fluids reinjection. This method was very useful in estimating reservoir temperatures in vapor wells, while in two-phase wells it was found that as the well produces a smaller fraction of water, the reservoir temperature estimation agrees qualitatively with results from cationic or silica geothermometers. For liquid-dominated wells the reservoir temperature estimations agree with temperatures obtained from the well simulator WELFLO. This indicates that FT-HSH2 results provide the temperature of the fluid entering the well where the last equilibrium occurs. Results show a decrease in reservoir temperatures in the southern zone of the field where intensive reinjection takes place. With exploitation, it was also noted that the deep liquid phase in the reservoir is changing to two-phase increasing the reservoir steam fraction and the non-condensable gases in well discharges.

La curva­tipo geotérmica afectada por daño sirve para determinar el efecto de daño en un pozo y para caracterizarlo. Esta metodología puede ser aplicada para determinar el efecto del daño en los pozos que no pueden ser retirados de la explotación continua. Comúnmente se emplean los análisis de las pruebas transitorias de presión, cuya ejecución es tardada. En los pozos analizados, el efecto de daño aumenta con su tiempo de explotación y está relacionado con el deterioro en la producción. El conocimiento del daño ayuda a la toma de decisiones acerca de las operaciones a aplicar en el pozo con el objeto de mejorar su productividad.

The thermal evolution of Los Humeros geothermal fluids was estimated by using liquid and gas chemical geothermometers and results indicate two separated fluid entries to the wells: a (~250°C) liquid produced from a shallower reservoir and a (>300°C) steam produced by a deeper stratum. Both entries were identified by Na/K and SiO 2 geothermometers for the liquid and H 2 /Ar for the steam. CO 2 /Ar geothermometer seems to provide temperatures of mixed fluids entering the wells. Based on thermal evolution of fluids, multiple fluid entries in wells were characterized while reservoir exploitation-related processes like cooler water entries and condensation phenomena, were also identified.