Tracer Testing at Los Humeros, Mexico, High-Enthalpy Geothermal Field

Abstract

We performed a tracer study in the high-enthalpy Los Humeros, Mexico, geothermal reservoir to assess the effects of produced-brine injection in a major part of the field. The reservoir is emplaced in fractured volcanic formations. A high-temperature, liquid-phase tracer, 2,6 naphthalene disulfonate, was used. Our results revealed that injection in well H-13 recharges the feeding zones of the nine monitored producing wells. Our results also indicate there is negligible risk of thermal interference in the observed wells at the injection rates of this study. The observed small aggregated tracer recovery suggests that most of the injected fluid, perhaps up to about 99%, flows to the deep reservoir, recharging it and enhancing its economic life. In this field the tracer residence curves present unusual patterns, as revealed in previous and the present study. We investigated the causes of these unusual patterns by measuring, for each well, the electric conductivity of the samples. Then we found a linear correlation between the mean electric conductivity of the samples with the average liquid fraction in the corresponding discharge. On this basis we concluded the main cause of the observed unusual patterns is that each production well monitored probably has at least two feeding zones with differing enthalpies.