Variation of gaseous species concentration in the Los Azufres geothermal wells as a tool to study the reinjection effect

Abstract

Since 1982 the concentration of gaseous species (CO₂, H₂S, CH₄, N₂, H₂, Ar, and He) has been monitored periodically in theLos Azufres geothermal field, Mich., Mexico by CFE. Here we analyze the variation of gaseous species concentration in order tounderstand the effect of reinjection on the production fluid. The relative proportions of H₂S/CO₂ and N₂/CO₂ are useful parametersto determine the changes in the reservoir characteristics and the effect of reinjection, respectively. Higher values of N₂/CO₂ werefound for all the wells, which are affected by reinjection fluid in the southern zone Tejamaniles, whereas there is no significanteffect of reinjection in the northern zone Maritaro.A N₂-He-Ar triangular diagram is used to estimate the contribution of meteoric (atmospheric), crustal and magmaticcomponents. The wells in Tejamaniles have relatively higher atmospheric component than the wells in Maritaro. In summary thegas geochemistry of geothermal fluids is a powerful tool to study the effect of reinjection.