The Long Term Observed Effect of Air and Water Injection into a Fractured Hydrothermal System

Abstract

Injection of atmospheric air mixed with waste reinjection liquid, has been occurring since 1982 at the Los Azufres, Mexico volcanic hydrothermal system. Several chemical and thermodynamical evidences show that air injection into this fractured geothermal field, could be considered as a long term natural tracer test. Nitrogen and Argon separated from the air mixture migrate from reinjection wells to production zones following preferential paths closely related to high permeability conduits. These paths can be detected, looking into the N2 solubility evolution of production wells. The anisotropic natbre of the fractured volcanic rock, would demand considerably amounts of artificial tracer in order to be detected at the producing wells, specially when fluid extraction is low. This explains the unsuccessful recovery of the artificial tracer tests performed in past years at Tejamaniles, the southern field's sector. On the other hand, chloride concentrations and other salts, are increasing in the liquid produced by the oldest wells of the sector.