Simultaneous Liquid- and Vapor-Phase Tracer Study in the Tejamaniles Area of the Los Azufres, Mexico, Geothermal Field

Abstract

Comisión Federal de Electricidad (CFE), the owner and operator of the Los Azufres Geothermal field, injects relatively cool (~40°C) produced brines in well Az-08, located in the Tejamaniles (Southwest) area of the field. The present study aims to investigate whether the injected fluid recharges nine production wells in this area, and if it does, to assess the fraction of the injected brine that that recharges each well. Five of the selected wells produce steam and water; the rest produce only steam. For this reason we designed the present simultaneous liquid- and steam-phase tracer study. All nine monitored production wells detected the steam-phase tracer, and the five wells that produce water and steam detected the liquid-phase tracer. For both tracers, all residence curves present a series of peaks, which we interpret as reflecting the fractured nature of the reservoir. These results demonstrated that the feeding areas of the nine monitored wells are recharged from the injector Az-08. The total percentages of tracers recovered in the nine wells at 302 days after the injection were 2.21% for the liquid-phase tracer and 0.0216% for the steam-phase tracer, which implies modest recharge from Az-08. However, these quantities are not final because at 302 days after injection the liquid-phase tracer was still arriving in five wells. Our results reveal upflow (and implied vertical permeability) of steam and water derived from fluid injected in Az-08 over vertical distances 700-1,000 m. This upflow implies (i) that cool injectate is heated enough at depth to convect upwards, thus preventing or at least retarding thermal interference; and (ii) injectate boils at depth generating steam upflow. This provides useful insights on reservoir properties (e.g., temperature, vertical permeability, two-phase conditions) at depth and on the circulation of the injected fluids.