A Study of Reinjection and Connectivity Between Wells in the Los Azufres (Mexico) Geothermal Field

Abstract

Historical records of production and reservoir-monitoring data gathered in the Los Azufres geothermal field were studied to assess the effect of geothermal reinjection and the connectivity among geothermal wells. The former data correspond to wells producing vapor or a liquid-vapor mixture. To estimate the connectivity between pairs of injection-production wells, the known nonparametric regression ACE (Alternating Conditional Expectation) method was used to correlate injection rate histories to either chloride concentration histories for liquid/mixture production wells or to bottom-hole pressure histories for vapor production wells. The statistical results were analyzed in light of earlier field studies based on tracer tests as well as on histories of both chemical species and isotope concentrations. Our study assessed the relative effect of reinjection through monitoring chloride concentration and, for the first time, bottom-hole pressure histories measured at production wells of both southern and northern Los Azufres geothermal field. Our analysis suggests that the connectivity indices yielded by the ACE method for some well pairs are in agreement with earlier reservoir data. Further comparison with other types of reservoir data is required to evaluate or calibrate our estimations.