Update Report and Expansion Strategy for Los Azufres Geothermal Field

Abstract

In June 2003, the ComisiÛn Federal de Electricidad (CFE) of MÈxico commissioned an additional 100 MWe of generation capacity at the Azufres Geothermal Field, which presently generates a total of 188 MWe from seven 5 MWe back-pressure turbines, 150 MWe of condensing turbines and 3 MWe of binary units. After producing for 21 years, many wells in the field have developed two-phase zones, but reservoir pressures and production rates have declined within reasonable limits. In 2003, CFE contracted the services of GeothermEx, Inc. of Richmond, California, to conduct an independent resource evaluation of the Azufres field. This work included an update of the conceptual model, and the development of a numerical model that would reproduce the initial state and the historical behavior of the reservoir, and could be used as a tool for forecasting the reservoir response under different field management scenarios. The data available included measured subsurface temperatures and historical production data collected since exploitation of the field began.
A dual-porosity numerical model was developed using the Tetrad modeling software, and good matches were obtained to the initial-state conditions as well as the available historical production data. The results indicated that the field is capable of supporting a generation load of 188 MWe (with the present power plant configuration) over a 30-year period, by drilling several additional make-up wells. It also predicted that the reservoir could support up to 250 MWe of total generation by drilling additional wells in unexploited areas of the field. This document presents the strategy developed for maintaining the steam supply through work-overs and acid treatments of the existing wells, describes the proposed zones for drilling new wells for future expansion, and discusses the benefit of repowering the back-pressure turbines with bottoming binary units, which could increase the total capacity of the field to 287.5 MWe.