An Update of the Los Azufres Geothermal Field, after 21 Years of Exploitation

Abstract

Los Azufres geothermal field, in the central portion of MÈxico, is located in the volcanic belt, at an average elevation of 2800 masl. It has been under commercial exploitation to generate electricity since 1982. At present, the installed capacity is 188 MW with seven backpressure units of 5 MW each, two binary cycle units of 1.5 MW each, one condensing unit of 50 MW and four new condensing units of 25 MW each. In order to sustain the generation, steam is supplied from 43 producing wells and brine is injected into seven injectors wells. In 21 years of continuous development, 120.3 million of tons of steam have been extracted. The Los Azufres hydrothermal system was studied thoroughly from the beginning of exploitation. Currently numerous geochemical, production and subsurface log data permit, in conjuntion with geological, geophysical and mineralogycal studies, the development of a conceptual model of the field and a reliable analysis of the evolution of the reservoir using numerical simulators. The average pressure decline in the south zone of the field is 0.71 bar/year and in the north zone is 0.33 bar/year. Decline in the south is higher than in the north because of the larger extraction of mass and energy. Those numbers are consistentes with the extration of fluids in the field. The numerical models show the feasibility of generating at least 120 MW in the north zone and 133 MW in the south, for more than 20 years of production. However, because of the four condensing units of 25 MW each, are generating electricity recently, since 2003, and mass extraction of the reservoir was duplicated , it is necessary to observe the behavior of wells and reservoir in order to verify the real pressure and mass declination versus the obtained from numerical models.