Behavior of the Geothermal Reservoir at the Miravalles Geothermal Field During 1994-2010

Abstract

The Miravalles Geothermal Field has been producing electric energy since March 1994. It has provided steam for Unit I (55 MW, installed in 1994), a wellhead unit (5 MW, 1995), Unit 2 (55 MW, 1998) and Unit 3 (29 MW, 2000). A 19 MW “bottoming cycle” plant (Unit 5), completed in January 2004, has brought the total installed capacity in Miravalles to 163 MW. The field has supplied the steam and brine to generate power during more than sixteen years of exploitation (1994-2010). The behavior of production and injection at the Miravalles geothermal field is described, as well as the zone of pressure decline in the reservoir. The micro-seismicity in the field has been increasing since 2001, and even though 2009 has been second in the number of micro-seismic events since 1994, year 2010 seems to be the year of the most micro-seismic events. Until July 2010, there were 165 events registered, with the largest number occurring in May, as was the case in 2009. The events are mainly localized between 1 and 3 km depth and of magnitudes less than 2.9. The micro-seismicity distribution at the Miravalles geothermal field matches the current pressure decline zone.