Over the last 15 years two geothermal fields have been under commercial 
exploitation in El Salvador, the Ahuachapán and Berlin fields. They are located 
to the western and the eastern part of the country, respectively. In order to 
achieve the requirement of energy production and to contribute in the 
sustainable development, the reservoir engineering is undertaken several 
activities. The monitoring is the main source of information and the first view 
that is happening into the geothermal system and reservoir. Mass flow rate, 
enthalpy, wellhead pressure, fluid chemistry are only a few parts of the 
continuous monitoring that has to be done. Pressure declining is the most 
common effect when the reservoir yield mass. The Ahuachapán field declined 
15 bar at the beginning, but during the last 10 years the decline was 2-3 bar, 
however Berlin was declined around of 14 bar for the 
last 15 years. 
Boiling and dilution seems to be the largest process happening in the reservoir. Thermal 
breakthrough due to injection is not evident yet in both fields, in spite of some 
pressure recharge, which has also been also observed at the neighboring 
wells. Numerical modeling is another important issue for the reservoir 
management. Several models are normally used and they are continuously up 
dated for more confident forecasting. The reservoir engineering is contributing 
to produce at least 1,150 GWhe per year, equivalent to 
20% of the total electricity consumption in El Salvador.

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