A Status Report on the Exploitation Conditions of the Ahuachapan Geothermal Field

The present exploitation conditions of the Ahuachapan field are discussed. The high well density in a small area has resulted in a significant reservoir pressure decrease due to the inherent reservoir over-exploitation. The average pressure in the exploitation zone has decreased from the 1975 value of 34 kg/cm{sup 2} to the May 1983 value of 23 kg/cm{sup 2}. The production decline characteristics of the Ahuachapan wells were examined, concluding that all wells but Ah-22 show exponential decline. The cumulative production-reinjection for the field up to April 1983 is 159.090 x 10{sup 6} tons, and 37.592 x 10{sup 6} tons, respectively. The effect of reinjection upon field behavior is evident when observing the pressure decline characteristics of the field. It is seen that for indection fraction related to total mass extracted above 30 percent, the average decline pressure in the production area becomes approximately stabilized. If this condition is not met the reservoir pressure decreases sharply. From this finding it is concluded that a careful and properly planned reinjection program is a must for the field. The observed temperature reduction in some of the wells seems to be the result of two operating mechanisms. First, we have the pressure decline that produces water vaporization and the consequent temperature descend. Analysis of information available shows no clear indication of deleterious temperature effects on the producing wells due to injection. The only exception observed to date is well Ah-5 that because its close distance and its relative structural position and direct hydraulic connection to injector Ah-29, presented conditions for fast displacement of the thermal front, resulting in unsufficient contact area and residence time for reheating of the injected water