Production characteristics of the Monotombo geothermal field, Nicaragua

Abstract

An analysis and interpretation is given of eight years of fluid production from the Momotombo high temperature field, Nicaragua. The study consisted of a careful analysis of the measurement methods used to estimate total flowrates and enthalpies from geothermal wells. Then, all available production data from Momotombo were collected and plotted with time. The cumulative production from the field was also calculated. Based on these calculations, a volumetric analysis was performed. The eight years of production have induced a pressure drawdown of more than 20 bars in the shallower part of the Momotombo reservoir. The drawdown has initiated extensive boiling in the reservoir. Now three zones of reservoir conditions can be found in the initially liquid-saturated reservoir; a dry steam zone between approximately 150 - 250 m b.s.l., a two-phase zone between 250 and 320 m b.s.l., and a saturated liquid zone at depths greater than 320 m b.s.l.. The cumulative mass production from the field is on the order of 60 million tons. Volumetric analysis of fluid in storage indicates that 40% of the produced mass has been taken from the shallow reservoir, 35% is fed by natural recharge to the system and 25% by reinjection and production from deep reservoir wells. If these proportions remain the same in the future, only 6 to 10 years may pass until the shallow reservoir is fully depleted.