Reservoir Assessment of Zuni I and II Geothermal Fields, Guatemala

Abstract

A conceptual model for Zunil I and II is presented from careful analysis of reservoir temperatures and initial pressures. The Zunil I reservoir is divided into an upper and lower reservoir by a lithological contact between a granitic formation and overlying volcanic rocks. Wells producing from the upper reservoir yield less total output while wells that produce from deeper reservoir have higher total outputs. There appears to be a main upflow in the western part of Zunil I at the intersection of northeast and northwest regional fault trends. A second upflow may be present near the eastern edge of Zunil I, possibly connected as a line source along a northeast trending fault to the main upflow in the western area. Pressure potentials are highest in the west, suggesting fluid upflow, with outflows to the northeast and east. The Zunil II area shows that temperatures are overall higher at shallower depths with a source upflow possibly located in the southeast area. Temperature and pressure distributions suggest that fluids are flow to the northwest. A volumetric assessment of the Zunil II reserve shows that there is a potential for 35 MWe for the next 35 years.