Initial temperature distribution in the Mamotombo geothermal field, Nicaragua

Abstract

An analysis and interpretation is given of the initial temperature distribution in the Momotombo high temperature field, Nicaragua, Central America. The study was based fundamentally on more than 500 downhole temperature measurements and a mineralogical study of 1/3 of the wells. A database was used to estimate initial and alteration temperatures in each well. Then temperature cross and plane sections of the field were made which were analyzed for the construction of a conceptual model for the reservoir. The geothermal field is divided into two reservoirs. A hot deep upflow zone with a temperature range of 250-290 C, which is located in the western part of the field at >1000 m u.s.l. The deep reservoir feeds a shallow and horizontal reservoir at 200-400 m u.s.l., which has a temperature range of 200-230 C. Both reservoirs are liquid dominated. An equilibrium between alteration and initial temperature seems to exist in most of the wells analyzed. However, in the southeastern part of the field are signals of natural cooling, observed as inflow of <100 C water into the geothermal system. The areal extent of the deep reservoir is unknown to north and west. Future drilling should be directed to this part of the field as the geothermal reservoir has not yet been bounded by drilling in these directions.