Analysis of wellbore temperatures in the Mamotombo geothermal field, Nicaragua

Abstract

This report is a study of changes in temperature, pressure and enthalpy in the Momotombo high temperature geothermal field, Nicaragua, Central America. The downhole data considered in this report was collected in 33 of the 39 wells in the field. A simple database was created on a PC personal computer for storing and processing the data, which consisted of 522 downhole temperature measurements and 45 pressure measurements. The measurements were carried out between 1975 and 1989. All these measurements are presented in supplementary appendix B of this report. A study of the reservoir temperature history shows that the northeast part of the well field has cooled down at a rate of up to 6 C/year. Other parts of the field remain unchanged or show a slight increase in temperature. Analysis of pressure data shows a minimum drawdown rate of 0.3 bars/year in the well field, and much higher drawdown rates in production wells. The production enthalpy of some wells that produce from shallow levels in the Momotombo reservoir, has changed from 1100 kJ/kg to almost a dry steam enthalpy, indicating that production from the field has reached peak capacity in some areas.