Tracer modelling and heat mining calculations for the Ahuachapán geothermal field, El Salvador C.A.

Abstract

Nine tracer test experiments using I131 and one using I 125 were carried out in the Ahuachapán geothermal field during 1987 to 1992. In only six of the tests some tracer recovery was reported ranging from 0.1% to 28% for individual wells. In order to obtain a one-dimensional fracture flow model estimate of reservoir geometry parameters, several simulations were carried out using the TRINV code for selected tests that show the higher tracer recovery values. The simulations provide a support for the conceptual reservoir model as the tracer velocities in the southern upflow zone of the field, are more than 10 times higher than when the tracer is injected in the north-east part, where colder downflow influences the reservoir. The results of the tracer simulations were used as input for simulating heat mining from the reservoir during long term injection. A reservoir parameters sensitivity study was carried out using different values of porosity, injection temperatures, formation temperatures, constant and variable injection flow rates, fracture thickness and height. Additional high pressure steam and additional thermal power recovery due to the injection were also estimated. In some cases the results show an unexpectedly high cooling of the reservoir even at short distances between injection and production wells ( 350 m). An electrical power recovery of 0.1 MW is estimated at lower injection flow rates (1-2 kg/s) of 160°C water.