Transmissivity (kh) Determination in the Miravalles Geothermal Field, Costa Rica

Abstract

The Miravalles Geothermal Field is located in the north-west part of Costa Rica. Miravalles has been producing electricity since 1994, nowadays it is producing 142 MWe, in three condensing units and one back-pressure unit. Miravalles has a liquid-dominated, two-phase reservoir, with temperatures of 220-250 ?C.
This report includes an analysis of the data related to reservoir engineering studies, obtained in transient pressure tests carried out in 23 wells out of 54 drilled since 1979. The data were obtained in injectivity tests during completion and include determination of transmissivity, using the semilog and the type-curve methods.
Estimated well parameters shows a wide variation indicating different reservoir conditions. Transmissivity varies between 0.22 and 77.9 Dm. It is possible to define two regional trends in NE-SW, N-S orientation, with higher values in some wells of the north zone of the field and also, with higher relative values for wells located in the peripheral area, compared with the central field zone. The structural conditions represent an important factor for the parameter determined, indicating a good correlation with the structural characteristics defined in Miravalles.