Preliminary Reservoir Engineering Studies 0 F the Miravalles Geothermal Field , Costa Rica

The Earth Sciences Division of Lawrence Berkeley Laboratory in cooperation with the Instituto Costarricense. de Electricidad is conducting a reservoir engineering study of the Miravalles geothermal field, Costa Rica. Using data from eight exploration wells, a two-dimensional areal, natural-state model of Miravalles has been developed. The model was calibrated by fitting the observed temperature and pressure distributions and requires a geothermal upflow zone in the northern part of the field, associated with the Miravalles volcano and an outflow towards the south. The total hot (about 260OC) water recharge is 130 kgk, corresponding to a thermal input of about 150 MWt. On the basis of the natural-state model a twodimensional exploitation model was developed. The field has a production area of about 10 !a2, with temperatures exceeding 220OC. The model indicated that power generation of 55 MWe can be maintained for 30 years, with or without injection of the separated geothermal brine. Generation of 110 MWe could be problematic. Until more information becomes available on the areal extent of the field and the properties of the reservoir rocks, especially their relative permeability characteristics, it is difficult to ascertain if 110 MWe can be sustained during a 30-year period.