Reservoir engineering studies in the Las Pailas geothermal field, Costa Rica

Abstract

The Instituto Costarricense de Electricidad (ICE) has, as part of its exploration strategy, carried out deep drilling in the Las Pailas geothermal field, located on the south flank of the Rincón de la Vieja volcano. This report includes an analysis of data related to reservoir engineering studies, obtained in the four wells drilled during 2001 and 2002. The data include downhole temperature and pressure profiles, injection, fall-off and discharge tests. The temperature and pressure logs permit estimation of reservoir temperatures and initial pressures, and simulation of dynamic conditions in two productive wells. Well parameters estimated a permeability range of 0.1-16.5 mD, the injectivity index varies from 1.5 to 13 l/s/bar and the productivity index range is 1.4-4.2 ? 10-12 m3, indicating good characteristics for commercial exploitation. The Las Pailas is a liquid dominated two-phase reservoir, with temperatures of 220-245?C and a drilled thickness of 600 m. The distribution of reservoir temperatures and pressures suggests that the heat source is located in the west part of the area studied and fluid flows are from west to northeast. The dominant mechanism for heat and fluid transport is fracturing, mainly toward the central part of the reservoir. Future exploration to quantify production conditions in Las Pailas, should focus on an area within a radius of 1 km of well PGP-01, mainly in a NW-SW direction.