Evaluation of reservoir model predictions for the olkaria east geothermal field, kenya

Abstract

In 1984 a detailed three-dimensional well-by-well model was developed for the Olkaria geothermal field in Kenya. The model was calibrated against the production history of the field over the period 1977–1983, using porosity and permeability as adjustable parameters. During this period two 15-MW c Units were put on-line at Olkaria; the third 15 MW c Unit commenced operation in March, 1985. The numerical model was used to predict the performance of the Olkaria wells, and these predictions have been compared with the observed well behavior for the period 1984–1987. In general, the model predictions show satisfactory agreement with the observed well behavior, especially for those wells that had production histories exceeding two years. The predicted steam rates for most of the wells were accurate to within 1 kg/s for the period considered, and the steam rate decline was well-predicted by the model. Some differences between the observed and predicted total flow rates and enthalpies of individual wells were seen, especially in those wells with large enthalpy variations or unorthodox increases in total How rate. The model also predicted that three make-up wells would he needed by the end of 1987. which is consistent with the observed decline in total steam rates. New performance predictions have been made using an updated model, including the effects of wastewater reinjection.