| Abstract |
Olkaria geothermal field is an important source of reliable, cheap and environmentally friendly source of electricity in Kenya. It is a high temperature geothermal field located within the Kenya Rift system where the heat source is upwelling magma, coming near the surface through volcanic activity. Kenya electricity Generation Company (KenGen) is the main developer and operator of the field and it has been under exploitation for over 37 years. The company has also employed an early generation strategy by use of a wellhead technology in order to fast track geothermal development in Olkaria. Drilling operations are in progress to avail steam for installation of additional power plants. Furthermore, a feasibility study for an industrial park for supplying hot water and steam for industrial use is in the final stages of completion. It is therefore necessary that the geothermal resource in the field be developed and managed in an optimal, sustainable and environmentally friendly manner. This paper presents an updated numerical model of the Greater Olkaria geothermal system based on newly acquired data through the on-going drilling operations and production in the field. Numerical reservoir modeling is an important management tool, which has been used successfully in the past to guide decisions on exploitation and management of geothermal resources in Olkaria and other geothermal fields in the world. The research involved first updating the conceptual model based on all available reservoir and geo-scientific data and reports. The numerical model is then constructed based on the conceptual model by use of PetraSim, which is an interactive pre-processor, and post-processor for the TOUGH2. First, the natural state model calibration was carried out using the temperature and pressure data obtained in the field to establish the initial conditions of the reservoir before exploitation. Secondly, the initial state reservoir conditions and parameters were used as input for production model calibration. The results of the simulation study shows that a numerical model, which is a representative of the Olkaria geothermal reservoir, was set up and calibrated. The good match between the measured temperature and pressure data with the model-calculated values confirms this. The model was further refined based on the long-term production history and the pressure monitoring data. The model may be used to predict field performance under different exploitation scenarios as well as field development plans that may include reinjection and production strategy in the field. |