Abstract
Geothermal power generates electricity using steam as coal, oil and nuclear powers, but the power is based on natural energy as hydraulic, sunlight and wind powers being meteoric and originating in solar energy. Generally, most powers based on meteoric energy fluctuate hour by hour. In contrast, hydraulic power, though it is also meteoric, is relatively constant, because a water reservoir is prepared. Geothermal power also stores in a reservoir. In this sense, geothermal power is the same as hydraulic power. A geothermal reservoir model has many uncertainties caused by estimation errors of geophysical properties such as temperature, permeability and others. A reservoir simulator has also its own uncertainty as a facility of chemical analysis. After a geothermal field is developed, many processes happening in the reservoir will be stochastic. In order to reduce risks accompanying geothermal development and to optimize the development, we should establish an assessment technique which takes account of these uncertainties and stochastic processes.
