Simulation of reservoir behavior of the geothermal fields : Hamar, N-Iceland and Podhale, S-Poland

Abstract

The calibration of geothermal reservoir parameters and future predictions of its behaviour, based on a distributed parameter model, are the main parts of this report. In the first part, the Hamar geothermal field in N-Iceland is considered where measured and calculated water heads, silica concentration and reservoir temperature are fitted together. The monthly production from 1970 to 1991 is used in the calibration. After calibration, the future prediction of the reservoir behaviour was made, with different production rates, until the year 2006. A constant lowering of the water level is observed but with a tendency towards a semi-steady state if the production rate does not exceed 40 l/s. In the case of a constant pumping rate of 40 l/s, one can expect the drawdown in the year 2006 to be approximately 62 m. Future predictions of reservoir temperature indicate almost no changes within the next 15 years. The second part consists of the calculation of drawdown and temperature within a geothermal doublet, located in Podhale geothermal field, S-Poland, with production-injection rates of 20 l/s, 50 l/s and 100 l/s. The initial temperature of the production well is 86 C and after extraction of heat, in a heat exchanger, the water is cooled down to 30 C before it is injected back into the reservoir. The distance between the production well and the reinjection well is about 1200 m. The practical lifetime of a geothermal doublet, for a prescribed temperature drop of 3 C and for the above mentioned production-injection rates are respectively 220, 84 and 44 years of exploitation.