Modelling of the Urridavatn low-temperature system in East Iceland

Abstract

The Urridavatn low-temperature geothermal system in East Iceland is located underneath Lake Urridavatn. It has been utilized for space heating since December 1979. A near-vertical fracture zone appears to control the flow of water in the system and a direct downflow of colder water from the lake has caused some cooling of water from production wells. A lumped parameter model and a detailed two-dimensional numerical model of the Urridavatn geothermal system have been developed. The lumped model consists of a single reservoir block which is separated from a very large, constant pressure reservoir by a leaky aquitard. The reservoir block is fed by recharge flow from depth. A new method is used, whereby the response of the lumped model to variable production can be calculated. The response of the lumped parameter model agrees well with the observed changes in temperature, chloride-content and water level. The two-dimensional numerical model is based on a conceptual model of the Urridavatn reservoir which, in turn, is based on available geological, hydrogeological, geophysical and chemical data. The physical processes considered in the model are mass transport, as well as conductive and convective heat transfer. The numerical model is calibrated by the observed changes in temperature and water level. Predictions of the future behaviour of the reservoir, through the two models, are presented for the three production wells.