| Abstract |
Six distinct low-temperature geothermal systems, located in the Eyjafjördur region in N-Iceland, are utilized by Nordurorka for district heating of the town of Akureyri and surrounding regions. Five of these systems (Botn, Laugaland, Ytri-Tjarnir, Glerárdalur and Thelamörk) are of low productivity because of their size and geological setting, ranging from 15 to 45 kg/s in average production capacity (60 to 100°C resource temperature). The sixth system, Hjalteyri, which came on line at the end of 2003, is much more productive ( more than 250 kg/s of 90°C water on average). This blend of several systems of different capacity, along with the fact that production from many of the systems was often uncomfortably close to their capacity before Hjalteyri came on line, has required intricate resource management to be practiced. It has mainly included maintaining reservoir pressure above a certain level in each system and at the same time meeting the demand of the district heating system. Lumped parameter modelling of the pressure changes in all the geothermal systems, with associated future reservoir pressure predictions, has played a key role in this management. The lumped parameter models have been updated intermittently since they were first set up in 1988. The repeated modelling has proven to be a very effective resource management tool. Firstly by indicating how to limit production from the less productive systems and secondly by suggesting how much the other systems can additionally contribute. During the history of repeated modelling the capacity estimates for the different systems have either remained relatively unchanged or they have declined somewhat with time. In the case of Hjalteyri, however, the first model revision resulted in a capacity estimate that is 25% higher than the earlier one. |