| Title | The Development of the Seltjarnarnes Geothermal Field, SW Iceland During Thirty Years Production |
|---|---|
| Authors | Hrefna KristmannsdÛttir and Helga Tulinius |
| Year | 2000 |
| Conference | World Geothermal Congress |
| Keywords | Exploitation, development, geothermal field, changes, production characteristics |
| Abstract | The Seltjarnarnes geothermal field is situated within the town Seltjarnarnes, a suburb of ReykjavÌk, the capital city. Before drilling the first gradient wells there were no signs of geothermal activity in the area, but the thermal gradient exceeds 300 ?C/km. Subsequent drilling was successful, yielding 95-120 ?C hot water in ample quantities for the needs of the town in the foreseeable future. There are three main feedzones known in the geothermal field yielding 80-130 ?C hot water and possibly the fourth one with temperature exceeding 150 ?C. The field has proved to be rather complex with vertical as well as horizontal aquicludes. It was previously believed that the area was elongated along a NNE-SSW fault zone across the peninsula, but gradient wells drilled in 1995-1996 pointed to a circular main upflow zone located at the shoreline a few hundred meters to the north of the main area of exploitation. A new well subsequently drilled into the supposed main upflow yielded almost nothing by tests made before stimulation. However it opened up tremendously by pressure stimulation by injection packer and is now the best production well in the field. Subsequently the other wells have been cooled and their production characteristics altered. When the wells were first produced the water was found to be somewhat saline (<1â salinity) and the salinity increased with time and production rate causing severe corrosion problems. Almost no changes were observed in chemistry of the waters during the first 5-6 years of exploitation. Then the salinity started to rise at a slow speed during the subsequent 4- 5 years to 1983 and then sharply during 1983-1986. The speed of increase then slowed off and finally almost stopped due to measures taken to reduce production from the field. The best production well has the most saline water probably due to increased circulation in the middle of the upflow zone. There has not been any cooling of the reservoir due to seawater inflow, but the production characteristics have changed. Thus supersaturation of calcium carbonate has increased substantially, but no scaling has happened sofar. The increase in production from the area has been close to what was forecasted in 1995 and the regional drawdow similar as forseen. The drawdown of the last well drilled in the supposed main upflow zone is much less than expected and the production larger. |