PREDICTING FUTURE PERFORMANCE OF A SHALLOW STEAM-ZONEIN THE SVARTSENGI GEOTHERMAL FIELD, ICELAND

Abstract

As a part of a feasibility study for adding new 30 MWe unit to the Svartsengi Power Plant, a simple reservoir model study has been carried out. The model concentrates on a shallow, production induced steam-zone which now resides at 200-700 m depth. Only 1-D vertical mass flow is assumed in the upper part of the model, and only horizontal radial flow in a base layer, extending 9 km out. The model simulates some key figures in the production history, such as deep and shallow reservoir pressures, enthalpy changes in steam wells and increasing steam flow to surface with time. The study indicates that during the first 15 years of production a substantial mass of fluid was pushed by steam expansion into the deeper, liquid dominated reservoir layer. However, as production declined recently, a rapid liquid backflow tock place into the already 500 m thick steam zone, hence reducing it's volume and production capacity. Modeling various future production scenarios suggests that the deep reservoir pressure should stay constant or even decrease continuously with time. This will maximize the steam production from the shallow, man made steam zone.