Soft stimulation treatment of geothermal well RV-43 to meet the growing heat demand of Reykjavik

Santiago Aldaz,Vala Hjörleifsdóttir,Günter Zimmermann,Francesco Grigoli,Torsten Dahm,Bjarni Reyr Kristjánsson,Stefan Wiemer,Marco Broccardo,Arno Zang,Simona Regenspurg,Hannes Hofmann,Dimitrios Karvounis,Claus Milkereit,Gylfi Páll Hersir,Ernst Huenges,Sebastian Heimann,Sigurveig Árnadóttir,Ragnheiður St Ásgeirsdóttir,Rögnvaldur Magnússon

doi:10.1016/j.geothermics.2021.102146

Abstract

Reykjavik is almost entirely heated by geothermal energy. Yet, recent growth of the city significantly increased the heat demand. Past experiences in Iceland's capital region showed that hydraulic stimulation of existing geothermal wells is suited to improve hydraulic performance and energy supply. However, fluid injection may also trigger felt or even damaging earthquakes, which are of concern in populated areas and pose a significant risk to stimulation operations. Consequently, soft stimulation concepts have been developed to increase geothermal well performance while minimizing environmental effects such as induced seismicity. In a demonstration project of hydraulic soft stimulation in October 2019, more than 20.000 m³ of water were injected into well RV-43 in Reykjavik in multiple stages and with different injection schemes. The hydraulic performance of the well was improved without inducing felt seismicity. An a priori seismic risk assessment was conducted and for the first time the risk was continuously updated by an adaptive traffic light system supported by a sophisticated realtime microseismic monitoring. Our results confirm that it is possible to improve the performance of geothermal wells in Reykjavik and worldwide with acceptable technical, economic, and environmental risks. Here we provide an overview of the entire stimulation project including site description, stimulation design, zonal isolation, logging, seismic risk assessment and mitigation measures, realtime seismic, hydraulic and chemical monitoring, and stimulation results and challenges.

Highlights

Geothermal energy provides 99.9% of the district heating load of Reykjavik, the capital city of Iceland (Gunnlaugsson et al, 2000)
Future stimulation treatments in the area will greatly benefit from the experiences gained by the RV-43 stimula tion experiments
Due to the vicinity of the well to the city center of Reykjavik, special emphasis was given on seismic risk assessment and mitigation

Summary

Introduction

Geothermal energy provides 99.9% of the district heating load of Reykjavik, the capital city of Iceland (Gunnlaugsson et al, 2000). This energy is distributed through two separate networks. One network is fed by the two high temperature power plants Nesjavellir and Hellisheiði located ~20–30 km east of Reykjavik. The second network is fed by the three low temperature fields Laugarnes, Ellidaar, and Mosfellsbær located within or near the city limits. While the operator Reykjavik Energy considers both, drilling and stimulation, the demonstration of a safe and reliable method for hydraulic stimulation as productivity enhancement technique for Reykjavik is subject of this study. The ~1.55 km deep and 1.82 km long well RV-43 on the peninsula Geldinganes was chosen as representative demonstration site

Results

Discussion

Conclusion