EGS : Framtidens Geotermiska System

Sammanfattning: The increasing demand for eco-friendly energy alternatives and the changing requirements of state of the art EGS-plants (Enhanced Geothermal Systems) have set the mark for many countries to start evaluating their geothermal assets. By using the EGS-technique, artificial reservoir providing district heating and electricity are created around the world by stimulating the bedrock hydrostatically with a process called hydroshearing. However, this technique has for long, been limited in cold thick bedrock by costly deep drillings. Interestingly, today´s fast development of the hydraulic hammer drilling technique has enabled a cost effective deep drilling to depths of six-seven km, even in crystalline bedrock and are, continuously being developed in Sweden as well as in South Korea, Germany and Australia. In this work I will present the EGS-technique and how the reservoir is formed. The technique is derived from hydrofracking for in which both methods and environmental risks have been valued against the ones of hydroshearing. The techniques are often combined and environmental friendly approaches are represented in both. Eight important geological parameters, affecting the potential of the EGS-plant have been determined. Granitic bedrock does respond well to these parameters, in case of homogeneous fracturing and increased levels of potassium, thorium and uranium, which results in high heat productivity. Four international pilot-projects, Pohang in South Korea, Newberry in USA, Soultz-sous-Forêts in France and Espoo in Finland are also presented in this work, with the Newberry and Soultz-sous-Forêts- projects as the main contributors in knowledge, especially regarding hydraulic stimulation of the bedrock. In the final part of this essay, a general presentation and assessment of the Swedish bedrock and it´s suitability for EGS-exploration is provided. The evaluation assessment is based on modern literature and data gathered from deep holes. Today´s best conditions are evaluated to exist in areas with sedimentary bedrock that connects to fracturing systems caused by impact- or fault structures. These conditions are found in the northwest of Scania, on Gotland and around the Siljanringen.