Jules Verne or Joint Venture? Investigation of a Novel Concept for Deep Geothermal Energy Extraction

Abstract: Geothermal energy is an energy source with potential to supply mankind with both heat and electricity in nearly unlimited amounts. Despite this potential geothermal energy is not often considered in the general energy debate, often due to the perception that it is a margin energy source bound to a few locations with favorable geological conditions. Today, new technology and system concepts are under development with the potential to extract geothermal energy almost anywhere at commercial rates. The goal of these new technologies is the same, to harness the heat stored in the crystalline bedrock available all over the world at sufficient depth. To achieve this goal two major problems need to be solved: (1) access to the depths where the heat resource is located and (2) creation of heat transferring surfaces and fluid circulation paths for energy extraction. In this thesis a novel concept and method for both access and extraction of geothermal energy is investigated. The concept investigated is based on the earlier suggested idea of using a main access shaft instead of conventional surface drilling to access the geothermal resource, and the idea of using mechanically constructed 'artificial fractures' instead of the commonly used hydraulic fracturing process for creation of heat extraction systems. In this thesis a specific method for construction of such suggested mechanically constructed heat transfer surfaces is investigated. The method investigated is the use of diamond wire cutting technology, commonly used in stone quarries. To examine the concept two heat transfer models were created to represent the energy extraction system: an analytical model based on previous research and a numerical model developed in a finite element analysis software. The models were used to assess the energy production potential of the extraction system. To assess the construction cost two cost models were developed to represent the mechanical construction method. By comparison of the energy production potential results from the heat transfer models with the cost results from the construction models a basic assessment of the heat extraction system was made. The calculations presented in this thesis indicate that basic conditions for economic feasibility could exist for the investigated heat extraction system.