| Abstract |
In autumn 2014, the work on a borehole cooling-machine started and marked the next step in the development of the modular platform ZWERG for borehole tools, performed at the Karlsruhe Institute of Technology (KIT) within the last years. The project aims at the ready for operation development of a tool which allows the use of standard electronics, compatible with various measurement and interaction devices for borehole investigations in extreme environments. It includes an active cooling system as well as solutions for high pressure and corrosive surroundings. Therefore it provides optimal conditions for widespread borehole research. The project is part of a basic vision, a platform for fast and affordable borehole tool engineering, manifested in ZWERG, a long-term project containing concepts and ideas to fulfill nearly any borehole operation. This project is the core of several tool-development projects and offers solutions for basic problems with borehole temperatures, pressures and corrosive surrounding fluids by designing and searching standard components such as housings manufactured of nickel-based alloys, electronics usable with borehole-tool systems, cooling tools and others. The borehole cooling-machine bases on a concept to cool heat-sensitive components in borehole-probes, in high temperature environments, developed during a bachelor thesis, handed in at august 2011 at the KIT. This concept provides to use the compression refrigeration machine process, which is used in refrigerators, with custom designed components for the application in borehole environments. The process contains the sub processes evaporation, compression, condensation and expansion performed in the appropriate components. It is a reversible thermodynamic cycle process and therefore working without time limitations. The evaporator and the condenser, as well as different variants of expansion devices using capillaries or expansion orifices and valves are designed and manufactured in different version at the KIT to conduct experiments and optimize borehole prototypes; a prototype of the compressor for laboratory experiments has been manufactured, too. In further research activities the named components are tested in laboratory experiments conducting the complete cooling-process or sub processes with realistic conditions. For the adequate borehole design of the components, a widespread material research to identify materials with excellent mechanical properties and corrosion resistance at high temperatures and to develop techniques for processing and designing with these materials has been started. First outcomes can be seen exemplarily in the design of the cooling-system condenser. To further test the complete cooling-cycle at realistic conditions, a laboratory cycle is constructed where borehole conditions in depths of 5km with surrounding temperatures up to 200°C can be simulated. The used components are designed for the utilization in actual boreholes. A heat management ensures that the external temperatures are hold at the right values, sensors i.e. for temperature and pressure measurement help observing and controlling the process. The cycle is constructed in a way that different refrigerants can be tested as well as different surrounding conditions, representing different borehole depths. Over the following years, the cooling-system development shall be pushed forward through projects like COBOLD (Cooling of borehole objects in large depths) and GARM (Geothermal adjusted refrigerator module). The research efforts on the field of borehole-tool development will be continued and intensified in order to get closer to the declared target, to make investigation tools accessible and affordable for the broad geothermal research. Enabling it to do widespread borehole investigations will help the entire geothermal energy technology to become more efficient. |