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|The Challenges of Developing a Geothermal Ultrasonic Borehole Imager|
|Keywords: Geothermal, Borehole, Acoustic|
|Geothermal energy is the cleanest form of alternative energy, as it has the least environmental impact. The United States has vast untapped geothermal energy potential; using enhanced geothermal systems (EGS) technology, geothermal wells can supply the energy consumption for the USA for 2000 years. The Department of Energy (DOE) spearheads research and innovation in tools and technologies required for successful and economical use of EGS reservoirs. Temperature in some EGS reservoirs can exceed 300º C. This paper shall describe the development of a geothermal ultrasonic borehole imager rated to operate at 300º C. This borehole acoustic imager measures fracture patterns that convey information about the possibility of extracting heat by hot water/steam. Only if the rock is well fractured with continuous channels interconnecting large volumes of rock with a very large surface area is it possible to economically extract heat from the hole. Existing borehole imagers for oil and gas wells rely on one or a few sensors rotated in some fashion, such as by a motor or rotating mirror. Such technology is difficult to implement at high temperatures. An alternative approach is an azimuthal array of sensors that does not rely on moving parts. We shall address the development of piezoelectric sensors capable of working at 300º C. Literature on complete two-dimensional arrays of piezoelectric sensors is available. However, we shall explain how we can simplify to a one-dimensional azimuthal array to optimize manufacturability and performance. Electronics shall be housed in a flask where the temperature would be below 175º C. We shall outline electronics system design strategies to make the circuit functional at 175º C and above, specifically elaborating on power management, space utilization, sensor performance, and image quality (or fracture detection).|
|Kamalesh Chatterjee, Scientist