Characterizing geothermal wells and their surrounding geothermal formations requires the use of electronic subsurface logging tools that monitor conditions (e.g. temperature, pressure, flow, fluid chemistry); unfortunately, few electronics can gather and transmit accurate data at temperatures exceeding 200 ˚C. The most common workaround is to place a low temperature electronic device inside a vacuum flask, which slows the migration of heat transfer from the surrounding rock formation, but the drawback to this approach is that the tool is limited to a few hours of operation before it needs to be removed from the geothermal well. Enhanced geothermal systems require long-term characterization, with tools and downhole monitoring systems that can be emplaced for months at a time. At Sandia National Laboratories, the Geothermal Department is focused on developing subsurface tools that can operate for a month or more at temperatures reaching 300 ˚C. At present, we are developing a range of electronic packaging techniques that integrate off-the-shelf high-temperature surface mount integrated circuits onto ceramic printed circuit boards, with gold-tin solder and wire bonding, along with a conformal coating to improve reliability. These four-packaging techniques have been evaluated at 300 ˚C towards the goal of demonstrating a 300 ˚C datalink that uses a RelChip RC10001 microcontroller for geothermal well evaluation.
Wright et al. (Tue,) studied this question.