Exploitation of super-critical water from deep geothermal resources can potentially give a 5–10 fold increase in the power output per well. Such an improvement represents a significant reduction in investment costs for deep geothermal energy projects, thus improving their competitiveness. The ongoing European Horizon2020 DESCRAMBLE (Drilling in dEep, Super-CRitical AMBients of continental Europe) project will demonstrate the drilling of a deep geothermal well with super-critical conditions (>374°C, >220 bar) by extending an existing well to a depth of around 3.5km. The drilling operation is depending on verification of the bottom hole pressure and temperature where state-of-the-art electronic logging tools cannot operate reliably. SINTEF has developed a novel pressure and temperature logging tool for this extreme environment. The target specification for the tool is 8 hours logging of temperature and pressure at 450°C and 450 bar.
In this work, we describe the tool requirements and discuss the design choices made with emphasis on the electronics platform and limitations imposed by the available battery technology, as well as the casing and heat shielding. Test results of the tool are presented, including test data from a field-test in a 250°C geothermal well in Larderello, Italy.