Thermal Conductivity Performance and Insulation Benefits of Steel and Titanium Hybrid Drilling and Production Strings for Geothermal Wells

Abstract

This paper presents an ASTM based thermal conductivity testing program for bare titanium Grade 5 and coated pipe materials intended for high temperature or super-hot rock geothermal drilling and production. Measurements between 120°C and 500°C using two standardized methods provide a consistent dataset of apparent thermal conductivity and thermal resistance under controlled laboratory conditions. The results show that thermal barrier coatings can significantly reduce heat transfer through the drill pipe wall compared with bare titanium and coated titanium and steel, with one advanced coating achieving particularly low conductivity over its qualified temperature range. By comparing the two test methods, the study clarifies when each is best applied using D5470-17R24 as the primary standard for coated systems and E1225-25 as a complementary method for uniformed materials (i.e. bare metals) and high temperatures. The resulting dataset and ing protocol are intended for direct integration into wellbore thermal models and hybrid drill string and production casing / tubing design workflows, enabling more accurate prediction of internal fluid temperatures and supporting strategic placement of titanium, coated titanium, and coated steel sections along the drill string in superhot geothermal wells. This dataset and protocol can effectively support casing and production design processes.