Research on the Thermal Insulation and Cooling Performance of Insulated Drill Pipe

In geothermal and dry hot rock drilling, the reliability and safety of downhole tools and instruments are significantly affected by high temperature downhole environment. Insulated drill pipe (IDP) can be used to reduce the bottom hole circulating temperature (BHCT) and solve technical problems caused by high temperatures. To validate its thermal insulation and cooling performance, relevant researches were conducted by combining experiments and theoretical analysis. First, an experimental test bench and principle verification drill pipes for testing the thermal insulation performance of IDP were developed. Then, comparative testing and analysis were conducted between IDP and conventional drill pipe (CDP). Finally, taking the drilling data of a well as an example, the ability of IDP to reduce BHCT was analyzed. Results indicate that, the overall heat transfer coefficient (OHTC) between the inner and outer walls of the IDP is reduced by 95.4% compared to CDP. This reduction blocks about 93.7% of the heat transfer between the drill pipe bore and the annulus in the experiments and achieves a 58.8℃ reduction in BHCT compared to CDP in a calculation example of a well.The thermal insulation and cooling performance of IDP is remarkable. The IDP can provide a safe temperature environment for downhole tools and instruments, and has good application prospects in geothermal or dry hot rock drilling.