The development of measurement while drilling (MWD) and logging while drilling (LWD) tools for highly efficient directional drilling operations warrants the development of extended control and better sensing capabilities in the drilling tools. A direct consequence of these requirements is the increased use of electronic devices with high power dissipation rates, along with an increased device density in the various components of borehole assemblies (BHA). With the operating environment of such tools already very harsh (i.e., ambient temperatures of approximately 175°C and pressures of 25,000 psi), it is critical to ensure the implementation of effective thermal management techniques to prolong the life of the electronic devices.
This paper identifies the bottlenecks and assesses their effect on the thermal transport process in one of the components of a BHA. A combination of numerical computation and experimental approach has been undertaken for this study to identify the areas for improvement to develop efficient thermal management solutions in the LWD and MWD tools. The experiments are conducted at controlled boundary conditions, and FEA-based numerical models are developed to simulate the experiments. The numerical results show an excellent match with the experimental measurements, thus validating the developed numerical model and the associated assumptions.
Based on the experimental observations, a model design analysis method, using the numerical model, is presented to assess the sensitivity of the thermal performance of the electronics to the variation of multiple parameters identified as having an effect on the heat transfer characteristics. The study shows that the junction temperature of the electronic devices is more sensitive to the thermal conductivity of the thermal plate when compared to the convective heat transfer coefficient of the test fluid. This is caused by the difference in the relative thermal resistance offered by the various components in the assembly. In addition, a parametric design study was performed to illustrate the effect of some of the important parameters that contribute to the overall thermal resistance in the tool, thereby affecting the junction temperature of the electronics. The thermal conductivities of the thermal plate and the insert were found to have the greatest effect on the thermal response of the electronics to different boundary conditions.
The findings from this work demonstrate the significance of developing a thorough understanding of the different aspects of the design of drilling tools regarding their effect on thermal management. Considering the harsh environments in which the drilling tools usually operate and the various effects of a malfunction of such tools, an optimized thermal management strategy is highly critical to ensure the reliability of their operation. This work attempts to identify the major bottlenecks for efficient thermal transport in drilling tools and provides a baseline framework for design methods that should be considered for developing optimized thermal management solutions.
