Analytical Approach to Selecting and Designing a Miniature Downhole Refrigerator

The design approach and results from a series of analyses used to select a miniature high-temperature multi-watt refrigerator for thermally protecting downhole instruments are described. Thirty-one systems from nine physical or chemical processes were investigated and compared against the design criteria and constraints. Preliminary thermodynamic analyses and the results of a search for high-temperature components and refrigerants eliminated all but three processes and seven systems. These seven systems were re-evaluated based on a set of proposed design changes that reflect natural evolution from a prototype to commercial system application. Final selection considered refrigerator interactions with the geothermal logging system to define failure modes, ensure compatibility, and allow adaptability to changing conditions. The selected refrigerator design permits reliable, long-term active cooling of downhole instruments in hot wells. The consistent design, systematic analysis and unbiased selection process represent a new body of research results that provide potential for substantial advances in downhole thermal protection technology.