Designs for reliability and failure mode prevention of electrical feedthroughs in integrated downhole logging tools

Abstract

Abstract To enable an electrical feedthrough integrated downhole logging tool to maintain high reliability during its logging service in any hostile wellbores, it is critical to apply some guidelines for the electrical feedthrough designs. This paper introduces a safety factor based design guideline to ensure an integrated electrical feedthrough has sufficient compression or thermo-mechanical stress amplitude in the stress well against potential logging failures. It is preferred to have a safety actor of 1.5~2.0 for an electrical feedthrough at lowest temperature, such as −60°C, and a safety actor of 2.5~5.0 at operating temperature range of 200~260°C. Moreover, the designed ambient pressure capability should be 1.5~2.0 times higher than the maximum downhole pressure, such as 25,000~30,000PSI. To validate this thermo-mechanical stress model, several electrical feedthrough prototypes have been tested under simulated 200~260°C and 31,000~34,000PSI downhole conditions. The observed testing data have demonstrated that there is a maximum allowable operating pressure for an electrical feedthrough operating at a specific downhole temperature. It is clearly demonstrated that an electrical feedthrough may operate up to 60,000 PSI at ambient temperature in a real life application, but it may actually operate up to 30,000~35,000 PSI at 200~260°C downhole temperatures.