Reliability Testing Beyond Qualification of Downhole Electronics: Key Constituent in HP/HT Well Advancements
Authors: Balasubramanian Aswin , Flygare James , Shrivastava Pankaj 
Published: October 2017

Intelligent completion technology helps operators optimize life-of-well production, without costly intervention. Reliable and fit-for-purpose intelligent well systems help operators collect, transmit, and analyze downhole data, remotely control selected reservoir zones, and maximize reservoir efficiency during production. Permanently installed downhole electronics, instrumentation, and sensors are key features of any intelligent well system. Because these systems operate in severe downhole environments and are rarely retrieved to surface for analysis or maintenance, reliability testing beyond standard qualification testing is essential to achieve high operational reliability in high-pressure/high-temperature (HP/HT) scenarios. This paper presents the primary differences, benefits, and drawbacks of reliability test design techniques and describes an optimized approach to designing an integrated reliability test. It also highlights the importance of deriving a comprehensive reliability statement to meet performance guidelines during HP/HT operations.

Reliability tests can be broadly classified into test-to-failure and test-to-success categories. During test to failure, test specimens are run until failure occurs. Failure of a significant proportion of test specimens generates time-to-failure data, which are used to estimate system reliability. Whereas, test to success is set up as a success test; therefore, no failures are expected during testing. All test specimens should survive the designated amount of test time to demonstrate the minimum system reliability. The data obtained at the end of a reliability test are used to develop a product reliability statement. For HP/HT applications, a reliability statement should be measureable and associated with a failure definition. It should also incorporate a usage profile and specify the lifetime. The key elements of a comprehensive reliability statement are probability of success, associated confidence, operating conditions, and lifetime.

Reliability tests are primarily used to detect underlying design-based wear out failure mechanisms and latent production defects. A reliability test beyond standard qualification helps achieve overall system reliability by providing opportunities to help improve the design and production processes. These tests should be designed as a set of well-defined accelerated tests to help save product development time and meet the system reliability target for HP/HT applications. The conclusion of a reliability test leads to a comprehensive and meaningful product reliability definition.

This paper discusses the methodology and guidelines used to design an efficient reliability test for HP/HT applications. It also highlights the key input parameter control strategies for robust reliability testing. This paper presents the reliability test results integrated with a comprehensive reliability definition. A case history of an intelligent well system is presented to demonstrate the differences between the test-to-failure and test-to-success approaches, along with their advantages and disadvantages. The examples demonstrate how an efficient reliability test integrated with a comprehensive reliability definition can help lead to cost and time-to-market improvement for HP/HT well completion advancements.