Design for Reliability in Downhole Control Systems
Abstract: A reliable downhole flow-control system is essential for any intelligent completion. Generally, systems that meet the sought-after criteria are installed permanently in severe downhole environments and are not expected to be retrieved for analysis or maintenance despite harsh conditions. The entire system must achieve high operational reliability at temperatures as high as 200° C and pressures that reach 30,000 psi. This paper discusses the electro-hydraulic module of a reliable control system, … Show more
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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.
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.
A Streamlined Product Development Process for Permanent Downhole Gauge: Key to High Operational Reliability in HPHT Wells
A permanent downhole gauge (PDG) in an intelligent completion provides real-time data concerning downhole conditions that can be used to assess the well environment and make informed decisions regarding reservoir and well integrity management. These gauges are permanently installed in severe downhole environments and rarely retrieved to surface for analysis or maintenance. Despite harsh conditions, the gauge is designed to achieve high operational reliability at temperatures of up to 200°C and pressures that reach 30,000 psi. The scope of this paper includes successful application of design for reliability (DfR) principles to streamline the product development process for high-pressure/high-temperature (HP/HT) environments. Equipment and material reliability is critical to success in HP/HT environments. This paper discusses a reliability focused product development approach and highlights the application of DfR techniques used to qualify a downhole gauge for an operator's prelude floating liquefied natural gas (FLNG) project offshore northwestern Australia. In this major well development project, downhole gauges are used for real-time permanent monitoring at high temperature downhole conditions. High operational reliability of a downhole gauge is important to ensure functionality throughout facility commissioning, startup, and operations after a well suspension period. Reliable recording of well integrity data during the well suspension period also helps improve operational simplicity. The DfR process is a systematic, streamlined, and concurrent engineering program designed to meet system reliability targets. This paper examines establishing a reliability specification for a downhole gauge, managing design risk using design failure mode and effect analysis (FMEA) followed by design robustness testing using highly accelerated life tests, leading to a reliability demonstration test program to achieve target system reliability. This paper highlights an application of optimized DfR strategy along with an efficient reliability qualification test that resulted in successful product development. Improvements to the quality process to ensure reliability consistency between testing and the final commercial deployed gauges are also addressed in this paper. Additionally, this paper highlights strategic application of a powerful DfR process that aided design de-risking and helped attain system reliability targets, thereby, helping the operator meet its needs. Also demonstrated is how an efficient DfR process led to streamlined product development of a permanently installed downhole gauge resulting in cost and time-to-market improvements while establishing reliability.
A Novel Approach to Reliability Qualification Testing: Key Constituent in Successful Development of Electrohydraulic Flow Control Device
Flow control devices (FCD) play a vital role in an intelligent completion’s ability to enhance reservoir management capabilities by allowing the operator to control inflow and outflowremotely. Among FCDs, the most versatile type is electrohydraulic. However, because these electrohydraulic FCDs are permanently installed in severe downhole conditions, it is important to integrate the reliability qualification testing (RQT) in the overall development effort. This paper describes a novel approach to product development which integrates RQT as a key component. RQT incorporates testing for all criteria, including function, environment, and reliability. It typically includes accelerated testing, which is performed to reduce testing time while helping ensure product reliability is verified. RQT is applied in the form of a systematic, streamlined, and concurrent verification program to help improve the reliability of the product. Design for reliability (DFR) tools, such as FMEA (failure mode and effects analysis), help identify the key failure modes and failure mechanisms (causes of failure) related to the product. It is of utmost importance to understand these failure mechanisms in detail and correlate them to the stresses applied during testing. RQT planning uses the analyses performed during the design phase, such as FMEA, reliability predictions anddevelopmenttesting results, to highlight the risks associated with the product. And, further integrates this information to efficiently design the tests. The primaryobjective of RQT is to determine whether the product will meet the mission reliability target. RQT planning not only identifies the need for component reliability testing, but also substantiates reliability targets at the component level. Multiple ingredientsare required todevelop an efficient RQT, such as (a) performing risk-mitigation studies during design phase, (b) defining a mission reliability target at the system and component level, (c) addressing the range of environmental conditions, (d) using accelerated test plans, (e) optimizing test parameters, sample size, test time, etc. This paper presents an efficient RQT plan, developed for FCD, as well as all associated accelerated testing models for system reliability predictionsand statistical confidence. Also discussed is a uniqueapproach for identifying and integrating key elements of a holistic RQT, which can be used to design an efficient test plan. This approach unites the reliability studies performed during development stages, and further, uses accelerated testing for successful product development, resulting in both cost and time-to-market improvements.
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