Design for Reliability in Downhole Control Systems

Abstract

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, which optimizes reservoir performance and enhances reservoir management capabilities by allowing the operator to remotely control the wellbore and obtain real time sensor data (which includes pressure/temperature). In order to meet the necessary system reliability targets, a Design for Reliability (DfR) process is applied in the form of a systematic, streamlined, and concurrent engineering program to assess the system's capabilities. A DfR is considered to be an integrated process rather than a step task for the design and development of the electro-hydraulic control module. The DfR process identifies the utility of reliability engineering tools and methods during the product development cycle. The objective of DfR is to meet the reliability expectations and optimize the overall life-cycle costs. This paper discusses the methods and tools of DfR and highlights the successful application of key DfR tools and techniques in the development of the electro-hydraulic control module. A variety of reliability tools were applied in the development cycle which includes (a) reliability requirements and flow down, (b) reliability block diagram for system reliability modelling, (c) design FMEA (failure mode and effect analysis) for design-based risk assessment, (d) baseline predictive reliability modelling, and (e) reliability qualification test design. This paper will focus on how to apply the DfR process in the product development. It will also highlight the process steps required to make DfR a powerful and effective process that can help any organization design reliability into its products. The DfR process can be applied efficiently by taking the strengths and limitations of its tools into consideration. In order to enable an effective and efficient application of the DfR process, the order in which various reliability engineering tools are applied is important.