Engineered Reliability for Intelligent Well Systems
Authors: Veneruso Anthony F. , Kosmala Alexandre  G. , Bhavsar R. , Bernard Larry J. , Pecht Michael 
Published: October 2008

A new total-concept approach to achieving reliability for intelligent completion systems has produced successful installations in the BP Wytch Farm field and in the Norsk Hydro Troll and Oseberg fields. Intelligent monitoring and inflow-control systems optimize field production and ultimate recovery. Total reliability is critical to realizing these benefits. Reliability in all aspects of the completion, from equipment design to installation, is built into the engineering process. Reliability modeling and lifetime forecasts are based on system architecture; survival analysis is based on track records and accelerated testing of components. Modeling and forecasts are refined throughout the project to guide and accelerate design and development.

Introduction

Reliability of flow-control devices is a critical concern because, like permanent gauges, they are meant to last for the life of the well, yet they are not usually recovered for repair, maintenance or post-mortem failure analysis. However, whereas permanent monitoring systems have at least two decades of engineering evolution and field experience, downhole flow-control devices and the equipment associated with "intelligent wells" are relatively new since the first of such installations were made three years ago. These considerations make long-life field trials for new equipment impractical before commercial installation; therefore, identification of risks and reliability assessment through other techniques is essential. Industry initiatives by BP, Norsk Hydro, and others have stressed the importance of a structured approach to reliability and testing as part of the development process.1,2, 3

This paper addresses how the development of reliable intelligent wells can be accelerated to achieve the benefits they offer. The benefits of a total-concept approach to reliability have been demonstrated during the last three years in the development and field deployment of seventeen downhole flow control devices in twelve different wells, including the world's first all-electric system. The approach uses a mosaic of reliability and testing techniques. These combine analytical and experimental methods as part of the engineering development process from equipment design to field deployment and operation. These are described along with the benefits and limitations of each method.

Background

Recent studies have shown permanent gauge installations have achieved a 90%-5 year reliability for temperatures lower than 100°C, but this drops to about 50% in wells up to 150°C based on field track records for the past 6 years (Fig. 1).2,3 Detailed analysis of field track records shows that the cable and its connections cause the majority of failures. Therefore design improvements and reliability qualification testing (RQT) have focused on this area, especially since an electric cable and its connections provide the backbone for new-generation, electrically operated downhole intelligent completion valves and sensors.

Field experience with thousands of hydraulically operated subsurface safety valves has demonstrated their high reliability and long life. In addition they are cost effective and straightforward to install. However, an operational drawback of hydraulic valves is their limited flow control resolution, whereas an electric valve is infinitely adjustable over its openclosed range. Also an all-hydraulic system alone does not offer the possibility to provide downhole measurements of pressure, temperature and fluid flow rate.