Abstract

This paper presents the methodology and results from a major research project on well completion equipment reliability. Historical data were collected and analysed from a large number of installations represented by 17 participating oil companies.

The data were analysed using a purpose designed software package for reliability analysis (CERED). A standardized reliability data collection format was defined for the most critical items of downhole completions and implemented in this software package.

Generic and detailed reliability data are presented for entire completions as well as specific items, such as tubing, annulus safety systems, electrical submersible pumps and downhole permanent gauge systems. The paper also discusses the potential benefit of using reliability data as a decision basis, with consideration of limitations in data quality. The database established in this project represents nearly 800 completion equipment failures covering some 6600 well years of operation.

A separate database is established and maintained by SINTEF on Surface Controlled Subsurface Safety Valves (SCSSV). The paper also describes some long term trends in SCSSV reliability extracted from this database which now holds information on some 1400 failures. The latest update of this database was completed and reported in February 1992 as an integral part of the well completion study.

The cooperation with the participating oil companies and the major completion equipment manufacturers was instrumental in obtaining useful results in the study and is described in detail in the paper.

Introduction

The Ekofisk Bravo blowout in the Norwegian sector of the North Sea in April 1977 triggered a major research program into offshore safety in Norway, and was the direct reason for SINTEFs involvement in reliability studies of SCSSVS. From this point, these studies have been updated and expanded regularly, and the latest results are reported in IV. More recently, the scope of these studies was expanded to include also data on other well completion equipment /2/.

The objective of these studies has been to collect, analyze and process reliability data for vital completion equipment. The reliability data serve as a valuable decision basis for the oil companies, but also provides a unique source of feedback on performance for the downhole equipment manufacturers.

Collection of the reliability data has been possible only through close cooperation between the oil companies, manufacturers and SINTEF. The majority of data has been collected by staff members from the oil companies themselves using purpose made software and/or questionnaires. SINTEFs role has mainly been within software development, database implementation, quality assurance of data, manufacturer cooperation and processing of the reliability data. Use of dedicated software has been instrumental in achieving useful results from the studies.

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