Ensuring Operability and Availability of Complex Deepwater Subsea Installations: A Case Study
Authors: Langli G. , Masdal S.I. , Nyhavn F. , Carlsen I.M. 
Published: October 2008

This paper addresses the use of RAM (Reliability, Availability and Maintainability) and logistics analyses in the design phase of complex deepwater subsea installations. A model for conducting such analyses has been defined and applied to a case. Results, observations and experiences are presented. The main conclusion is that the performance of such analyses is crucial for achieving the required regularity requirement of complex deepwater subsea installations.

Introduction

Reliability, or the lack of such, can severely affect the operability, availability and hence the overall economics of an offshore oil & gas installation. The oil & gas industry provides examples on success stories and some less successful stories. In some cases the main cause of the problem is related to the reservoir - or lack of technology and knowledge to manage the reservoir and well flows. In other cases the problem is related to the design, e.g. new technology and equipment, new materials, or simply that the design & engineering did not manage to identify potential hazards and operational challenges.

The accumulated experience of the oil & gas industry is enormous, and much of this experience is mirrored in the numerous design standards and specifications. However, when it comes to systemization of operational experience in the form of e.g. reliability databases, both availability and applicability of operational experience are restricted.

The accelerating development in definition and execution of offshore and subsea oil & gas field developments, and the increased pace in technological development, challenge the application of experience and operational data. This is in particular true for subsea field developments in deepwater and ultra deep waters.

This paper presents a review of the approach to and major results of the design of a fictive deepwater subsea field development, with emphasis on operability and availability. The Fictive Field is located on the Norwegian Continental Shelf (NCS) in some 850 meters of water. Due to reservoir and formation characteristics, and to minimize the hazards of hydrate formation and scaling, the use of novel technology and technology with little field experience was considered necessary. This, combined with the location and water depth, made it necessary to investigate supportability of the well system and subsea installations.

A model for inter-linking Reliability, Availability and Maintainability (RAM) analysis and analysis of logistics was developed to aid the design in the identification of the obvious and the less obvious technical and operational challenges for a field development of this type. The analyses make use of operational data and reliability data, and where such data is missing, actions were taken to establish data using expert judgements, and to determine the impacts on the design and the operational support from uncertainties in the data.

The Field

The Fictive Field is located on the NCS in some 850 meters of water. The field extends over four fault blocks, separated by faults. The total area is approximately 40 km2. The recoverable reserves are estimated to 60 billion Sm3 of oil.