The behaviour of drilling and production risers is normally predicted through mathematical analysis and modelling. These methods can be of varying accuracy and give different levels of confidence in the riser performance predicted. Mathematical analysis can be supported and validated by monitoring the dynamic response of risers in service.

This paper outlines various options for remote monitoring and data recovery and describes the design and development of BP's Universal Stress Monitoring Equipment (USME) The USME is a subsea data acquisition system that enables data from remote sensors to be collected, processed and stored subsea. Data is retrieved to the surface via a high speed acoustic link.

The equipment was first deployed on the Buchan floating production rig in 1987. It was then upgraded and tested in 1000 metres water depth before being deployed during the drilling of a deep water well west of Shetland in 1989 The practical operating experience and results from these trials is described and further potential applications are discussed.

INTRODUCTION

In order to improve the confidence in computerised mathematical model input data for tensioned risers, BP has carried out several stress monitoring exercises and has developed new equipment and techniques for remote monitoring applications

Background

In 1985 a stress monitoring exercise was carried out on the export and production risers of the Buchan Alpha floating production system A conventional hard wire data acquisition system was used with sensors clamped onto the export riser and hard wired through the moonpool area. The exercise was successful and yielded high quality data which have been used to extend Buchan's environmental operating envelope However, this system was designed specifically for Buchan and could not be readily deployed elsewhere A hard wired system was considered to be impractical for deep water applications due to the difficulties of running the wires over long distances and resultant high risk of signal loss

In order to overcome these problems, BP initiated a programme for the development of a reusable remote monitoring system. This system was designed to collect subsea data from a variety of inputs and transmit it to the surface at high speed via a hydro-acoustic link.

Techniques

There are many options available in the development of a remote monitoring system. The fundamental decisions are in the type of data link, whether to store data subsea or at the surface and the design of the transducers

The data link between the subsea installation and the surface can be either hardwired, acoustic, optical fibre or possibly hydraulic. A hardwire link can use a dedicated piggy-back cable or spare cores within a control umbilical. Previous experience with hardwire failures and the long installation time required for a deep water application suggest that acoustic communication is more appropriate for a universal system than any direct link Optical fibres and hydraulic lines are as prone to failure as electrical cables An acoustic link offers greater flexibility and adaptability as it is possible to receive data from a number of different subsea locations. The main disadvantage of this arrangement is that power must be supplied by subsea batteries This limits the total volume of data that can be recovered before battery change out is required

Subsea data storage avoids the need for constant communication but may exceed practical limitations on the space available. This problem can be alleviated, if not eliminated, by having subsea processing capability. Data can then be reduced to provide the required statistical results without

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