Offshore/subsea systems

Designing Subsea Systems for Efficient Startup To Mitigate Topside Downtime

The workflow aims to reduce the startup time of a subsea production system (SPS). A dynamic integrated model is used to adjust the scheduled SPS startup time. The model evaluates the dynamic simulation response of a large field startup by integrating a reservoir- and gathering-network model.

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Introduction

The example presented in the paper focuses on a 29-well greenfield development in which the operator wanted to evaluate tying back the field to an aging facility. The operator determined that most of the repairs on the facility could be resolved within 4 hours. The field was planned to be designed for a 10-hour no-touch time, and the main concern was not related to the direct costs of repairs but rather to the hidden costs of lost and deferred production.

The task was to evaluate, in case of an unplanned shutdown caused by a topside equipment failure, whether it would be possible to start up all 29 wells on this field within a 6-hour window. The window is the time between the completion of the repair and the end of the no-touch time to avoid having to protect the field and incur additional costs and deferred production.

Because starting up a field is a dynamic problem that greatly depends on the reservoir conditions at the time of the startup, it was decided that it was critical to incorporate the reservoir model in this project and conduct a full integrated dynamic simulation that included both the production network and the reservoir model.

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