Effective Solutions For Subsea Developments Over Existing North Sea Installations
Authors: Roberts Brian 
Published: October 2008

Currently given the economic situation in the developed world of low energy prices plus high capital and labour costs any modifications to Operational platforms have to be justified against these harsh economic criteria. The challenge to any project team is to formulate a strategy whereby new field developments or platform debottlenecking is implemented by innovative and effective engineering. The major problems which need to be resolved when modifying an existing platform are:Is new separation equipment required?Is the oil evacuation system large enough to export the new oil flowrates?Is the existing compression system adequate to handle the new gas flowrates?Is the existing produced water system capable of handling the new flowrates?Are the utility systems adequate to cope with the new throughputs?Is enough space available to install the new equipment?

This paper describes how two separate projects tackled these problems.

The first example highlights how a simple modification to the cooler system on a 1st generation platform led to the throughput of the platform being increased to 150% of the original design figure. The second shows how by using the following approach a 2nd generation platform was debottlenecked. The throughput of the platform was increased from 80,000 bpd to 195,000 bpd, whilst the original idea of using an additional stand alone processing module was abandoned in favour of integrating the equipment required to develop the new subsea field into the existing platform infrastructure. This approach led to a cost saving of £40 M and also allowed the project to be completed on schedule.Checks should be carried out on the existing separator sizes, using realistic calculation procedures and an offshore trial.Hydrocyclones should be considered for any debottlenecking exercise.On platforms which have not been specifically designed for gas export, both low pressure wet gas export and high pressure gas export can be considered. Depending on the relative price between oil and gas, NGL recovery schemes should be evaluated as they can result in potential increased revenue.The use of new space saving equipment eg Printed Circuit Heat Exchangers or Multi-Phase Meters should be considered wherever possible.Detailed checks should be carried out on utility systems as these often turn out to be the major problem area when debottlenecking a platform.

All of the modifications outlined in the paper have been successfully implemented.

Introduction

The aim of this paper is to outline the opportunities which become available during either the addition of a new subsea development or the debottlenecking of the existing facilities on a UK North Sea oil production platform. The paper outlines the technology applied to two examples, the first being the debottlenecking of a first generation platform, the second being the development of a new subsea field which was to be tied back across an existing second generation platform. In both cases innovative engineering solutions, including the application of new technology were applied to the problems presented at the outset of the projects.