A Complete High Integrity Overpressure Pipeline Protection System.
Authors: High G. , Loth W.D. 
Published: June 2014

Although most often associated with high-pressure production, a reliable system enabling subsea wells to be produced safety at long tie-back distances through flowlines rated to less than shut-in wellhead pressure offices cost savings for many developments. Previous work has shown that there is a sma/1 but finite probability of conventional flow control systems failing to shut off damaging overpressures. In most cases, this will arise from mechanical problems which are more likely causes than electronic failure within the production control system.

The proposed system provides a viable means of implementing a pressure specification break through the use of a modular, configurable system comprising four main components. T4e system is semi-autonomous, with dedicated pressure sensors and high integrity electronics being incorporated to avoid common mode system failures. Routine telemetry and reset capability would be conductedthrough the electro-hydraulic production control system.

The near-term availability of this protection system is an important consideration in justifying the economic viability of many marginal field developments.

1. Introduction

The capability to produce into pipelines rated for less than full wellhead shut-in pressure can lead tosubstantial savings in pipeline materials and installation costs, The most obvious savings may be made in high pressure systems where a combination of pressure and fluid properties demand very heavy wall pipe or duplex stainless material too thick to be welded with current technology, A less prominent but more common situation is lower pressure developments where reservoir pressures drop rapidly after a brief period of production but lines are designed for initial start-up conditions.

The high integrity overpressure protection system (HIOPS)is an important concept in facilitating this solution. This paper builds on some of the earliertheoretical work conducted by proposing a modular hardware solution using available technology, flexible enough to meet the requirements of current field scenarios, It should be stressed that this approach isput forward as one possible solution only, other methods may be appropriate according to specificfunctional requirements. Refs 1,2.

The configuration of the protection system is a complex problem. The wide variety of production scenarios, offsets, and fluid characteristics, means that differing requirements will be posed by many developments and the most cost effective system solution will at times consist of different elements of the complete system descibed in this paper, The main characteristics which distinguish potential IOPS applications areHigh wellhead shut-in pressure, typically &gt;5,000 psiExtended tie back to host Platform/facilities &gt;25Km

These two characteristics have a significant impact on the economic viability of a proposed development using conventional pipeline technology.

Under normal operating conditions the subsea production control system provides the necessary protection in the event of failure as a result of pressure build-up. Single valve failures will seldom lead to serious consequences. Most serious problems, however, are ascribed to mechanical rather than electronic components, These have involved crimped umbilicals, contaminated control luids, valves packed with hydrates or sand, orpressure transducers rendered inoperative by accumulations of paraffin or hydrates.