Fiber-Optic Connectors: An Enabling Technology for High-Noise Subsea Environments
Authors: Awwad Shadi 
Published: October 2008

Ocean Design's Electro-Optical Wet-Mateable connectors have been used in the offshore industry since 1996. One of the most recent applications has been their use as an enabling technology in the development of next-generation subsea processing systems. Troll Pilot's subsea separation and water injection system, being developed by ABB Offshore Systems for Norsk Hydro is a recent example.

The separation and water injection system utilize a traditional gravity separator and a water injection pump operating at 2 MW. The system is to be located between a subsea gathering manifold and the Troll C platform. Separated oil is routed back to the platform, and wastewater is re-injected, either for pressure boost or into a disposal formation.

The demand to use optical fiber communication in this instance was driven by the need to reliably control the process systems in proximity to the high-power machinery located on the seafloor. The Electromagnetic Interference (EMI) generated by the high power, variable frequency drive to the injection pump/motor, can interfere with electrical communication systems, particularly where such a communication line is in the same umbilical as the power lines to the motor.

Fiber-optics offers a viable solution to communication problems caused by EMI, as optical fiber is inherently immune to EMI. In addition, the bandwidth advantage of optical fiber permits real time communication with the subsea control systems. Wet mate fiber-optic connectors permit the necessary modular installation of such a system.

This paper details the benefits associated with utilizing fiber-optics in subsea applications in general, and in subsea separation and water injection systems in particular. Some features of the wet-mate Electro-optical (hybrid) connector will also be discussed.

Introduction

Since Ocean Design's hybrid wet-mate connectors were made commercially available for the offshore industry in 1996, they have been used in a number of applications where conventional copper wire could not meet the needs for subsea communication.

As a result of these connectors, the technical communication advantages of optical fiber over electrical (copper) wire have become available to the offshore oil industry. These include large increases in bandwidth, increased repeaterless step out distance, improved harsh environment performance (downhole applications), and most importantly an inherent electrical noise immunity for systems that include high power or rotating machinery. Optical fiber also may provide significant cost advantage for some umbilical manufacturing and installation packages where its use may result in umbilical cross section reduction.

Electrical noise immunity has been a particular benefit in the Norwegian sector of the North Sea on the Norsk Hydro Troll Pilot separation program, the world's first full-scale trial of subsea separation and water injection system.

Background

Ocean Design Inc (ODI) first developed wet-mate hybrid connectors in association with Kvaerner Oilfield Products (KOP) for a European Commission THERMIE R&D program. The target of the program was to support the modular installation of a subsea fiber-optic communication system developed for applications such as the TOTAL Nautilus multiphase pump project. The Nautilus multi-phase project required high data rate and EMI immune communication for a tieback distance of 100 km.