Troll Pilot- Definition, Implementation and Experience
Authors: Horn Terje , Eriksen Gunnar , Bakke William 
Published: October 2008

In May 2000 Norsk Hydro reported, by means of an OTC paper, that Troll Pilot would be ready for start-up in June of that year. The Pilot was indeed started at that time. However, failures developed in the subsea installation briefly after startup. This triggered the Repair and Upgrade project, which is the subject of this paper. Troll Pilot Repair and Upgrade project had a time schedule of some 8 months and required a budget of approximately 15 million USD. It involved several interventions on the Troll Pilot subsea station during the summer of 2001.

Troll Pilot Definition

The object of Troll Pilot is to separate bulk water from the well stream and re-inject it from the subsea separator station, which comprises the following main components:–Separator vessel (liquid rate &gt; 60.000 bbl/D)–A water-injection pump (capacity &gt; 40.000 bbl/D)–Water injection well and associated tree

All of the above are incorporated into a structure that is separate from the subsea production-well templates.

Troll oil production is based on horizontal wells completed in a thin oil zone. It is an inherent feature of this mode of production that all the wells will produce at high water cut shortly after production start-up. Thus the requirements for water treatment on the two platforms Troll B and Troll C are considerable, and will, for most of the field life, set the limit on oil production.

It was recognized at an early stage of the Troll C platform development that any additional removal and subsea discharge of produced water would entail a corresponding increase in oil production.

Hence, the purposes of Troll Pilot were versatile, i.e.:Improve the water treatment capacity of the Troll C platform and its environment and thus the maximum throughputDemonstrate technical and commercial viability of subsea separation and boosting with a view to other applications.

Inherent qualities of "proven and accepted" technology for subsea processing solutions will result in benefits to future developments regarding;Environment and safetyIncreased recovery aspectsExpenditures.

The following features of Troll Pilot represent novel and new technology-elementsSubsea 3-phase separation11 kV, variable frequency power supply system for a remote single subsea loadIntegrated service umbilical for 5 function groups including optical fibers2 MW, 11 kV, wet make and break power connectorHigh bandwidth optical communication system for control of a subsea station2 MW subsea booster unitSubsea nucleonic level detection systemSubsea inductive level detection system

The high voltage power connector and electrical connectors for distribution of instrument power failed during the period June 2000 to December 2000. A repair program was initiated to rectify the failures. As of 25th August 2001 the Troll Pilot subsea station has been in regular operation with all referred new technical features successfully functioning as planned.

This paper documents the equipment failures, which triggered the Troll Pilot Repair and Upgrade project, the actions of the project and the results of the project efforts.