The oil industry suffered a severe set-back as result of the accident in the Gulf of Mexico in 2009, which showed clearly the public awareness and environmental aspects related to such accidents. A concept based on subsea tunnels and caverns has been developed for an offshore oil field in Northern Norway as alternative to traditional development strategies for offshore oil fields. The concept includes 2 or 3 parallel tunnels descending from an onshore terminal facility to a base station at the low point. From the base station, parallel tunnels will be bored by TBMs to the location of large production caverns that need to be established for drilling and operation facilities. The concept has been found to be feasible and viable compared to traditional development concepts, and the associated cost and time schedules to be competitive for fields in the range of 30 km from the shore. Several challenges need to be tackled for a robust solution, but these are all considered being within the range of technology development. The concept reduces the environmental risk to a minimum, and improves the utilization of the oil field compared with traditional solutions.
The concept will however require further development of tunnelling methods and particularly TBM tunnelling with 300 m hydrostatic water head in difficult ground conditions, as the major challenge. This will require development by the TBM suppliers in terms of robust probing and pre-grouting facilities on the TBM for being able to investigate ahead of the tunnel face and to do a satisfactory pre-grouting to stop potential high pressure water inflow. Other issues that need to be further developed are the great demands on productivity and completion time of a field development project like this. Scheduling will require the TBMs to operate at high progress rates, around the clock and for several years, and with several machines at the same time. Thus, there is a requirement on robust and stable machines that need to be fulfilled. A project like this will offer suppliers possibilities for equipment development and breaking new frontiers on the technology level. This article presents the evaluations conducted to investigate the feasibility of such tunnels in the prevailing ground conditions in Northern Norway including time- and costs estimates.