New technologies and solutions are increasingly more critical in the oil industry to develop marginal fields and maintain the oil production rates of more mature fields. In recent years several successful raw seawater injection systems have been implemented and new subsea water treatment technologies are under development, enhancing the methodologies and techniques used.
This paper describes the potential use of floating wind turbines for powering subsea water injection facilities, stand-alone systems', and discusses these systems' technical and economic feasibility compared to current solutions. High-level indicators of economic and technical performance show an interesting window of opportunity for applications that can tolerate unprocessed seawater for injection in oil fields. Other configurations can also be attractive.
The simplest use case considered for this article is powering a subsea pump with a local, offshore floating wind turbine to inject unprocessed seawater into an oil reservoir. Other related cases for floating wind turbine powered injection pumping are identified and discussed. Recent experience on a subsea water injection project on the Norwegian shelf has demonstrated the technical viability of injecting unprocessed seawater into an oil reservoir with suitable properties. Further, successful floating wind turbine demonstration projects have proven this new technology's feasibility.
In the conventional solution for a subsea injection manifold, the costs associated with connecting a subsea power cable to the host platform, where the electrical power for the subsea injection pump is generated, can be substantial. Under the right circumstances and conditions, it may be possible to reduce costs significantly by powering the subsea pump with 1-2 offshore wind turbines that are placed in close vicinity (in the order of hundreds of meters) of the subsea manifold. The reduced costs of this solution are enabled by the shorter subsea power cable, the elimination of incremental power generation on the host platform and, in the case of Norway, reduced taxes related to the incremental emissions of natural-gas turbine power generation for the subsea injection pump.
A study has been performed where the main technical challenges of the wind-powered subsea injection pump have been considered and are judged to be fully manageable. The most significant of these are related to the intermittency of the wind turbine power generation. Wind turbine output characteristics can be designed to produce power even at low but non-zero wind speeds. The optimization problem statement for choosing a wind turbine for this application is therefore very different to the more common challenge of maximizing energy output from wind turbines installed at a particular onshore site.