Study of Offshore Wind as Power Supply to Oil and Gas Platforms

Abstract

Abstract Offshore petroleum installations are conventionally equipped with local powersupply based on fossil fuel, e.g. gas turbines. Alternative power supply suchas wind power has a large potential to reduce the fossil fuel use, and therebythe CO2 and NOX emissions. Potential benefits with such a solution areinvestigated in this paper by considering a system consisting of fiveinterconnected oil platforms connected to a 100 MW offshore wind farm. Theplatforms are assumed to have a constant load, 147 MW in total. Two parallelgas turbines are still present on each of the five platforms, but the windpower always has first priority to supply the load. A one-year simulation hasbeen made using wind power data. Compared to the case without wind power, anoverall reduction in fuel consumption of 21–32 % was found, depending on theoperation strategy for the gas turbines. The gas savings yield revenues thatwere used to calculate the break-even cost for the wind farm investment. Arough estimation indicates that a wind farm investment cost smaller than 2.0M€/MW would make the combined wind/platform solution favourable compared withthe default configuration. As this calculation is highly dependent on a numberof parameters, a sensitivity analysis is conducted that quantifies thedependency between different parameters and the break-even wind farmcost. 1 Introduction Offshore petroleum installations are largely isolated systems with a localpower supply consisting of local gas turbines (or other turbines based onfossil fuel). These turbines have low efficiency ratios (about 30 % on averagecompared to about 55% for a modern combined cycle gas power plant), and emitconsiderable amounts of CO2 and NOX [1]. Due to climate change concerns, thereis a world-wide focus on reducing CO2 emissions, and a tax on CO2 emissions hasbeen introduced in many countries as a means to reach this goal. The potentialfor reductions in fuel consumption and CO2 and NOX emissions throughelectrification of offshore platforms is large. There are two main alternativesfor electrification. One is to connect the platforms to the onshore powersystem via cables. The other alternative, and the topic of this study, is toconnect the platforms to alternative offshore power production in isolatedpower systems. A combination of these two main solutions is also possible. Themost realistic candidate for renewable offshore power generation today isoffshore wind. This paper describes results from a (hypothetical) case study of multipleplatforms connected to an offshore wind farm. The focus of the study is tocalculate potential reductions in fuel use and emissions through introductionof wind power as supply to a system of multiple oil platforms. In addition, economic calculations with respect to the fuel savings and wind turbineinvestment costs are included to indicate the potential profitability inconnecting wind power to oil platforms. Finally, energy storage systems arediscussed as a further modification to the conventional offshore power systems. Storage can yield a more efficient fuel gas usage while at the same timeprovide a higher security of supply. A study with a similar focus has been carried out previously on a simplersystem with only one oil platform [2]. The same system as studied in this paperhas been investigated in two previous studies, focusing on control and powersystem stability issues [3] and on fuel saving [4], respectively. Otherstability studies on small isolated systems with wind turbines and oilplatforms are found in [5–8], and diesel-wind systems was investigated in [9,10]. An on-going real life demonstrator project where two 5 MW wind turbinesare connected to the Beatrice oil platform is described in [11].