The paper describes the development of a novel solution for offshore loading of hydrocarbons, where the loading terminal is designed to keep the vessel being loaded/unloaded on station using dynamic positioning. The paper will describe the principles of the solution, and document the results from various work carried out such as model tests. The conclusion is that it will be possible to keep even the largest of vessels on station with a moderate power consumption compared to what is normally required for a DP system. The solution is expected to initiate a step-change in how tankers of opportunity are being loaded offshore, improving the availability, operability and safety compared to currently used solutions.
Offshore loading of tankers of convenience is done in two ways:
Ship-to-ship transfer (side by side or tandem)
Single Point Mooring
For large producing fields the ship-to-ship solution is deemed to be too risky by most oil companies, and is normally regarded as an emergency back-up solution only.
Traditional moored loading buoys are getting prohibitively costly as a function of large water depths. Further, coupled motions between a floating production unit and an offloading buoy can lead to excessive wear and fatigue issues, which is a well known challenge to the industry. By removing the moorings for the offloading system, and by making the offloading system water depth independent, an important area of concern can be eliminated.
Most of the oil tankers in the World are not equipped with any special means for offshore loading, other than mooring brackets on the bow and a handling crane midship. All regular tankers are therefore heavily dependant on use of assisting vessels such as tugs and linehandling boats for maneouvring, station keeping and hose handling. For large producing or remote field developments these vessels will become dedicated, and will become a significant addition to the operation cost.
The technology referred to as the HiLoad Technology has been developed over several years. The idea behind the technology was to use the experience gained from using purpose-built shuttle tankers in the North Sea, to develop a loading system that would incorporate these features even when used with a regular tanker. North Sea shuttle tankers are equipped with dynamic positioning, specialized equipment for mooring and hose connection and extensive safety systems. All onboard personnel go through training programs on a regular basis, such as emergency shut-down simulations.
An engineering and qualification program was undertaken in order to develop an offshore loading solution that would be able to maintain all the important features of a purpose-built tanker even when being used in conjunction with tankers of convenience.
The solution is believed to be of significant importance for how oil transfer will be done, especially as the search for oil is continuously getting into deeper waters.
The system is built up around a semi-floating steel structure, shaped like an "L".