The drilling or completing of exploration and development wells in today's offshore business will likely to continue to place an increasing demand on the present ageing Semi-Submersible fleet in the offshore presence. In respect of development drilling, operating and drilling companies require more complex wells to be brought on line in a timely and efficient manner such that the production cost per barrel is minimised. The need to enhance the capabilities of existing old Semi-Submersible units in order to meet these needs has never been greater. It is important that Operating Companies and Drilling Contractors align their respective goals both technically and commercially in order for both to remain competitive within their respective markets, and meet the needs of offshore activities,etc.
Some of the enhancements on the old rigs to cater for deeper water operation and more severe environment condition require the vessels to undergo some major conversions at shipyards before they are able to meet the new operational requirements, these include other considerations like :
* The change in the type of wells drilled in the offshore over the past few years, and also the type of wells that will be required in the future.
* The age and capabilities of the existing semi-submersible fleet.
* The change in market availability of semi-submersible units in the other sector.
* Rig characteristics required for the enhancement of current and future performance.
* The importance of Drilling Contractor and Operating Company goal alignment for performance improvements.
* The upgrading of second/third generation semi-submersible with (a) active heave compensation (b) 7500 psi circulating system (c) enhanced solids control capabilities, and the associated benefits plus rational behind these upgrades.
* Annual savings in the region can be achieved with the upgrades, depending on the daily operating costs and the total cost of upgrades including the life expectancy and extended useful life after the upgrade. Usually old rigs have gone through probably 30 years of service life and will only be extendable for another 25 years depending on the condition of the steel hull.
Over the past years, there has been a dramatic change in the type of operations performed by semi-submersible drilling units in the North Sea, gulf and other benign region, however, recent development started to look at far greater focus on directional subsea development projects along with deep water and HPHT wells, as opposed to the conventional exploration and appraisal wells. There is increasing trend towards bringing previous discoveries which were considered to be marginal from an economical prospective, on line by using new subsea technology coupled with reduced drilling costs through performance improvements. This change in activity coupled with a steady rise in the average age of the existing fleet of rigs forces us to ask the question, "How suitable are these existing units in terms of performance optimisation for the type of work that is currently being undertaken ?" Looking at the economics point of view, it may seem like conversion of old rigs may not be that economical than have new builts in the long term as well as the destination of the rigs to be operated. More importantly as an industry we must be asking ourselves the question, "How can we improve performance and within the operator's budget as well as meeting the performance required at site specific?" Alot of studies have to be initiated into reviewing the potential performance improvements that could be achieved through the upgrading of an existing semi-submersible unit and working out the sums right within budgetary plans. These potential performance improvements and economical impacts were also viewed in light of the rig type and the work programme that has to be executed.
Other major items on board the rig which impact the decision of conversion are :-
- Power generation of the rig
- The mode of mooring or using DP ( dynamic positioning ) to position the vessel on location
- The efficiency of drilling and handling of subsea operation
- The different types of rules and vessel notations to meet the site specific and classification impact
- The renewal of the existing systems to meet higher demand of the rig
- The number of crew onboard with upgrade as it would mean more men to handle a bigger and more complicated vessel to be operated
- The gain in variable deck load carrying capacity after extending and increasing the "bouyancy" of the vessel to allow it to carry more capacity and performance more offshore tasks
- Other aspects of the rig, such as rig motions with increased in pontoon sizes where waterplane area has related effect on motions, etc
Some of the features of upgrading are shown in below video :-
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