New standard for jack-up site assessments

justsun

Tuesday, 21 December 2010 06:06  
More than 30 oil and gas experts from around the world meeting at GL Noble Denton in Hamburg recently have tried to insert a jack-up section into a new international standard for site-specific assessment of mobile offshore units.


Before the end of the year, the work group, made up of class societies, designers, shipyards, oil companies, drilling contractors and authorities, intends to submit their results as the final draft of a new standard for site assessment of jack-up platforms to the International Organisation of Standardisation (ISO).
The work group is chaired by Mike Hoyle, Chairman of the GL Noble Denton Technical Policy Board.
All mobile offshore units, and particularly self-elevating (drilling) units (jack-ups), are subject to an unusual design and assessment process. These structures need to be not only designed to a set of criteria such as owner's specifications, classification society rules, and flag state requirements but also need to be assessed for each new location at which they are to operate.
Jack-up platforms are used for offshore oil and gas exploration, work-over and maintenance and wind turbine installation. They move from one location to another on their buoyant hulls. In operation their legs are founded on the sea floor and support the hull above the waves. The larger units can operate in waters in excess of 100 metres.
Site assessments are necessary because jack-ups move from location to location on a regular basis, each location offering a new set of unique conditions. Not only will the water depth be different, but there will be differences in the foundations, the environmental conditions, rig orientation, air gap requirements for work over and required variable load.
In addition, there could be a different set of requirements for each location as a result of local regulations and specific user requirements. The two most critical areas are the predicted meteocean extremes at the site, and the foundation.
The site specific assessment of jack-ups has evolved over the years from a relatively simple, pragmatic assessment based on a series of trade-offs to a much more rigorous detailed assessment that may involve nonlinear time domain dynamic analyses incorporating detailed soils models. The standards used to address the feasibility of jack-up operations have also had to follow this progression, carefully controlling what is determined to be acceptable, but without stifling technological advances.