Exploration • Drilling • Field Services
Conquering the challenges of harsh environment jack-up design
Harsh environment jack-up rig design must balance multiple criteria, from climate to reservoir characteristics. Careful attention to these factors can maximise the productivity – and marketability – of the rig. John Knowlton reports.
I
t has been a truism in the energy industry for the last decade that the easy oil is gone. Recent discoveries have expanded our view of the world’s potential recoverable reserves, but tapping those resources demands increasingly complex technology. For offshore oil and gas, advances in rig design
are an essential piece of the solution. While much of the attention has focused on deepwater vessels, shelf exploration is also facing technological challenges that require new approaches to jack-up rig design. In developing the specifications for its most recent series of newbuild harsh environment jack-ups, Ensco looked for solutions to two major hurdles in order to expand the ‘area of operability’ of the vessels: environmental resistance and drilling capability. Te goal was to expand the potential market footprint while maintaining a cost-effective design approach. In the North Sea, area of operability (based primarily on water depth and environment) is
a frequent measure of functionality, as shown in Fig. 1. In the intense wind and wave action that typifies the North Sea climate most of the year, operating in 400-foot water depths is a significant step forward from operating in 350-foot water depths – the current limit for most harsh- environment jack-ups. Ensco, however, broadened the area of operability concept to a global scale, to look for the ‘sweet spot’ in design specifications that would create the maximum geographic range for the rigs with the greatest economic value for both Ensco and clients. As a starting point, Ensco used the Keppel
FELS Super A Class rig, designed for the harsh environment of the UK sector of the North Sea.
Environmental capability Harsh-environment jack-up designs must adequately address the issues of low service temperatures and the forces of wind, waves and current.
Fig. 1. North Sea Operability Map.
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