Jack-up Reinstallation Near Existing Footprint
Jack-up platforms are being used extensively in the offshore oil and gas industry and can operate in water depths up to around 120m. The foundations of the jack-up platforms are known as 'spudcans', which have a typical diameter of 20m or more.
Large footprints often remain on the sea-bed after spudcans have been removed. In soft clays, the footprints can be more than 20m deep and wide, with large variations in soil strengths below the surface. Jack-up reinstallation close to these footprints is often necessary to drill additional wells.
This could, however, induce large lateral forces and bending moment loads on the spudcans and subsequently on the jack-up legs. When the loading exceeds the design capacities of jack-up legs, severe damage might result, leading to catastrophic failure.
The objectives of this study are to:
1) Investigate the mechanisms involved in the development of bending moments and lateral forces in jack-up legs during reinstallation nearby an existing footprint, accounting for the geometry and strength characteristics of the footprint and the structural characteristics of the jack-up unit.
2) Formulate a framework to predict the spudcan reinstallation response;
3) Quantify the risk associated with the spudcan reinstallation;
4) Formulate effective mitigation measures when appropriate and quantify the reduction of risk associated with these measures.
The novelty of the research lies in the coupling between the geotechnical aspects of the spudcan reinstallation and the structural aspects of the jack-up unit.
The jack-up reinstallation problem has caused a number of failures in the past. According to Dier et al. (2004), this problem continues to be the second-highest rate of cause in jack-up installation incident.
The completion of this project is expected to lead to a better understanding of the problem. From this understanding, recommendations of safer practices and mitigation measures could be developed to avoid the potential failure of reinstalling jack-up near existing footprints.