Abstract
Perforation drilling is a promising technique to mitigate the sliding risk of jack-up units installed around footprints. Based on the coupled Eulerian–Lagrangian (CEL) method, a 1/2 finite element model, including a rigid Lagrangian spudcan and a Eulerian soil part, was established, and the contact interface was modelled with the Coulomb friction model. Validated against an indoor perforation test, the model was adopted to investigate the mitigation mechanism and effects of the borehole diameter, number, depth, and the drilling range. The simulations reveal that the mitigation efficiency increases with the borehole diameter, number, and depth. However, it shows little improvement if the borehole depth increases beyond double footprint depth. The semi-drilling at the outer side of the footprint is a little more effective than the full-drilling at both the inner and outer sides of the footprint. The present work emphasizes the effects of perforation drilling parameters on the mitigation efficiency, which are of great significance to guide the engineering practice and guarantee the safe operation of the jack-up reinstallation close to existing footprints.
Highlights
The jack-up unit is widely used in offshore drilling and exploration due to its significant mobility and economic efficiency
When the jack-up unit has to be installed in the vicinity of a footprint, the spudcan may slide towards the footprint, as adverse horizontal forces and bending moments on the spudcan would be induced due to the asymmetric ground underneath
Study of the sliding risk during spudcan re-installation close to footprints and its mitigation measures are of great significance to the operational safety of jack-up units
Summary
The jack-up unit is widely used in offshore drilling and exploration due to its significant mobility and economic efficiency. Study of the sliding risk during spudcan re-installation close to footprints and its mitigation measures are of great significance to the operational safety of jack-up units. It is only in the last two decades that much attention has been paid to the re-installation of jack-up units near existing footprints. Mitigation measures to alleviate the sliding risk during the spudcan installation close to footprints can be divided into two categories, namely, footing modifications and seabed modifications [15]. Hossain et al [20] and Hossain and Stainforth [21] conducted preliminary tests on the “perforation drilling” through experiments and verified the effectiveness of the method in mitigating the sliding risk. They are believed to be of great significance for future engineering practices
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