Perforation Drilling and an Innovative Spudcan for Mitigating Punch- Through in Multilayered Soils

Abstract

Abstract Spudcan foundations for mobile drilling rigs continue to exhibit a high failure rate in the offshore oil and gas industry. The more frequent use of larger jack-ups in highly stratified regions, such as the Sunda Shelf in Southeast Asia, contributes to this concerning increase in ‘punch-through’ incidents, which can lead to buckling of the leg or even toppling of the rig. This paper reports measures for mitigating spudcan punch-through in multilayered soils. Centrifuge model tests were carried out on spudcan foundations penetrating through multilayered soils with interbedded stronger layers.The model tests included half- spudcan tests against a transparent window, allowing visualization of the soil flow, and full-spudcan tests to measure penetration resistance. The soil conditions tested simulatedoffshore strength profilesthat have reported punch-through failures, such as on the Sunda Shelf in Southeast Asia, Gulf of Thailand, South China Sea, offshore Australia and the Arabian Gulf. An experimental method for ‘drilling’ sites in the enhanced gravity environment was developed. An innovative spudcan was developed to integrate directly to a jack-up rig to be used where there is a potential for punch-through hazard. The experimental results show that for layered clay deposits, potential of severe punch-through failure can be eliminated by means of perforation drilling or using an innovative spudcan. For sand-over-clay sediments, using skirted foundations or the innovative spudcan allowed for eliminating the likelihood of failure. The results also show that spudcan-footprint interaction issues for reinstallation of a rig can also be mitigated through perforation around the spudcan periphery.