New jack-up concept for Arctic conditions

Abstract

Arctic exploration is one of the main trends in today’s oil and gas industry. In shallow waters jack-up mobile drilling units are often used for drilling outside the ice season. The operating period of the jack-ups is strictly limited by the ice conditions. The jack-up should be transported to the site after the ice cover has cleared sufficiently and should be moved away before the sea freezes up. A new concept of jack-up suggested by Ove T. Gudmestad (University of Stavanger) is considered in this thesis. The concept comprises a hull with icebreaking capabilities and four columnar legs placed on outrigger arms and equipped with protective collars so the jack-up can withstand ice loads in the early ice period. Drilling through one of the jack-up legs is suggested to protect the drill string from the ice impact. The leg should have a telescopic design so that the derrick could be skidded over it before drilling. The purpose of the thesis is to evaluate the feasibility of a concept suggested for extended drilling season in Arctic waters. The important design issues i.e. protective collar geometry, required air gap, telescopic leg design, collar fixation system etc. are discussed. Wave and ice loads on the jack-up legs are calculated and the possible extension of the drilling season is estimated. The benefits of the new concept and its potential applications are discussed.