الفهرس 
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Abstract
Offshore exploration and development have moved into deeper water and arduous environment, operators havestartedinvestigating ways to reduce well costs in order to make prospects anddevelopments, economically, more attractive. Among the keyavenuesconsidered to perform this is throughconducting drilling, testing andcompleting wells using jack-ups rig (JU) so as to replace the semisubmersible (SSDU) in intermediate water depth. A commonly held industry viewpoint is that deep water jack-up (Operation water depth 350-400 ft) is the preferred rig type over a shallow water semisubmersible (Operation water depth 300-1000 ft) from the perspective of daily rate, time of rig move and safety capabilities. In addition, a shallow water Semisubmersible total well cost isbasicallyhigher than a deep water jack-up. This thesis addresses the practical use of modem analysis techniques in the structural analysis which has been done by SAP2000, VIS and stability reassessment of offshore jack-up rigs in order to increase the working water depth (more than 400ft) by increasing the length of the three legs. Furthermore, thethesis intends to examine the ability to extend the jack-up leg to work in deeper water without any problems related to the structure or stability aspects. Checks have been conducted for 50 year return period storm conditions in five different water depth scenarios. Additionally, the objective here is to ensure safe, reliable and economic operation during the drilling and rig move operations.
The GSF CONSTELLA nON II, jack-up rig was selected in this thesis as a case study. The member failure probability of the leg components after extension up to 659 ft at storm boundary condition in higher water depth is considered the most important factor proven by the results which have revealed significant damage in leg members. Thus, it was concluded that this type of structural failure deserves greater attention during the extensi?n stage of jack-up legs. In addition, the draft exceeded the load line marginand the allowabi’e VCG was not acceptable. The outcome, of,this study is the development of a method to examine the possibility of extending the legs of jack-up rigs based on the API acceptance criteria and stability requirements.