First Hyperstatic Riser Joint Field Tested for Deep Offshore Drilling

摘要

The long riser is the key element for deep offshore drilling.The total weight of the system increases rapidly with the waterdepth in the same way as the required tensioning capacity.Static loads and fatigue become critical and threaten the riserintegrity. Furthermore, the natural period of the riser in thedisconnected mode reaches the wave energy window andseems able to put the riser in a dangerous resonant state.A new technology developed by IFP for integrating riser jointsis presented in the paper which allows to reduce by up to 30%the weight of the system and to significantly lower the naturalperiod. It consists in joining together all the pipes constitutingthe riser (main pipe and peripheral lines) in so manner to sharethe axial tension between all of them. This hyperstatic workingmode may be used conjointly with hybrid (steel/composite)kill & choke lines previously developed.After a first step of riser analysis and technical studies throughextensive FEA and CAD, a field test was decided to bringinformation on the capacity of the technology to workproperly in the operational context of a drilling rig and tomaintain in the time the hyperstatic working mode of the riserjoint. The Pride Angola drillship was chosen for the test. Apreliminary phase consisted in designing all the mechanicalchanges to achieve in the riser joint: adding two hybridauxiliary lines, fixing the lines at both ends, integrating partialinstrumentation (6 sensors). Then, a qualification phaseconsisted in carrying out all laboratory tests of the relevantequipment. A special testing fixture was built at IFP for thatpurpose. The operating phase started July 2005 for a minimumof 6 months and data was recorded during drilling operationsto check the working conditions of the riser joint.The paper presents the basis of the technology, describes thethree phases of the field test and comments the first resultsobtained from the rig. To conclude, the technology is then putin the context of deep sea drilling and its benefits arediscussed for conventional, slender and dual gradient risers.