| Among the offshore oil and gas drilling equipments,as the foremost conduits,drilling risers connect floaters on the surface and the wellheads at the seabed and are critical to safe field operations.Riser deployment operation is an essential procedure during the offshore drilling operations,which is related to the normal development of subsequent drilling operations.To ensure the safety of drilling operations,the analysis of riser deployment operation has become a key research topic.This dissertation focuses on a deepwater drilling riser system in a semisubmersible drilling platform working in the South China Sea.The overall process of drilling riser continuous deployment from sea level to the wellhead is simulated with finite element analysis software ANSYS and AQWA.The influences of platform motion,platform drift velocity,riser lowing velocity,and sea state on the deployment of drilling risers are studied.The results show that slam force and wave force on BOP stack increase with the growth of wave height and decrease of wave period during the water entry of drilling riser.When the bottom of BOP stack arrive at sea surface and 17m water depth,slam force and wave force reach the maximum value respectively.Slam force on BOP stack increase with the growth of lowing velocity.The maximum slam force gets its the smallest value when deploy phase angle reaches π/2.Compared with deployment of riser in mooring status,drift running can decrease dramatically transverse deformation of riser.With the increase of the length of riser,the rotation angle of lower flexible joint decreases,and the effective tension and equivalent stress of riser increases gradually.The drift velocity has a significant effect on the top rotation angle of riser and rotation angle of lower flexible joint.The effective tension and equivalent stress of riser is affected markedly by the lowing velocity.During the drift running,the maximum equivalent stress is found below the top of the riser about 40m in the 1-year return sea state. |
