The Research On Drilling Riser System Of Offshore Deep Water

All over the world, nearly 90% of undiscovered offshore oil and gas reverses lie in deep formations above which seawater is more than 1000m deep. Offshore oil and gas wells are critical to the future of oil and gas industry. Deepwater is one of the most important factors that restrict offshore deepwater drilling very badly. As to offshore deepwater drilling, marine riser has being become a major problem because of the troublesome working environment caused by deepwater. In order to design and use riser freely, it is necessary and important to study riser's working state and complex loadings on it with static and dynamic mechanics.Having analyzed the latest development of offshore deepwater drilling, especially the latest advances of riser technique, the paper studies the working state of riser systematically by non-linear finite element method, and develops a new way to study and design riser for future offshore deepwater drilling.With fluid mechanics methods, wave theory methods, and other theoretical methods, the paper studies the environmental loadings on riser, such as ocean current loading, wave loading, and other loadings; develops a strong support for calculating environmental loadings, and for studying riser's distortion and strength.The paper develops a three-dimensional non-linear finite element mechanical model for offshore deepwater drilling riser; analyzes riser with 3-D static and 3-D dynamic mechanics; studies the distortion of riser, bending loading on riser, types and frequency of riser vibration, dynamic displacement and dynamic stress of riser. In above studies, the micro strain and macro distortion of riser, and the axial loading on riser have been taken into account and embodied in non-linear theory. Consequently, the analyzing results accord with truth much better. The calculating results of the mechanical model tally very well with the corresponding data in the relevant reports provided by SPE API.The paper analyzes the important elements which restrict the operation of offshore deepwater drilling riser, including tensile force in top riser, the angle ofbottom globe joint, floats, depth of sea water, and the effects of environmental loadings on riser distortion and strength. The studying results are helpful for designing and using offshore deepwater drilling riser correctly and effectively.