Research On Mechanical Characteristics And Construction Parameters Optimization Of Marine Deepwater Drilling Riser System

More than 90% undiscovered offshore oil and gas were buried at a depth of more than 1000m water. Therefore, deepwater drilling is the key to push oil industry forward the development, but the depth has seriously hampered the development of deepwater drilling. The riser is the critical equipment to make the connection between drilling rig and SBOP, which is easy to suffer the failure due to wearing and crack under the coupling effect of marine environment and drilling condition. There are numbers of severe economic losses and security issues.Consider of the complication of load to buoyancy can riser system, this paper carries out calculation of the load. It contains ocean current, vortex and wave load. Among them, for ocean current load, the method of calculating velocity profile of deep ocean and shallow ocean has been put forward, and analyzes the value difference between this two wave profiles by comparison to clear the limitation of shallow ocean velocity profile and the necessity of establishing the deep ocean velocity profile. Ultimately, the load of system is showed with micro bit form in the ocean wave load calculation model in this paper. For vortex load, this paper finds out the calculation formula combine with the Characteristics of the vortex and Stowe Hal. Study finds in this paper that the calculation value of wave load and vortex load presents little deviation if the shallow ocean model is applied and that will have a negative effect on the accuracy of riser design and growing the operation risk.This paper established the wave load calculation model. first, this paper find out resistance coefficient and inertia coefficient, then calculate the value combining with Morison formula. The study found the waves and eddy current load variation in line with changes of the sine and cosine functions, this law is conducive to the process of calculation and analysis of applied mechanics. It is found that wave load and vortex load which is the critical factors in the project of buoyancy modules allocation, plays the decisive role in the energy of rises.This paper established a Fourth Order mechanical response equation of riser, used the finite difference method to solve the equation, the method has good convergence, fast convergence, small iterative error. Program analysis software of riser buoyancy system which can be applied to design analysis the normal conditions, extreme working conditions, working conditions and emergency off suspended condition, can optimization buoyancy block configuration, top tension and drilling fluid density configuration parameters and other conditions. It was found that top tension can influence the stability of riser system greatly, if the tension is unable to provide enough top tension for riser, buoyancy modules should be installed. Thereby reducing the amount of lateral offset riser, moment and stress, maintaining stability of riser system and ensuring the normal drilling process.Systematical analysis software of riser programmed in this paper can contribute to the design and test the safety of rises.