Research On Structure Response Of A Deep-water Semi-submersible Platform

The far-flung ocean has abundant resource and the exploitation area of ocean oil and gas is developing from offshore to deepwater and ultra-deepwater following the increase demand for oil and gas resource.As the depth of water increases,uniform platforms,such as jacket platform and gravity platform,are not suitable for deepwater exploitation of oil because of the great increase of self-gravity and cost.Therefore,deepwater platform becomes the focus for research.At present,the main platforms that can be used for deep-water oil and gas exploitation are TLP,Spar,and semi-submersible platform.Considering the investment cost,working water depth,the number of wells,service years,operating area and so on,the semi-submersible platform will be the best choice for oil and gas exploitation in the South China Sea.The sixth generation semi-submersible platform has appeared,and the research on it will not only shorten the distance of technology between us and aboard but also is the necessary demand of our economy development.The ocean environment of the world primary deepwater oil field is harsh.The semi-submersible platform can not avoid bad sea state which is different from other sailing ships.So the ultimate sea state in its life must be considered during the structure design.The platform should have enough strength to resist the harsh sea state that encountered in 100 years and ensure the security of the individuals and equipments on the platform.This thesis is the sub-project of the "863" program called "Key technology of semi-submersible drilling platform of 3000 meters water depth".According to the concept design of the sixth generation semi-submersible platform,the thesis analyzed the motion response in the design condition and especially the varied response following the wave frequency in the effect of wave force from all directions and then got the most disadvantageous combination of wave direction and frequency.Finally,it analyzed the whole structure's deformation and stress distribution in this loading condition.The paper describes the prediction of the semi-submersible platform wave loading and analysis method and procedure of structure strength evaluation.Firstly,it analyzes the necessary trend of the oil exploitation to the deep sea and introduces the present situation about deep sea oil and gas exploitation home and aboard.Then it simply introduces the major types and characters of deep sea oil exploitation platform and the development and structure style's change of deepwater semi-submersible in detail.The paper analyzes a deepwater semi-submersible using the actual values by the software SESAM developed by DNV.During the calculation of wave load,it uses the design wave method which based on 3D hydrodynamic theory.After obtaining the stress of the main structure,it checks the structure strength according to the stress standard regulated by the code,and it uses the finite element analysis method to evaluate the structure strength.The thesis finishes the topic well,and provides the basis for the research on deep water platform used during the deepwater oil exploitation in the South China Sea,and it has some reference value.