Structure Study On Single Pile Based Simplified Offshore Platform

Using offshore simplified platform structure is one of the effective means to develop marginal oilfield. The simplified platform structures whose structure stiffness and redundancy are smaller than regular platforms are mainly used for unmanned platforms.Single pile based simplified platform structure is a kind of simplified platform which is suitable for marginal oilfield exploitation in shallow sea. Its upper deck structure is supported by one steel pile in which the condutores are installed. As a new type of structure, its application in ocean engineering has created a precedent in our country. The deck load is undertaken by the single pile which has small lateral stiffness, thus the upper deck will have large horizontal displacement under the environmental load.Based on the structure features of the single pile foundation, some relevant researches have been done. The following paragraph lists the subjects we do and our achievements.(1) According to environmental conditions in the oilfield, the platform function, the relevant rules and papers, we have made a detailed and precise structure design for the single pile based platform. With the proper pile diameter, pipe thickness, driving depth and deck clearance defined, a kind of single pile based platform structure which have good mechanical properties has been obtained.(2) According to the design environmental conditions, we combine the loads acting on the platform to get some worst combinations and the static analysis has been done. The basic loads include wave load, current load, wind load, ice load, deadweight, buoyancy, equipment load, live load and so on. The combined loads include loads in operation condition and loads in extreme condition.(3) The response of the platform under wave force is studied. The analysis we do consists of fatigue analysis, dynamic response analysis under extreme wave load and collapse analysis. The analysis results show that the platform structure can fulfill the service life and strength requirements, besides of that, the structure has good strength reserve and can resist the loads in abominable environment.(4) Seismic analysis which is composed of structure strength analysis and toughness analysis has been done for the platform too. The results show that, the platform structure can reach the seismic requirements and resists the seismic loads even during strong earthquake.(5) As a finite element software, ABAQUS is used to do the interaction analysis of pile and soil for the single pile based simplified platform under lateral loads. The material nonlinearity of soil, the nonlinearity of contact boundary between soil and pile, the geometric nonlinearity of the soil large deformation are all taken into consideration. Through the analysis, we get the pile displacement and the pile stress,the values are small enough to rearch the design requirement.By the research demonstration for the single pile based simplified platform structure, it is concluded that this structure is feasible for the offshore oil platform.