【作者】 冯义然；

【导师】 王银邦；

【作者基本信息】 中国海洋大学 ， 防灾减灾工程及防护工程， 2011， 硕士

【摘要】 近年来频发的能源危机使人们把越来越多的关注投向海洋资源,尤其是海洋油气资源。而目前,我国的大型油田均已过产量峰值,这就要求要有新的油田来缓解这一矛盾。位于渤海湾的胜利油田尚有大量的浅海油田可供开发,然而这些油田很大一部分属于“边际油田”,而且位于沿海滩涂区域。这就要求开发者不仅要设计出满足软土地基的采油平台型式,而且该平台要满足“边际油田”开发所需要的经济性。因此,传统的导管架平台很难满足这些小型油田的要求了,必须设计新型的低成本、可重复利用的平台型式。本课题所采用的是使用桶形基础作为入泥裙板的新型重力式平台作为采油平台,针对油田产量进行平台的尺寸设计并对其构件比例进行了合理性判定。由于投产之后,平台首先要承受日常工作载荷——作用于沉箱底部的随时间均匀变化的循环储油载荷,故而首先进行桶土稳定性的判定。此外,渤海湾位于地震活跃带上,平台要承受随机地震的影响;平台安装位置的高纬度平台会受到大质量冰块或者浮冰群的撞击作用,渤海湾波浪较高,这些都可能引发平台与环境载荷的“共振作用”。因此,鉴于海洋平台在经济上和社会上的重要性,必须对其静动力稳定性进行判定。本文主要做了以下几方面的工作:(1)分别针对桶形基础和重力式平台的研究背景和国内外研究现状进行了总结和概括,提出了亟待解决的问题。(2)对适用于渤海湾“边际油田”的新型平台—应用桶形基础的重力式平台进行了尺寸设计和材料选择,保证控制成本,实现“边际油田”开发的经济性。(3)针对所设计的平台,制作了比尺为1/25的模型并使用该模型进行缩尺试验。首先,配置以黄河三角洲原状海底土作为平台的安装基础。其次,根据渗流原理布设总应力传感器和孔隙水压力传感器以分别监测模型试验中的土中应力,并通过编程实现了模型数据与原型试验数据之间的转换。再次,分别应用系列Drucker- Prager失效准则和Mohr- Coulomb强度准则,并辅以数值模拟试验(考虑“边界条件”和不考虑“边界条件”)以判定在日常循环储油载荷作用下地基土的应力状态和失效性判定。最后,根据以上结论确定出沉箱经济合理的储油量为1000吨。(4)此外,应用有限元方法对所设计的平台在可能遭受的海洋环境载荷作用下的结构稳定性进行了分析。首先,使用两组调幅的强震记录和一组人工地震波进行了平台的地震时程分析。从中可以看出,与水平方向相比,竖直方向上的响应量很小。通过绘制平台沿竖向各节点的位移时程曲线和最大位移包络图可以得出如下规律:平台在强震作用下的变形以第一、二阶振型为主,而且在12m高度以下,立柱节点高度越高,位移响应值越小,12m左右时达到最小,之后随高度增大,位移响应值增大,但是结构始终没有失稳。其次,使用大质量冰块简化模型和浮冰群的冰激振动模型对平台冬季可能承受的海面冰载荷进行了模拟,认为平台在浮冰群连续撞击造成的周期性激振载荷作用下的动力系数较大,其响应要远大于简化模型。最后,对平台在波浪载荷作用下的动力响应进行了模拟,认为平台在指定波浪谱的作用下可能发生“共振”,这在工程中要加以避免。更多还原

【Abstract】 In recent years,“Energy Crisis”happened more and more frequently, which made people pay increasing attention to offshore natural resources, especially oil and natural gas. However, daily production of most fertile oil fields passed their peak yields, which makes it urgent to explore new reservation so as to settle the problem. It is reported that Shengli oil field which is located in Bohai Bay, has large area of virgin fields for exploitation. However, a large portion of them are“marginal fields”and located in muddy soft foundation. This demands the developer design offshore platform that could not only be applicable for the soft foundation, but also satisfy the economy of the whole project. Therefore, traditional jacket platform which consumes more piles and steel bar cannot meet the requirement of these small oil fields. Instead, new movable platform with lower cost should be designed and adopted.In this paper, a new concept of gravity platform with skirt plate is introduced as single bucket foundation, the dimensions are designed and its rationality is also analyzed according to daily yields of the oil field. When put into practice, the platform will firstly be exposed to working loads- daily oil loading exerted on the caisson bottom in vertical direction which changes evenly with time. Moreover, the Bohai bay is located on active seismic belt area where random seismic loading may affect the safety of the platform. In addition, relatively high latitude would cause the water freeze and expose the platform to ice blocks and/or ice clusters; The harsh sea wave occur everywhere in Bohai Bay, all of which would lead "structural resonance". In consideration of the economic importance, environmental significance and all possible factors mentioned above, tests should be performed to determine the static and dynamic stability, both in geotechnical meaning and structural meaning.The content of this text includes the following four parts:(1) The background and research progress about bucket foundation and gravity platform respectively are introduced separately, the current proceedings both home and abroad are summarized and the problems to solve are put forward.(2) Based on the practical soil conditions and productivity of oil fields in Bohai Bay, a new concept of platform- gravity platform with single bucket foundation is introduced and designed, then the dimensions and fabricating materials are initially quantified so as to control the cost and expand the profits.(3) A scale ratio of 1/25 is chosen for laboratory reduced-model tests. First, characteristics of soil samples selected from Bohai Bay are quantified and the foundation soil in reduce-scaled model test is formed with the original soil. Second, according to the seepage principle, total stress transducers and pore pressure transducers are pre-buried in the soil so as to monitor the stress state, and then the model test data is converted back to the prototype state through MATLAB programming. Thrid, referring to numerical simulation, a series of Drucker-Prager yield criteria and Mohr-Column strength criterion are employed respectively, so as to judge the credibility of the model data and determine the yield strength. Fourth, based on the conclusions reached above, the oil capacity of the caisson is quantified as 1000 tons.(4) The structural stability of the platform under possible environmental loadings is analyzed through finite element method. First, response of the platform under random seismic loading is simulated with 2 groups of amplitude-modulated actual seismic record and 1 group of artificial earthquake wave. It is seen from the analysis that in contrast with the horizontal response, the vertical response is slight. It can also be concluded from the time-history displacement and maximum nodes displacement that under random earthquakes, the deformation of the platform is mainly in accord with first and second vibration modes; In the vertical direction, absolute displacement response of the column nodes decreases with the height when the height is smaller than 12m; when greater than 12m, it increases with the height. Second, the ice loading in the winter is simulated with simplified concentrating mass model and/or ice induced vibration model of ice cluster. Through finite element analysis, we can see that dynamical amplification effect is obvious under cyclic loads induced by ice cluster and the displacement response is much bigger than the concentrated mass model, thus the ice induced vibration should be adopted for analysis. Third, the possible response of the platform under specified wave spectrum is also analyzed, which is concluded that“structural resonance”may happen under specified sea wave spectrum, this should be avoided in engineering practice.更多还原