A reliability study of a Deepwater Vertical Xmas Tree with attention to XT retrieval rate
A reliability study of a Deepwater Vertical Xmas Tree with attention to XT retrieval rate
复制标题
DOI：
--
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Oda Ingeborg Stendebakken
中科院分区：
文献类型：
--
作者：
Oda Ingeborg Stendebakken
本文的重点是海底圣诞树（XT）系统。XT被业界公认为整体可靠的配置，但与所有开发项目一样，考虑到安全性、可用性、可维护性和可靠性等几个方面，从生命周期的角度优化设计是一场持久战。设备的计划外停机导致设备停机时间长，维修成本高，维修时间长，以及与生产损失相关的高额罚款。主要目的是研究特定的XT系统，并根据商业上可获得的可靠性数据估计由于采油树故障导致的采收率。此外，这应与所提供的高水平经验数据进行比较。这是为了启动这个过程，以减轻与已知现场经验相比，树检索率的一般计算之间的差距。所选择的XT配置是深水垂直圣诞树（DVXT）。在GE Oil & Gas主管Endre Willmann的帮助下，构建了一个广义案例作为DVXT。在这种情况下，范围仅限于DVXT系统和影响DVXT系统的采油树检索率和由于采油树系统故障而导致的停机时间。因此，水下控制系统及其相关监控设备不包括在分析范围内。为了评估DVXT系统，进行了可靠性分析。可靠性分析采用可靠性工程学科中已验证的方法，分以下步骤完成：FMECA/失效分析RBD/可靠性分析进行组件级FMECA，以了解具有基本功能要求的主要组件以及功能失效的临界性和影响。采用自底向上方法进行的可靠性分析结果表明，采油树的恢复率接近22年。通过可靠性分析，证明了DVXT系统是一种运行可靠性高、风险低的可靠配置。尽管如此，还是做出了一些假设。本文的重点不在于提示的绝对结果，而是说明GE Oil & Gas在基于通用可靠性数据与经验数据进行可靠性计算时遇到的一个可靠性问题。它显示了自下而上的方法和所提供的经验数据之间的显著差距。根据收集的野外经验，指出自上而下的方法在100 ~ 200年之间是XT检索的最佳时间跨度。这意味着自底向上方法和自顶向下方法之间有5到10倍的差别。此外，GE Oil & Gas指出，在决定故障是否需要进行重修井（如XT回收）或轻干预（如ROV修复）时，似乎适用帕累托规则。将灵敏度情况应用于自下而上方法，假设实际上80%的临界故障可以通过轻度干预手段恢复，则预测的临界故障总MTBF为15年，则XT恢复率为75年。这较接近由上而下的方法所显示的期望，但仍不接近最近外地经验所显示的水平。这表明自下而上的模型应该使用基于经验数据的输入数据进行校准，而不仅仅是通用的，以减轻两种方法之间的一些距离。这可以以附加模型参数、修改因子或其他改进的形式进行。对于这些模型参数，本文的结果并没有给出明确的答案，因为没有找到相关的文献。如果基于全面的历史数据显示适用，可以利用帕累托规则来校准这一差距。这件事必须进一步深入研究。
The focus of this thesis is towards the subsea Xmas Tree (XT) system. The XT is recognized by the industry as an overall reliable configuration, but as in all development projects, it is a constant battle to optimize the design in a life cycle perspective taking account of several aspects such as safety, availability, maintainability and reliability. Unplanned stoppage of equipment result in high equipment downtime, high cost of repair, extensive repair time and high penalty associated with loss of production. The main objective is to study a specific XT system and to estimate the retrieval rate due to tree failures based on commercially available reliability data. Further this shall be compared to high level experience data presented. This is to initiate the process to alleviate the gap seen between generic calculations of the tree retrieval rate compared to known field experience. The XT configuration chosen to evaluate, is the Deepwater Vertical Xmas Tree (DVXT). A generalized case was constructed as the DVXT with help from Endre Willmann, the supervisor in GE Oil & Gas. The scope is limited in this context to the DVXT system and systems that influence the DVXT system in terms of tree retrieval rate and downtime due to failures in the tree system. Therefor, the subsea control systems with associated monitoring equipment are excluded from the analysis. To assess the DVXT system, a reliability analysis is performed. The reliability analysis is achieved in the following steps with proven methods from the reliability engineering discipline: 1. FMECA/Failure analysis 2. RBD/Reliability analysis A component-level FMECA is conducted to develop an understanding of main components with essential functional requirements and criticality and effect resulting from functional failure. The results from the reliability analysis conducted as a bottom-up approach indicate a retrieval rate of the production tree near 22 years. The DVXT system is shown to be a reliable configuration with high operating reliability and associated low risk through the reliability analysis. Nonetheless, several assumptions have been made. The focus of this thesis is not at the prompted absolute result, but to illustrate a reliability issue experienced by GE Oil & Gas when calculating reliability based on generic reliability data contra experience data. It is shown a significant gap between the bottom-up approach and the experience data presented. Based on the field experience collected it is indicated a MTTF for XT retrieval on the top-down approach between 100 to 200 years. This implies a factor of 5 to 10 between the bottom-up and the top-down approach. Further, it is indicated by GE Oil & Gas that a Pareto-rule seem to apply when deciding if failures require heavy workover such as XT retrieval or light intervention means such as ROV remedial actions upon repair. Applied to the sensitivity case to the bottom-up approach, assuming that in fact 80% of XT critical failures can be restored by light intervention means, the total MTBF of 15 years predicted for XT critical failures then results in an XT retrieval rate of 75 years. This is closer to the expectations indicated by the top-down approach, but still not close to the levels indicated by recent field experience. This indicate that the bottom-up model should be calibrated with input data that is based on experience data rather than only generic to alleviate some of the distance between the two approaches. This can be performed in shape of additional model parameters, modification factors or other refinements. The results from this thesis give no clear answers to such model parameters, as no literature were found on this issue. The Pareto-rule can be utilized in order to calibrate this gap, if shown applicable based on comprehensive historic data. , This has to be studied further thoroughly.