Blowout Preventers (BOP) are safety devices used to prevent uncontrolled flow of liquids and gases during a blowout. Blind Shear Rams (BSR) is one of the critical components of a BOP responsible for shearing the drill pipe and sealing the wellbore during a blowout scenario. Tests were conducted by shearing a drill pipe under non-flowing conditions to obtain the maximum shearing force, shape of sheared drill pipes, shearing time. A FE methodology has been developed to model the shearing process using Abaqus Explicit finite element solver. Simulations were performed to replicate the shop test and the results are compared with the shop test and found to be in good agreement. The current study uses a validated model for evaluating some of the challenges being faced by the BOP shear ram technology. These include drill pipe centralization in the well bore, shearing of a drill pipe subjected to axial tension, compression and buckling, and shearing in flowing well conditions. All these studies are performed and their effect on shearing process is discussed. The effect of high velocity formation fluid through the drill pipe and annulus in the localized shearing region is also assessed separately by performing Computational Fluid Dynamics (CFD) simulations and it is found that the resistance offered by flowing fluid is not significant compared to the high pressure from accumulators required to shear the pipe. A shear ram design accommodating the results of the study is verified for increased efficiency of the shearing process. The study is conducted as part of a Technology Assessment Programs (TAP) for the Bureau of Safety and Environmental Enforcement (BSEE) in the areas of BOP stack sequencing, monitoring and kick detection.
Rigid subsea jumper systems are typically used as interface between subsea structures and are required to accommodate significant static and dynamic loads. Due to constraints imposed by in-line planar jumpers (e.g. U shaped and M shaped jumpers), the industry is shifting towards the use of multi-planar jumper systems (e.g., Z-shaped jumpers). These multi-planar jumper systems have increased tolerance to end displacements and can be tailored to accommodate cyclic end motions of subsea structures. Multi-planar systems, however, come with unique challenges of their own including the coupling of flexural and torsional responses under vortex induced vibrations (VIV), fluid induced vibration (FIV) and slugging. In particular, the development of hydrodynamic slug flow is a common occurrence in oil and gas pipelines. It is understood to be initiated by instabilities of wave on the gas-liquid interface. It is also understood that slug flows are the source of vibration within pipework when a change of direction occurs e.g. 90° bend at a subsea riser base or top side piping. In standard slug flow vibration analysis, averaged slug frequency and length are used to calculate the force generated. In the case of a multi-planar rigid jumper, several changes of direction occur within a short length of pipe. After each bend the characteristics of the slug flow are modified. It is necessary to accurately capture these changes in order to reproduce the forces generated at critical points along the jumper length. This paper presents a methodology for analyzing slugging induced fatigue that has been developed in an on-going study undertaken by MCS Kenny for design of multi-planar rigid jumper systems. In this methodology, Computational Fluid Dynamics (CFD) is used to accurately simulate the flow within the jumper and provide pressure fluctuations on the internal pipe wall for the vibration analysis. The pressure fluctuations are then incorporated in a Finite Element (FE) model of the jumper system and further used to determine the slugging fatigue damage. CFD (Star-ccm+) and FE (Flexcom, ABAQUS) software programs are used to accurately capture the response of the jumper system. Key conclusions and challenges overcome during the course of this study are presented herein.
A Blowout Preventer (BOP) consists of several sets of shear rams stacked together out of which Blind Shear Rams (BSR) is a very critical component to achieve complete shearing of drill pipe. The current study focusses on developing a methodology to model the shearing process and validate it with the shop test. Shop tests were conducted to shear a drill pipe using a surface BOP to obtain the maximum shearing force, shape of sheared drill pipes, shearing time etc. The shear rams used in the test are laser scanned and used in FEA simulations. The FEA model is developed such that it replicates the shop test and simulations are performed using Abaqus Explicit finite element solver. The output from simulations and shop test are compared and found to be in good agreement. The developed methodology is further verified by applying it for shearing different drill pipe sizes and the output is compared with the available data and found to be comparative which proves that the methodology can be implemented for various shearing studies. Original Equipment Manufacturer (OEM) formulas are currently being used in industry to compute the maximum shearing force required to shear the drill pipe under various scenarios. The OEM shearing force is computed for the model under consideration and compared with the shop test and simulation and is found to be conservative. The validated model can be used for conducting studies that provide information on the governing parameters in terms of loading or positioning of the drill pipe to be considered in shear ram designs. This study provides a tool for optimizing the preliminary design of new shear rams and can contribute to more reliable and efficient shear ram design. The study is conducted as part of a Technology Assessment Programs (TAP) for the Bureau of Safety and Environmental Enforcement (BSEE) in the areas of BOP stack sequencing, monitoring and kick detection.
When a current impacts on a circular pipe, fluctuating forces are created due to vortex-shedding in the wake. In offshore industry the interest for vortex induced vibration (VIV) is focused on the fatigue that pipe can experience. The fatigue due to VIV can be the dominant fatigue in some pipelines, subsea structures and risers.The assessment of VIV fatigue for pipelines and subsea structures involves two steps. The step one is to determine the structures response under the combined current and/or wave conditions, using analytical, semi-analytical or numerical approach. The second step is to identify the hot spots in the structure and process their loading states to calculate the corresponding damage or life, such as using S-N curve, which is a common practice in the industry. Since simulating the structures response under fluid loads is the key challenge in the VIV fatigue assessment, this paper focuses on the first step with an emphasis on the FSI approach.The current study developed a finite element model in the frame work of the ABAQUS that can be used in the cross flow VIV analysis of the pipelines and jumpers. The fully three dimensional computational fluid dynamics (CFD) solutions are combined with structural models of pipeline and jumper to predict vortex induced motion. The use of three dimensional CFD solutions is aimed to eliminate the guess work for VIV analysis. The proposed method uses finite element methods that are tolerant of sparse meshes and high element aspect ratios. This allows economical solutions of large fluid domains while retaining the important features of the large fluid vortex structures. The method can also be extended to sheared currents whose velocity varies with depth. The proposed method is applied to pipeline and jumper and benchmarked against published results. It also confirms the validity of the simplification of a jumper to a straight pipe during jumper VIV analysis based on DNV RP-F105, which is a common practice in offshore industry. The developed model might be used to reduce the conservatism in the fatigue assessments of pipeline guided by codes, such as DNV RP-F105.
The deepwater drilling industry has been rocked by the tragic Deepwater Horizon event in the Gulf of Mexico. The incident identified a number of possible failings by operator, service contractors and the regulator which combined to lead to the ultimate results which were evident in mid 2010. This paper will assess the options available to the deepwater drilling industry in assessing the risk of various riser and BOP configurations for drilling and completing deepwater wells in moderate metocean environments. The paper will address two different systems:1. A classic subsea BOP stack configuration, 2. A surface BOP stack with a subsea isolation device (SID). Both of these configurations have merits depending upon a number of factors which include rig availability and schedule, project economics, riser integrity, BOP configuration, geological issues and, most importantly, the hazard and risks associated with each concept. This paper will identify the various technical analyses and risk analysis techniques that must be undertaken to assure the operator of the system is comfortable with each system. These include riser analysis, rig mooring and station keeping analyses, system HAZIDs and HAZOPs, and more. The idea of the paper is to provide the operator and drilling contractor with a 'road map' which will allow them to navigate their way through the various issues to be addressed. This road map will start with the concept stage (rig contracting early well planning) where issues such as project economics, rig availability and risk tolerance will provide input into the overall decision making process. The paper will next address the preliminary and detailed design stages where issues surrounding metocean criteria, rig characteristics and rig configuration and geological conditions will play a part in the overall input. The paper will describe how a project team would approach the issues. Finally as the project moves to the implementation stage the paper will describe the techniques for final assurance that the concept can be managed in the implementation stage.
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