Paul Jukes

Extra High-Pressure High-Temperature (XHPHT) Flowlines: Design Considerations and Challenges

Development of deep water oil reservoirs in the Gulf of Mexico may encounter conditions where the flowline product temperatures approach 177°C (350°F), water depths range to 3000 m (10,000 ft), and tie-back distances up to 40 miles are presently being considered. These high flowline temperatures, water depths and distances, present real challenges to the design of flowlines. The objective of this paper is to present the design considerations and challenges of designing for extra high pressure high temperature (XHPHT) conditions. For such conditions, a pipe-in-pipe (PIP) flowline system with thermal expansion management, and a limit state-based design are viable solutions. This paper is split into three main parts and covers (i) design challenges and how they are overcome, (ii) finite element analysis design methods, and (iii) qualification testing of PIP components. The first section presents the main design issues, and challenges, of designing flowlines for deepwater and high-temperature conditions. The paper discusses aspects of controlling the large axial loads, such as thermal expansion management using buckle initiators and end constraints for flowlines, and presents current methods. The second section describes the use of advanced finite element analysis (FEA) tools for the design and simulation of PIP systems, and presents local and global FEA models, using ABAQUS, to investigate the limit state design of XHPHT flowlines. A 3-D helical response of the inner pipe subjected to high temperature, and the sequential reeling and lateral buckling of flowlines is also discussed. The final section of the paper describes the qualification testing to be undertaken on PIP components to ensure structural integrity and long-term thermal and structural performance. Qualification testing for PIP components for 177°C (350°F) service is discussed, and includes the testing of centralizers, waterstop seals, thermal insulation and loadshares. This paper is based on both theoretical and practical research work.Copyright

Development and Validation of a Coupled Eulerian Lagrangian Finite Element Ice Scour Model

Pipelines in the arctic offshore must be installed and buried below the seabed to avoid direct contact, and to mitigate the effects of strains induced by soil displacement below the ice keel scour depth. A three-dimensional (3D) finite element (FE) model that utilizes the Coupled Eulerian Lagrangian (CEL) formulation has been developed to provide direct and explicit estimation of pipe stresses and strains. The CEL formulation is novel, and no published work has attempted to explore its capabilities and potential for ice scour modeling to date. The developed model will be helpful in solving some of the uncertainty regarding pipeline burial depth, potentially resulting in major trenching cost savings. In order to gain confidence in this numerical modeling technique, a systematic validation effort was carried out, whereby numerical predictions of subgouge displacements were compared with measured data from centrifuge tests and other published empirical and numerical data. Sensitivity analyses were then performed to investigate the effect of the scouring keel geometry, depth, and attack angle on the induced subgouge soil displacements. Preliminary conclusions were drawn and presented in this paper.Copyright

Upheaval Buckling Analysis of Partially Buried Pipeline Subjected to High Pressure and High Temperature

Offshore industry is now pushing into the deepwater and starting to face the much higher energy reservoir with high pressure and high temperature. Besides the significant impacts on the material, strength, and reliability of the wellhead, tree, and manifold valve; high Pressure (HP) also leads to thicker pipe wall that increases manufacturing and installation cost. High Temperature (HT) can have much wider impact on operation since the whole subsea system has to be operated over a greater temperature range between the non-producing situations such as installation, and long term shut down, and the maximum production flow. It is more concerned for fact that thicker wall pipe results in much greater thermal load so to make the pipeline strength and tie-in designs more challenging. Burying sections of a HPHT pipeline can provide the advantages of thermal insulation by using the soil cover to retain the cool-down time. Burial can also help to achieve high confidence anchoring and additional resistance to the pipeline axial expansion and walking. Upheaval buckling is a major concern for the buried pipelines because it can generate a high level of strain when happens. Excessive yielding can cause the pipeline to fail prematurely. Partial burial can have less concern although it may complicate the pipeline global buckling behavior and impose challenges on the design and analysis. This paper presents the studies on the upheaval buckling of partially buried pipelines, typical example of an annulus flooded pipe-in-pipe (PIP) configuration. The full-scale FE models were created to simulate the pipeline thermal expansion / upheaval / lateral buckling responses. The pipe-soil interaction (PSI) elements were utilized to model the relationship between the soil resistance (force) and the pipe displacement for the buried sections. The effects of soil cover height, vertical prop size, and soil resistance on the upheaval and lateral buckling response of a partially buried pipeline were investigated. This paper presents the latest techniques, allows an understanding in the global buckling, upheaval or lateral, of partially buried pipeline under the HPHT, and assists the industry to pursue safer but cost effective design.Copyright

Comprehensive FEA of Thermal Mitigation Buoyancy Module (TMBM)–Soil Interaction Using the Coupled Eulerian–Lagrangian (CEL) Method

Thermal expansion and global buckling is a critical design aspect for subsea flowline systems subjected to high pressure and high temperature (HPHT). In the Gulf of Mexico, HPHT oil/gas production is becoming exceedingly common as drilling and production depths extend deeper. Advanced finite element analysis becomes essential for flowline expansion and buckling design which is highly dependent on pipe-soil interaction behavior. For decades, pipe-soil interaction has been the focus of many research studies and joint industry projects. For HPHT flowline systems, thermal mitigation is decisive for safe design. Thermal mitigation acts to control global buckling at designate locations and avoid buckling in unknown locations. Thermal mitigation results in significant cost savings by lowering the welding class besides the buckling locations and increases safety in terms of local buckling, fracture, and fatigue. One widely used thermal mitigation method involves attaching a buoyancy module around a segment of the flowline. In this paper the Coupled Eulerian Langrangian (CEL) finite element (FE) formulation is utilized to simulate the interaction between soil and the thermal mitigation buoyancy module (TMBM). The paper demonstrates the capability of the CEL FE method to simulate large soil deformation without the numerical difficulties that are commonly associated with other numerical formulations e.g. ALE (Arbitrary Lagrangian Eulerian) or more conventional Lagrangian. Initially, a three dimensional (3D), continuum, FE model is used to establish the variation of initial embedment along the length of the buoyancy and adjoining pipe. The study then establishes the lateral displacement/resistance relationships under different levels of contact pressure and soil embedment for a series of buoyancy-soil interaction segments, also using the CEL FE method. Current practice for global pipeline thermal expansion FEA is to utilize the same friction model for both buoyancy-soil interaction and pipe-soil interaction. The obtained buoyancy-soil interaction model from the current study is to be used as input to the global FE model to more precisely simulate flowline lateral buckling behavior. This paper presents a practical application of the current state of the art in modeling large soil deformations in providing an improved approach for modeling buoyancy-soil interactions in the global FEA of pipeline thermal expansion and lateral buckling.Copyright

Permafrost Thawing-Pipeline Interaction Advanced Finite Element Model

The increasing energy demand has promoted the interest in exploration and field development in the Arctic waters, which holds one quarter of the world’s petroleum reserves. The harsh conditions and fragile environment in the arctic region introduce many challenges to a sustainable development of these resources. One of the key challenges is the engineering consideration of warm pipelines installed in permafrost areas; found mainly in shallow waters and shore crossings. Evaluations have to be made during the pipeline design to avoid significant thaw settlement and large-scale permafrost degrading. In this paper, a three-dimensional (3D) finite element (FE) model was developed to study the interaction between buried pipelines transporting warm hydrocarbons and the surrounding permafrost. This interaction is a combination of several mechanisms: heat transfer from the pipeline, results in permafrost thawing and formation of thaw bulb around the pipeline. Consequently, the thaw settlement of soil beneath the pipeline base results in bending strains in the pipe wall. For safe operations, the pipe should be designed so that the induced strains do not exceed the ultimate limit state conditions. The developed model helps in accurate prediction of pipe strains by using finite element continuum modeling method as opposed to the more commonly used discrete (springs) modeling and hand calculations. It also assesses the real size of the thaw bulb and the corresponding settlement at any time, thus preventing an over-conservative design.© 2009 ASME

Offshore Pipeline Embedment in Cohesive Soil: A Comparison Between Existing and CEL Solutions

A common issue confronted by engineers in analyzing high pressure high temperature (HPHT) pipelines for installation and operating conditions is pipe-soil interaction. For installation, a key concern is whether the soil can generate sufficient resistance to allow the pipeline to be laid on the curve. For operation, a concern is whether the pipeline structural stress can be controlled and mitigated, for the given soil condition, under conditions of thermal expansion and potential global buckling. In both scenarios, pipeline embedment is a critical parameter as it is directly related to soil resistances to the pipeline stability. Previous studies have used experimental, analytical and numerical methods to provide estimates to the pipe embedment during the laying operation. The recently developed Coupled Eulerian-Lagrange (CEL) finite element analysis (FEA) method provides a promising numerical technique in analyzing large-deformation geotechnical problems, such as pipeline embedment analysis. This paper uses this approach, together with currently available embedment solutions, to cross-validate these methods for cohesive soils.Copyright

From Installation to Operation: A Full-Scale Finite Element Modeling of Deep-Water Pipe-in-Pipe System

Developments of deep water oil reservoirs are presently being considered in the Gulf of Mexico (GoM). Pipe-in-Pipe (PIP) systems are widely used and planned as the tie-back flowline for high pressure and high temperature production (HPHT) due to their exceptional thermal insulation capabilities. The installation of PIP flowline in deep water, disregarding the laying method, can present real challenges because of the PIP string weight. The effect of the lowering displacement as well as the lock-in compressive load acting on the inner pipe for the commonly used un-bonded PIP is also a major concern. Such effects will enhance the total flowline compression when the high temperature and high pressure are applied after start-up; they greatly increase the severity of the global buckling and result in local plastic collapse at a larger bending curvature section or strain localization area. An even greater concern is that industry fails to realize the seriousness of such failure potential, and the PIP is generally treated as a composite single pipe which does not evaluate the PIP load response correctly, especially the inner pipe lock-in compression omitted. It could result in an unsafe design for HPHT production. This paper endeavors to provide a trustworthy solution for the HPHT PIP systems from installation to operation by using the advanced analysis tool — “Simulator”, an ABAQUS based in-house Finite Element Analysis (FEA) engine. “Simulator” allows the PIP pipes being modeled individually with realistic interaction between the pipes. A systematic process was introduced by using a generic deep-water PIP flowline as a working example of J-Lay installation and HPHT production. The load and stress responses of the PIP at all installation stages were calculated with a high level of accuracy, they were then included in the global buckling analysis for the HPHT operation. The study demonstrated the effectiveness of Loadshare, an industry-leading solution; which reduces or eliminates the inner pipe lock-in compression and improves the PIP compressive load capacity for the high temperature operation.Copyright

The technical challenges of designing oil and gas pipelines in the arctic

The world demand of oil and gas is growing at an ever increasing rate, and as a result, there is a demand to explore new areas for more petroleum production. The arctic region is one of the remaining unexplored areas where such exploration still can be done. According to the US Geological Survey estimates, the arctic region, mostly offshore, holds as much as 25% of the worlds untapped reserve of hydrocarbons where much of the reserve is lying under seasonal or year-round sea ice. The exploitation of these remaining reserves, however, will depend upon meeting the technical challenges of design, construction, and operation of offshore installations. Despite some experience with Arctic oil and gas exploration and production during the last three decades, technology gaps still exist and will have to be bridged in order to enable optimized developments to proceed. In this paper, technical design difficulties particular to arctic pipelines are presented; these include ice gouging, permafrost thaw settlement, strudel scour, and upheaval buckling. An emphasis is then placed on advanced finite element techniques that can be used to address these issues, with an example of such techniques illustrating their ability to model highly complex and nonlinear phenomena.

Flow Induced Forces on Multi-Planar Rigid Jumper Systems

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.Copyright

Vibration Assessment Methodology for Subsea Pipework

Vibration is an important cause of fatigue damage in subsea piping systems (jumpers, rigid spools, tree pipework etc.). Presently, guidelines are available for a qualitative and quantitative vibration assessment for process pipework, but these are more applicable to topside and refinery piping. Currently, there are limited guidelines specifically developed for vibration assessment for subsea piping. For subsea pipework, additional guidelines may be necessary to check for possible interaction between current induced VIV, wave induced VIV (for shallow waters) and slugging, and other mechanisms that result in flow induced vibration. This paper provides augmented guidelines for subsea piping, which takes into account the interaction between piping and its subsea environment. At the same time, suggestions are provided to trim the guidelines of mechanisms that does not occur subsea. The Likelihood of Failure (LOF) assessment based on the proposed guidelines provides an indication whether further detailed vibration analysis (such as CFD and/or FEA) is necessary. Based on the LOF from this assessment, suitable detailed analysis can be performed to determine the fatigue life. This enhanced methodology enables the user to perform vibration assessment and analysis in the least computational time by identifying 1) the most critical flow conditions over the production life of the field and 2) the most critical vibration mechanisms that should be analyzed. This results in a reduction in the number of conditions or load cases which require detailed analysis, without decreasing the accuracy of the assessment and analysis.Copyright