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Guttorm Grytoyr - One of the best experts on this subject based on the ideXlab platform.
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wellhead fatigue analysis method
ASME 2011 30th International Conference on Ocean Offshore and Arctic Engineering, 2011Co-Authors: Lorents Reinås, Torfinn Hørte, Morten Saether, Guttorm GrytoyrAbstract:Re-completion and re-Drilling of existing wells and introduction of new large Drilling rig systems are elements that have led to renewed focus on the fatigue capacity for existing and new Subsea wells. Due to lack of applicable codes and standards for such fatigue calculations, a unified analysis methodology has been developed and described in a Wellhead Fatigue Analysis Method Statement (MS). The intention of this work is to reflect the best practice in the industry and to provide an important contribution to well integrity management. The analysis methodology is limited to fatigue damage from dynamic riser loads present during Subsea Drilling and work over operations. The analysis procedure may be divided into three parts. i) A local response analysis that includes a detailed finite element model from wellhead datum and below. Interaction between the structural well components and soil structure interaction is properly accounted for. The main result from this analysis is the load-to-stress curve that describes the relationship between the riser loads at the wellhead datum and the stress at the fatigue hot spots. The analysis also provides the lower boundary conditions of the global load analysis model. ii) A global load analysis where the floating mobile Drilling unit (MODU) motions and wave loads on the riser are taken into account. The results are time series or load histograms of the loads at wellhead datum, with focus on the bending moment, in all relevant environmental sea states. iii) Fatigue damage assessment, where a mapping of the loads with the relevant load to stress curve is carried out together with subsequent fatigue damage calculation. Appropriate S-N curve is applied together with wave scatter diagrams for the relevant operations and durations. The final result is the accumulated fatigue damage. With a unified analysis methodology in place particular attention is placed on a structured and specified analysis input and output. Results are suggested presented as a function of time and also as a function of key analysis input parameters that are associated with uncertainty. These are prerequisites from a well integrity management perspective in ensuring analysis results that are comparable. This paper presents the essence of the Wellhead Fatigue Analysis Method that was developed in cooperation between Statoil and DNV. Currently this analysis methodology is under extension and revision in the joint industry project (JIP) “Structural Well Integrity During Well Operations”. 11 operators participate in this JIP which also has structured cooperation with equipment suppliers, Drilling companies and analysis houses. The aim is to form a wellhead analysis recommended practice document.Copyright © 2011 by ASME
Lorents Reinås - One of the best experts on this subject based on the ideXlab platform.
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Structural Reliability Analysis Method for Assessing the Fatigue Capacity of Subsea Wellhead Connectors
Volume 2B: Structures Safety and Reliability, 2020Co-Authors: Torfinn Hørte, Lorents Reinås, Anders Wormsen, Andreas Buvarp Aardal, Per GustafssonAbstract:Abstract Subsea Wellheads are the male part of an 18 3/4” bore connector used for connecting Subsea components such as Drilling BOP, XT or Workover systems equipped with a female counterpart — a wellhead connector. Subsea wellheads have an external locking profile for engaging a preloaded wellhead connector with matching internal profile. As such connection is made Subsea, a metal-to-metal sealing is obtained, and a structural conduit is formed. The details of the Subsea wellhead profile are specified by the wellhead user and the standardized H4 hub has a widespread use. In terms of well integrity, the wellhead connector is a barrier element during both well construction (Drilling) activities and life of field (production). Due to the nature of Subsea Drilling operations, a wellhead connector will be subjected to external loads. Fatigue and plastic collapse due to overload are therefore two potential failure modes. These two failure modes are due to the cyclic nature of the loads and the potential for accidental and extreme single loads respectively. The safe load the wellhead connector can sustain without failure can be established by deterministic structural capacity methods. This paper outlines how a generic and probabilistic engineering method; Structural Reliability Analysis, can be applied to a Subsea wellhead connector to estimate the probability of fatigue failure (PoF). As the wellhead connector is a mechanism consisting of a plurality of parts the load effect from cyclic external loads is influenced by uncertainty in friction, geometry and pre-load. Further, there is a inter dependence between these parameters that complicates the problem. In addition to these uncertainties, uncertainties in the fatigue loading itself (from rig and riser) is also accounted for. This paper presents results from applications of Structural Reliability Analysis (SRA) to a wellhead connector and provides experiences and learnings from this case work.
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Risk Based Integrity Assessment and Life Extension Procedure for Subsea Wellhead Connectors
Volume 2B: Structures Safety and Reliability, 2020Co-Authors: G. Sigurdsson, Torfinn Hørte, Anders Wormsen, Michael Macke, Lorents ReinåsAbstract:Abstract Subsea Wellheads are the male part of an 18 3/4” bore connector used for connecting Subsea components such as Drilling BOP, XT or Workover systems equipped with a female counterpart — a wellhead connector. Subsea wellheads have an external locking profile for engaging a preloaded wellhead connector with matching internal profile. When the connector is locked Subsea a metal-to-metal sealing is obtained and a structural conduit is formed. The details of the Subsea wellhead profile are specified by the wellhead user and the standarisedH4 hub has a widespread use. In terms of well integrity, the wellhead connector is a barrier element during both well construction (Drilling) activities and life of field (production). Due to the nature of Subsea Drilling operations a wellhead connector will be subjected to external loads. Fatigue and plastic collapse are therefore two potential failure modes. These two failure modes are due to the cyclic nature of the loads and the potential for accidental and extreme single loads respectively. Establishing the safe load level that the wellhead connector has structural capacity to handle without failure can be done by deterministic engineering methods. Similarly, a deterministic calculated safe fatigue life is the use limit preventing fatigue failure, assuming no inspections. Probabilistic engineering method; Structural Reliability Analysis (SRA), can be applied to a Subsea wellhead connector to establish the probability of fatigue failure (PoF). Risk Based Inspection (RBI) is a probabilistic analysis procedure that requires quantified PoF and Consequence of Failure (CoF). The RBI outcome may be used to optimized inspection plans to ensure a safe PoF target level. The RBI methodology is widely accepted, and guidance can be found in several standards. Subsea wellheads are normally classified as un-inspectable. During Drilling operations commencement, the uppermost section of the wellhead (high pressure housing including H4 hub profile) will be visible and accessible thus allowing for inspection. This uppermost section may also accessible for inspection when a wellhead connector is locked on. From an SRA basis a generic RBI procedure applicable to Subsea wellheads are proposed and established for a generic case of a 27” mandrel with a H4 hub. This paper then proceeds to providing the maximum non detectable flaw size performance required for a wellhead inspection tool/method to be efficient. The importance of accidental load and cyclic load magnitude and uncertainty is shown to impact this conclusion. The potential inspectional value of performing BOP connector leak test at regular intervals during the Drilling operation has also been investigated and shown to be conditionally limited. This paper proposes a procedure for application of RBI to the problem of achieving life extension of a wellhead external locking profile while connected to a wellhead connector. The objective is to propose minimum performance requirements for the inspection tool/method to be efficient. Finally, the potential impact of RBI results in a well integrity risk assessment is covered.
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wellhead fatigue analysis method
ASME 2011 30th International Conference on Ocean Offshore and Arctic Engineering, 2011Co-Authors: Lorents Reinås, Torfinn Hørte, Morten Saether, Guttorm GrytoyrAbstract:Re-completion and re-Drilling of existing wells and introduction of new large Drilling rig systems are elements that have led to renewed focus on the fatigue capacity for existing and new Subsea wells. Due to lack of applicable codes and standards for such fatigue calculations, a unified analysis methodology has been developed and described in a Wellhead Fatigue Analysis Method Statement (MS). The intention of this work is to reflect the best practice in the industry and to provide an important contribution to well integrity management. The analysis methodology is limited to fatigue damage from dynamic riser loads present during Subsea Drilling and work over operations. The analysis procedure may be divided into three parts. i) A local response analysis that includes a detailed finite element model from wellhead datum and below. Interaction between the structural well components and soil structure interaction is properly accounted for. The main result from this analysis is the load-to-stress curve that describes the relationship between the riser loads at the wellhead datum and the stress at the fatigue hot spots. The analysis also provides the lower boundary conditions of the global load analysis model. ii) A global load analysis where the floating mobile Drilling unit (MODU) motions and wave loads on the riser are taken into account. The results are time series or load histograms of the loads at wellhead datum, with focus on the bending moment, in all relevant environmental sea states. iii) Fatigue damage assessment, where a mapping of the loads with the relevant load to stress curve is carried out together with subsequent fatigue damage calculation. Appropriate S-N curve is applied together with wave scatter diagrams for the relevant operations and durations. The final result is the accumulated fatigue damage. With a unified analysis methodology in place particular attention is placed on a structured and specified analysis input and output. Results are suggested presented as a function of time and also as a function of key analysis input parameters that are associated with uncertainty. These are prerequisites from a well integrity management perspective in ensuring analysis results that are comparable. This paper presents the essence of the Wellhead Fatigue Analysis Method that was developed in cooperation between Statoil and DNV. Currently this analysis methodology is under extension and revision in the joint industry project (JIP) “Structural Well Integrity During Well Operations”. 11 operators participate in this JIP which also has structured cooperation with equipment suppliers, Drilling companies and analysis houses. The aim is to form a wellhead analysis recommended practice document.Copyright © 2011 by ASME
Christine Ehlig-economides - One of the best experts on this subject based on the ideXlab platform.
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An Innovative Ultradeepwater Subsea Blowout Preventer Control System Using Shape-Memory Alloy Actuators
Journal of Energy Resources Technology-transactions of The Asme, 2008Co-Authors: Gangbing Song, Ziping Hu, Ning Ma, Michael J. Economides, Samuel Robello, Christine Ehlig-economidesAbstract:This paper presents an innovative undersea blowout preventer (BOP) using shape-memory alloy (SMA). The new device using SMA actuators could easily be implemented into existing conventional Subsea control system so that they can work solely or as a backup of other methods. Most important, the innovative all-electric BOP will provide much faster response than its hydraulic counterpart and will improve safety for Subsea Drilling. To demonstrate the feasibility of such a device, a proof-of-concept prototype of a pipe RAM type BOP with SMA actuation has been designed, fabricated, and tested at the University of Houston. The BOP actuator uses strands of SMA wires to achieve large force and large displacement in a remarkably small space. Experimental results demonstrate that the BOP can be activated and fully closed in less than 10s. The concept of this innovative device is illustrated, and detailed comparisons of the response time for hydraulic and nitinol SMA actuation mechanisms are included. This preliminary research reveals the potential of smart material technology in Subsea Drilling systems.
Reinås Lorents - One of the best experts on this subject based on the ideXlab platform.
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Wellhead Fatigue Analysis : Surface casing cement boundary condition for Subsea wellhead fatigue analytical models
University of Stavanger Norway, 2012Co-Authors: Reinås LorentsAbstract:PhD thesis in Petroleum engineeringMaterial fatigue is a failure mode that has been known to researchers and engineers since the 19th century. Catastrophic accidents have happened due to fatigue failures of structures, machinery and transport vehicles. The capsizing of the semisubmersible rig Alexander L. Kielland in Norwegians waters in 1980 killed 123 people, and investigations pointed at the fatigue failure of a weld as one of the direct causes. This accident led to a number of improvements to the design of offshore structures. The noticeable safety principle ”No single accident should lead to escalating consequences” has since been adopted in a widespread manner. Since 1992 the Petroleum Safety Authority in Norway has enforced a risk based safety regime. Wells are designed to hold back reservoir pressures and avoid uncontrolled escape of hydrocarbons. In other words a well is a pressure containing vessel. Norwegian safety regulations require a dual barrier construction of wells. This safety principle ensures that one “barrier” is preventing an escalating situation should the other barrier fail. A wellhead is a heavy walled pressure vessel placed at the top of the well. The wellhead is part of the second well barrier envelope during Drilling. The Subsea wellheads are located at sea bottom and during Subsea Drilling the Blow Out Preventer (BOP) is placed on top of the Subsea wellhead. The Drilling riser is the connection between the BOP and the floating Drilling unit. Waves and current forces acting on the Drilling riser and Drilling unit will cause dynamic movement. Flexible joints at top and bottom of the Drilling riser protects the Drilling riser from localised bending moments. The Subsea wellhead is both a pressure vessel and a structurally load bearing component resisting external loads transmitted from a connected riser. These external loads can be static and cyclic combinations of bending and tension (compression). Cyclic loads will cause fatigue damage to the well. The well can take a certain amount of fatigue damage without failing. A fatigue failure of a WH system may have serious consequences. Should the WH structurally fail its pressure vessel function will be lost and for this reason WH fatigue is a potential threat to well integrity. The structural load bearing function will also be affected. Wellhead fatigue analysis can be used as a tool to estimate the accumulated fatigue damage. Analysis results then compares to a safe fatigue limit. This thesis addresses selected aspects of fatigue damage estimations of Subsea wellheads and surface casings. The presented work is a contribution to the fatigue analysis methodology currently being developed within the industry. The well cement role as a boundary condition for surface casings in analytical models is particularly addressed. The majority of research focuses on the casing shoe and formation sealing, which is the primary objective of well cementing. Recent research focus on the cement limits conditions e.g. elevated temperatures. The “near-seabed” conditions of lead cements have seen less scrutiny. Some researchers have shown interest in this issue related to deep water cementing. Deep water bottom temperature is low all year round regardless of location latitude. Low sea water temperatures will depress the normal thermal gradient of the upper parts of the soil. Subsea wells are typically cemented using a lead and tail cement system, and the lead top casing cement will be pumped all the way to seabed. This lead cement will then be left curing in a low temperature environment. Hydration of cement is an exothermic chemical reaction, and the reaction rate is dependent on temperature. Laboratory measurements of low temperature early compressive strength of typical lead cement slurries are presented herein. In the North Sea the duration between placement of surface casing lead cement and installation of BOP/Drilling riser will typical be around 24 hrs. Then dynamic riser loads will start acting on the upper part of a Subsea well. Bending of the well causes relative motions between the conductor and surface casing. The cement around these casings will experience these relative motions. The combination of delayed cement setting due to low temperature and surface casing motions will cause localized failure of cement bonding in the upper part of the well. In Subsea wellhead fatigue analysis finite element models are used. Boundary conditions in analytical models are important in ensuring similar behaviour of model and reality. One boundary condition in wellhead models is the lateral cement support of the surface casing. Modelling this cement support as infinitely stiff with a discrete vertical transition is the existing solution. In this work a modified boundary condition is presented based on low curing temperatures in combination with “premature” loading of the supporting cement. An overall analysis methodology approach has been suggested. Using a detailed local model of the well to define the lower boundary condition for the global riser load analytical model is one of its features. The implementation of a modified cement boundary condition will change the global stiffness of the local well model. The possible effect on global riser load from variations to the lower boundary condition has been studied. The conclusion supports the suggested analysis approach. Overall well ultimate structural strength will be reduced by the presence of a fatigue crack in a non pressurised load bearing part of a Subsea well. An analysis methodology with case results are presented and indicate that the location of a fatigue crack affects the reduction in ultimate strength. Cases of significant reduction are expected to impact normal operating limitations. To be able to include the wellhead fatigue failure mode in an overall risk management system, the failure probability needs to be estimated. This can be done by applying a structural reliability analysis methodology to the problem. A suggested structural analysis methodology approach is suggested and notational failure probabilities are presented. Future improvements to wellhead fatigue analysis may emerge from calibrations from measurements of the reality. A comparison between analytical fatigue loading and measured fatigue loading has been presented and results indicate that the analysis results are conservative. This is evidence that analytical estimate on acceptable fatigue limits can be trusted from a safety point of view. It also indicates the monetary potential that measurements can present to the well
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Wellhead Fatigue Analysis : Surface casing cement boundary condition for Subsea wellhead fatigue analytical models
University of Stavanger Norway, 2012Co-Authors: Reinås LorentsAbstract:Material fatigue is a failure mode that has been known to researchers and engineers since the 19th century. Catastrophic accidents have happened due to fatigue failures of structures, machinery and transport vehicles. The capsizing of the semisubmersible rig Alexander L. Kielland in Norwegians waters in 1980 killed 123 people, and investigations pointed at the fatigue failure of a weld as one of the direct causes. This accident led to a number of improvements to the design of offshore structures. The noticeable safety principle ”No single accident should lead to escalating consequences” has since been adopted in a widespread manner. Since 1992 the Petroleum Safety Authority in Norway has enforced a risk based safety regime. Wells are designed to hold back reservoir pressures and avoid uncontrolled escape of hydrocarbons. In other words a well is a pressure containing vessel. Norwegian safety regulations require a dual barrier construction of wells. This safety principle ensures that one “barrier” is preventing an escalating situation should the other barrier fail. A wellhead is a heavy walled pressure vessel placed at the top of the well. The wellhead is part of the second well barrier envelope during Drilling. The Subsea wellheads are located at sea bottom and during Subsea Drilling the Blow Out Preventer (BOP) is placed on top of the Subsea wellhead. The Drilling riser is the connection between the BOP and the floating Drilling unit. Waves and current forces acting on the Drilling riser and Drilling unit will cause dynamic movement. Flexible joints at top and bottom of the Drilling riser protects the Drilling riser from localised bending moments. The Subsea wellhead is both a pressure vessel and a structurally load bearing component resisting external loads transmitted from a connected riser. These external loads can be static and cyclic combinations of bending and tension (compression). Cyclic loads will cause fatigue damage to the well. The well can take a certain amount of fatigue damage without failing. A fatigue failure of a WH system may have serious consequences. Should the WH structurally fail its pressure vessel function will be lost and for this reason WH fatigue is a potential threat to well integrity. The structural load bearing function will also be affected. Wellhead fatigue analysis can be used as a tool to estimate the accumulated fatigue damage. Analysis results then compares to a safe fatigue limit. This thesis addresses selected aspects of fatigue damage estimations of Subsea wellheads and surface casings. The presented work is a contribution to the fatigue analysis methodology currently being developed within the industry. The well cement role as a boundary condition for surface casings in analytical models is particularly addressed. The majority of research focuses on the casing shoe and formation sealing, which is the primary objective of well cementing. Recent research focus on the cement limits conditions e.g. elevated temperatures. The “near-seabed” conditions of lead cements have seen less scrutiny. Some researchers have shown interest in this issue related to deep water cementing. Deep water bottom temperature is low all year round regardless of location latitude. Low sea water temperatures will depress the normal thermal gradient of the upper parts of the soil. Subsea wells are typically cemented using a lead and tail cement system, and the lead top casing cement will be pumped all the way to seabed. This lead cement will then be left curing in a low temperature environment. Hydration of cement is an exothermic chemical reaction, and the reaction rate is dependent on temperature. Laboratory measurements of low temperature early compressive strength of typical lead cement slurries are presented herein. In the North Sea the duration between placement of surface casing lead cement and installation of BOP/Drilling riser will typical be around 24 hrs. Then dynamic riser loads will start acting on the upper part of a Subsea well. Bending of the well causes relative motions between the conductor and surface casing. The cement around these casings will experience these relative motions. The combination of delayed cement setting due to low temperature and surface casing motions will cause localized failure of cement bonding in the upper part of the well. In Subsea wellhead fatigue analysis finite element models are used. Boundary conditions in analytical models are important in ensuring similar behaviour of model and reality. One boundary condition in wellhead models is the lateral cement support of the surface casing. Modelling this cement support as infinitely stiff with a discrete vertical transition is the existing solution. In this work a modified boundary condition is presented based on low curing temperatures in combination with “premature” loading of the supporting cement. An overall analysis methodology approach has been suggested. Using a detailed local model of the well to define the lower boundary condition for the global riser load analytical model is one of its features. The implementation of a modified cement boundary condition will change the global stiffness of the local well model. The possible effect on global riser load from variations to the lower boundary condition has been studied. The conclusion supports the suggested analysis approach. Overall well ultimate structural strength will be reduced by the presence of a fatigue crack in a non pressurised load bearing part of a Subsea well. An analysis methodology with case results are presented and indicate that the location of a fatigue crack affects the reduction in ultimate strength. Cases of significant reduction are expected to impact normal operating limitations. To be able to include the wellhead fatigue failure mode in an overall risk management system, the failure probability needs to be estimated. This can be done by applying a structural reliability analysis methodology to the problem. A suggested structural analysis methodology approach is suggested and notational failure probabilities are presented. Future improvements to wellhead fatigue analysis may emerge from calibrations from measurements of the reality. A comparison between analytical fatigue loading and measured fatigue loading has been presented and results indicate that the analysis results are conservative. This is evidence that analytical estimate on acceptable fatigue limits can be trusted from a safety point of view. It also indicates the monetary potential that measurements can present to the well
Torfinn Hørte - One of the best experts on this subject based on the ideXlab platform.
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Structural Reliability Analysis Method for Assessing the Fatigue Capacity of Subsea Wellhead Connectors
Volume 2B: Structures Safety and Reliability, 2020Co-Authors: Torfinn Hørte, Lorents Reinås, Anders Wormsen, Andreas Buvarp Aardal, Per GustafssonAbstract:Abstract Subsea Wellheads are the male part of an 18 3/4” bore connector used for connecting Subsea components such as Drilling BOP, XT or Workover systems equipped with a female counterpart — a wellhead connector. Subsea wellheads have an external locking profile for engaging a preloaded wellhead connector with matching internal profile. As such connection is made Subsea, a metal-to-metal sealing is obtained, and a structural conduit is formed. The details of the Subsea wellhead profile are specified by the wellhead user and the standardized H4 hub has a widespread use. In terms of well integrity, the wellhead connector is a barrier element during both well construction (Drilling) activities and life of field (production). Due to the nature of Subsea Drilling operations, a wellhead connector will be subjected to external loads. Fatigue and plastic collapse due to overload are therefore two potential failure modes. These two failure modes are due to the cyclic nature of the loads and the potential for accidental and extreme single loads respectively. The safe load the wellhead connector can sustain without failure can be established by deterministic structural capacity methods. This paper outlines how a generic and probabilistic engineering method; Structural Reliability Analysis, can be applied to a Subsea wellhead connector to estimate the probability of fatigue failure (PoF). As the wellhead connector is a mechanism consisting of a plurality of parts the load effect from cyclic external loads is influenced by uncertainty in friction, geometry and pre-load. Further, there is a inter dependence between these parameters that complicates the problem. In addition to these uncertainties, uncertainties in the fatigue loading itself (from rig and riser) is also accounted for. This paper presents results from applications of Structural Reliability Analysis (SRA) to a wellhead connector and provides experiences and learnings from this case work.
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Risk Based Integrity Assessment and Life Extension Procedure for Subsea Wellhead Connectors
Volume 2B: Structures Safety and Reliability, 2020Co-Authors: G. Sigurdsson, Torfinn Hørte, Anders Wormsen, Michael Macke, Lorents ReinåsAbstract:Abstract Subsea Wellheads are the male part of an 18 3/4” bore connector used for connecting Subsea components such as Drilling BOP, XT or Workover systems equipped with a female counterpart — a wellhead connector. Subsea wellheads have an external locking profile for engaging a preloaded wellhead connector with matching internal profile. When the connector is locked Subsea a metal-to-metal sealing is obtained and a structural conduit is formed. The details of the Subsea wellhead profile are specified by the wellhead user and the standarisedH4 hub has a widespread use. In terms of well integrity, the wellhead connector is a barrier element during both well construction (Drilling) activities and life of field (production). Due to the nature of Subsea Drilling operations a wellhead connector will be subjected to external loads. Fatigue and plastic collapse are therefore two potential failure modes. These two failure modes are due to the cyclic nature of the loads and the potential for accidental and extreme single loads respectively. Establishing the safe load level that the wellhead connector has structural capacity to handle without failure can be done by deterministic engineering methods. Similarly, a deterministic calculated safe fatigue life is the use limit preventing fatigue failure, assuming no inspections. Probabilistic engineering method; Structural Reliability Analysis (SRA), can be applied to a Subsea wellhead connector to establish the probability of fatigue failure (PoF). Risk Based Inspection (RBI) is a probabilistic analysis procedure that requires quantified PoF and Consequence of Failure (CoF). The RBI outcome may be used to optimized inspection plans to ensure a safe PoF target level. The RBI methodology is widely accepted, and guidance can be found in several standards. Subsea wellheads are normally classified as un-inspectable. During Drilling operations commencement, the uppermost section of the wellhead (high pressure housing including H4 hub profile) will be visible and accessible thus allowing for inspection. This uppermost section may also accessible for inspection when a wellhead connector is locked on. From an SRA basis a generic RBI procedure applicable to Subsea wellheads are proposed and established for a generic case of a 27” mandrel with a H4 hub. This paper then proceeds to providing the maximum non detectable flaw size performance required for a wellhead inspection tool/method to be efficient. The importance of accidental load and cyclic load magnitude and uncertainty is shown to impact this conclusion. The potential inspectional value of performing BOP connector leak test at regular intervals during the Drilling operation has also been investigated and shown to be conditionally limited. This paper proposes a procedure for application of RBI to the problem of achieving life extension of a wellhead external locking profile while connected to a wellhead connector. The objective is to propose minimum performance requirements for the inspection tool/method to be efficient. Finally, the potential impact of RBI results in a well integrity risk assessment is covered.
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wellhead fatigue analysis method
ASME 2011 30th International Conference on Ocean Offshore and Arctic Engineering, 2011Co-Authors: Lorents Reinås, Torfinn Hørte, Morten Saether, Guttorm GrytoyrAbstract:Re-completion and re-Drilling of existing wells and introduction of new large Drilling rig systems are elements that have led to renewed focus on the fatigue capacity for existing and new Subsea wells. Due to lack of applicable codes and standards for such fatigue calculations, a unified analysis methodology has been developed and described in a Wellhead Fatigue Analysis Method Statement (MS). The intention of this work is to reflect the best practice in the industry and to provide an important contribution to well integrity management. The analysis methodology is limited to fatigue damage from dynamic riser loads present during Subsea Drilling and work over operations. The analysis procedure may be divided into three parts. i) A local response analysis that includes a detailed finite element model from wellhead datum and below. Interaction between the structural well components and soil structure interaction is properly accounted for. The main result from this analysis is the load-to-stress curve that describes the relationship between the riser loads at the wellhead datum and the stress at the fatigue hot spots. The analysis also provides the lower boundary conditions of the global load analysis model. ii) A global load analysis where the floating mobile Drilling unit (MODU) motions and wave loads on the riser are taken into account. The results are time series or load histograms of the loads at wellhead datum, with focus on the bending moment, in all relevant environmental sea states. iii) Fatigue damage assessment, where a mapping of the loads with the relevant load to stress curve is carried out together with subsequent fatigue damage calculation. Appropriate S-N curve is applied together with wave scatter diagrams for the relevant operations and durations. The final result is the accumulated fatigue damage. With a unified analysis methodology in place particular attention is placed on a structured and specified analysis input and output. Results are suggested presented as a function of time and also as a function of key analysis input parameters that are associated with uncertainty. These are prerequisites from a well integrity management perspective in ensuring analysis results that are comparable. This paper presents the essence of the Wellhead Fatigue Analysis Method that was developed in cooperation between Statoil and DNV. Currently this analysis methodology is under extension and revision in the joint industry project (JIP) “Structural Well Integrity During Well Operations”. 11 operators participate in this JIP which also has structured cooperation with equipment suppliers, Drilling companies and analysis houses. The aim is to form a wellhead analysis recommended practice document.Copyright © 2011 by ASME
