Casing Collapse Design Using Structural Reliability Analysis for a Subsea Well on the Norwegian Continental Shelf

2018 ◽  
Author(s):  
David Buchmiller ◽  
Arve Bjørset ◽  
Torfinn Hørte ◽  
Sune Pettersen
Keyword(s):  
Finite Element ◽  
Reliability Analysis ◽  
Structural Reliability ◽  
Probability Of Failure ◽  
Critical Parameters ◽  
Safety Level ◽  
Structural Reliability Analysis ◽  
Specific Input ◽  
Well Design ◽  
Casing Collapse

Casing collapse capacity was identified by Statoil as a critical operational parameter on one of its fields in production. This facilitated the need to re-evaluate the overall well design, specifically the production casing’s collapse capacity. Studies were performed to analyze and objectively increase the documented casing collapse capacity, while maintaining the safety level. Initially, the casing collapse capacity was evaluated using API TR 5C3 / ISO 10400, with insufficient capacity being documented. In order to investigate further, physical material testing and collapse testing were performed. Detailed finite element analysis was used to evaluate the casing collapse capacity, given well specific input parameters. The four critical parameters of axial load, casing ovality, casing wear, and temperature-dependent material properties were identified and the importance of each parameter was mapped. Using the testing results and the finite element models as a basis, structural reliability analysis (SRA) was applied to calculate the probability of failure for casing collapse of the production casing as a function of the differential pressure. The SRA provided results for the spread of the field and for individual wells given specific input on the key parameters of casing ovality, wear and temperature. At the selected target reliability level, the SRA results showed a higher collapse capacity of the production casing relative to conservative calculations commonly used from API TR 5C3 / ISO 10400 for well design. Applying SRA to well design, specifically collapse evaluations, has proven useful in concluding on the probability of failure. The SRA has transformed improved knowledge from testing and measurements to reduced uncertainty and a corresponding reduction in the failure probability. The potential over-conservatism in the conventional deterministic analysis is then avoided, while maintaining the overall safety level. The SRA results were used to assist in the risk evaluation resulting in an allowance for continued production on existing wells.

Benefit From Structural Reliability Analysis in Risk Evaluation of Collapse of Externally Supported Casing

2020 ◽  
Author(s):  
Torfinn Hørte ◽  
Arve Bjørset ◽  
Dan Tudor Zaharie ◽  
Sune Pettersen
Keyword(s):  
Reliability Analysis ◽  
Risk Evaluation ◽  
Structural Reliability ◽  
External Support ◽  
Good Correspondence ◽  
Operational Parameter ◽  
Structural Reliability Analysis ◽  
Fe Simulations ◽  
Well Design ◽  
Casing Collapse

Abstract Casing collapse capacity was identified by Equinor as a critical operational parameter on one of its fields in production. This led to re-evaluation and detailed studies of the overall well design, specifically the production casing’s collapse capacity, together with consequence and risk evaluations in case of a potential casing failure. As an important and useful input to the risk evaluations, the present paper presents a structural reliability analysis for casing collapse. Initially, the casing collapse capacity was evaluated using API TR 5C3 / ISO 10400 [1], with insufficient capacity being documented. In order to investigate further, physical material testing and collapse testing were performed. Two kinds of collapse tests have been performed: i) tests of unsupported pipe and ii) test of pipes with external support from the cement and formation surrounding the pipe. While a paper from 2018 (OMAE2018-78767) considered casings without external support, the present paper pays attention towards supported pipes. Five collapse tests have been performed where test lengths of the 9 5/8” casing were installed inside a thick-walled pipe that simulates the support. A small gap leaves an annulus between the casing and the supporting pipe, allowing a controlled pressure to increase until collapse. The tests have been simulated by finite element analyses. Good correspondence was obtained, providing confidence that FE simulations can be used to predict the collapse capacity of supported pipes. While the tests were only performed for an idealized case with support around the whole circumference, a large number of FE simulations have been carried out for different combinations of support conditions together with variations in pipe ovality and internal wear from drilling. Ideally, the space between the casing and the rock formation is filled by cement. However, in practice there may be channels where there is no cement, likely to occur if the casing is eccentric in the well bore during cementing. These results from these FE simulations have been used to generate a response surface. Subsequent structural reliability analyses have been performed, in which well specific uncertainty associated with the above parameters is considered. Measurements and logging are used to minimize the uncertainty in these inputs and thereby leading to a reduction in the calculated failure probability. The probability of casing collapse is calculated conditional on different magnitude of the differential pressure of the pipe. By using SRA the potential over-conservatism in the conventional deterministic analysis is avoided. The SRA results were used to assist in the risk evaluation resulting in an allowance for continued production on existing wells.

Structural Reliability Analysis Using Fuzzy Finite Element Method

2013 ◽  
Vol 471 ◽  
pp. 306-312 ◽  
Author(s):  
A.Y.N. Yusmye ◽  
B.Y. Goh ◽  
A.K. Ariffin
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Reliability Analysis ◽  
Structural Reliability ◽  
Classical Method ◽  
Practical Method ◽  
Main Role ◽  
Structural Reliability Analysis ◽  
Fuzzy Finite Element ◽  
Element Method

The main requirement in designing a structure is to ensure the structure is reliable enough to withstand loading and the reliability study of structure. Classical and probability approach was introduced to analyse structural reliability. However, the approaches stated above are unable to take into account and counter the uncertainties arising from the natural of geometry, material properties and loading. This leads to the reduction in accuracy of the result. The goal of this study is to assess and determine the reliability of structures by taking into consideration of the epistemic uncertainties involved. Since it is crucial to develop an effective approach to model the epistemic uncertainties, the fuzzy set theory is proposed to deal with this problem. The fuzzy finite element method (FFEM) reliability analysis conducted has shown this method produces more conservative results compared to the deterministic and classical method espacially when dealing with problems which have uncertainties in input parameters. In conclusion, fuzzy reliability analysis is a more suitable and practical method when dealing with structural reliability with epistemic uncertainties in structural reliability analysis and FFEM plays a main role in determining the structural reliability in reality.

Wellhead Fatigue Analysis Method: Benefits of a Structural Reliability Analysis Approach

2012 ◽  
Author(s):  
Torfinn Hørte ◽  
Lorents Reinås ◽  
Jan Mathisen
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Offshore Structures ◽  
Probability Of Failure ◽  
Fatigue Analysis ◽  
Life Extension ◽  
Inspection Planning ◽  
Structural Reliability Analysis ◽  
Extreme Load ◽  
Input Parameters

Structural Reliability Analysis (SRA) methods have been applied to marine and offshore structures for decades. SRA has proven useful in life extension exercises and inspection planning of existing offshore structures. It is also a useful tool in code development, where the reliability level provided by the code is calibrated to a target failure probability obtained by SRA. This applies both to extreme load situations and also to a structural system under the influence of a time dependent degradation process such as fatigue. The current analysis methods suggested for service life estimation of subsea wells are deterministic, and these analyses are associated with high sensitivity to variations in input parameters. Thus sensitivity screening is often recommended for certain input parameters, and the worst case is then typically used as a basis for the analysis. The associated level of conservatism embedded in results from a deterministic analysis is not quantified, and it is therefore difficult to know and to justify if unnecessary conservatism can be removed from the calculations. By applying SRA to a wellhead fatigue analysis, the input parameters are accounted for with their associated uncertainty given by probability distributions. Analysis results can be generated by use of Monte-Carlo simulations or FORM/SORM (first/second order reliability methods), accounting for the full scatter of system relations and input variations. The level of conservatism can then be quantified and evaluated versus an acceptable probability of failure. This article presents results from a SRA of a fictitious but still realistic well model, including the main assumptions that were made, and discusses how SRA can be applied to a wellhead fatigue analysis. Global load analyses and local stress calculations were carried out prior to the SRA, and a response surface technique was used to interpolate on these results. This analysis has been limited to two hotspots located in each of the two main load bearing members of the wellhead system. The SRA provides a probability of failure estimate that may be used to give better decision support in the event of life extension of existing subsea wells. In addition, a relative uncertainty ranking of input variables provides insight into the problem and knowledge about where risk reducing efforts should be made to reduce the uncertainty. It should be noted that most attention has been given to the method development, and that more comprehensive analysis work and assessment of specific input is needed in a real case.

Probabilistic Fracture Mechanics Structural Reliability Analysis of Reeled Pipes

2006 ◽  
Author(s):  
Hugo A. Ernst ◽  
Ricardo Schifini ◽  
Richard E. Bravo ◽  
Diego N. Passarella ◽  
Federico Daguerre ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Reliability Analysis ◽  
Structural Reliability ◽  
Crack Size ◽  
Probability Of Failure ◽  
Statistical Distribution ◽  
Assessment Procedure ◽  
Statistical Distributions ◽  
Probabilistic Fracture Mechanics ◽  
Structural Reliability Analysis

Structural integrity analyses are used to guarantee the reliability of critical engineering components under certain conditions of interest. In general, the involved parameters have statistical distributions. Choosing a single set of values for the parameters of interest does not show the real statistical distribution of the output parameters. In particular, offshore pipes installation by reeling is a matter of concern due to the severe conditions of the process. Since it is necessary to guarantee the integrity of the pipes, a probabilistic fracture mechanics reliability analysis seems to be the most adequate approach. In this work, a probabilistic fracture mechanics assessment approach to perform the structural reliability analysis of tubes subjected to a reeling process was developed. This procedure takes into account the statistical distributions of the material properties and pipe geometry, using a fracture mechanics approach and the Monte Carlo method. Two-parameter Weibull distributions were used to model the variability of the input parameters. The assessment procedure was implemented as a self-contained executable program. The program outputs are: the statistical distribution of critical crack size, amount of crack extension, final crack size and the cumulative probability of failure for a given crack size. A particular case of interest was studied; a seamless tube - OD 323.9 × wt 14.3 mm, was analyzed. Tolerable defect size limits (defect depth vs. defect length curves) for different probability of failure levels were obtained. A sensitivity analysis was performed; the effect of material fracture toughness and misalignment was studied.

The application of Structural Reliability Analysis on hull girder ultimate strength of bulk carriers-a trial on Safety Level Approach

2015 ◽  
Author(s):  
Daokun Zhang ◽  
Wenyong Tang
Keyword(s):  
Reliability Analysis ◽  
Ultimate Strength ◽  
Structural Reliability ◽  
Safety Level ◽  
Hull Girder ◽  
Structural Rules ◽  
Structural Reliability Analysis ◽  
Trial Analysis ◽  
Bulk Carriers ◽  
Partial Safety Factors

The International Maritime Organization is developing the Goal Based Standard, in which the Safety Level Approach(SLA) is one of the two parallel ways forward focusing on deriving explicit and reasonable safety level. During the development of Safety Level Approach, the Structural Reliability Analysis(SRA) is recognized as one of the useful tools. The application of SRA on the calibration of partial safety factors for hull girder ultimate strength is so far a typical illustration, which could be very helpful for the application of Safety Level Approach on the structural Rules in the future. China Classification Society (CCS) carries out a trial analysis with co-operation of Shanghai Jiao Tong University.

Wellhead Fatigue: Benefits of Structural Reliability Analysis Applied to Groups of Wells

2019 ◽  
Author(s):  
Torfinn Hørte ◽  
Michael Macke ◽  
Andreas Buvarp Aardal ◽  
Lorents Reinås ◽  
Pål Bjønnes ◽  
...  
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
Cyclic Fatigue ◽  
Local Analysis ◽  
Structural Reliability Analysis ◽  
Well Design ◽  
Different Seasons ◽  
Single Well ◽  
Response Surface Technique ◽  
Global And Local

Abstract This paper outlines the methodology when performing structural reliability analysis (SRA) for wellhead fatigue of a complete field compared to individual wells. The field consist of several well and template systems from different suppliers. Further this paper will emphasize on added knowledge that can arise from the field vs. well analysis approach. Finally, some advice and guiding on necessary prerequisites for launching a field SRA will be shared. The methodology followed previous advices, with the added element that all wells were categorized depending on similarities in well design. Furthermore, a number of local finite element analyses for a specified systematic set of variations in input parameters have been performed by relevant equipment manufacturers to calculate the fatigue stress at critical hot spots (load-to-stress curves). Similar actions on loads had to be performed. A comprehensive set of global load analyses for each of the different rigs that have been operating on the field where needed to assess the cyclic fatigue loads from historical operations on each well. Finally, global and local analysis results were then gathered, and used as input to the SRA combined with a response surface technique. The additional effort for making the underlying global and local analyses covering all wells, and not only a single well, is limited for a given type of wellhead system. The field results now provide the operator with an improved basis for planning of future operations on the field, and enables optimization of the drilling plan and utilization of rigs throughout the varying environmental conditions for different seasons of the year and different operations, while managing the associated risk.

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