Recent Improvements in Subsea Wellhead Fatigue Monitoring Algorithm and Accuracy Using Verification and Calibration Techniques

Ge, Michael Long; Kebadze, Buba; Henderson, John M.; Zakeri, Arash

doi:10.4043/27613-ms

Cited by 4 publications

(2 citation statements)

References 6 publications

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“…One method that can be used for soil model verification is to compare the BOP stack natural frequency and the fixity point estimates obtained from measurements and predictive analysis (Ge et al 2017). The BOP natural frequencies are calculated from measurements using angular rates from riser and LMRP sensors.…”

Section: Soil Model Verification Methods Using Monitoring Datamentioning

confidence: 99%

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Soil Model Assessment for Subsea Wellhead Fatigue Using Monitoring Data

Mercan¹,

Chandra²,

Campbell³

et al. 2017

Day 1 Mon, May 01, 2017

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A significant effort is made by the industry through analyses and field monitoring to ensure delivery of safe and reliable wells. Fatigue analysis is an important aspect of well integrity assurance. Structural fatigue damage arises from stress changes caused by environmental cyclic loads acting on the riser system. In practice, the conductor-soil interaction under cyclic loading is modeled using the soil resistance-displacement (P-y) springs. Use of an appropriate soil model is essential for accurate determination of the fatigue damage. The American Petroleum Institute recommendations (API 2011) for P-y curves, which are often used for conductor-soil interaction analysis, have originally been developed for piled foundation and are inappropriate for well fatigue analysis. To that end, a new approach was developed by Zakeri et al. (2015) to derive P-y curves specifically for well fatigue analysis. Ultimate performance of each soil model can be determined and verified with field monitoring. This paper presents results of a field monitoring campaign for a well drilled in 354 ft water depth within a complex seabed stratigraphy comprising sands (loose to dense) and clays (very soft to stiff). Design, calibration and verification of the riser/conductor structural model using field data are presented in a companion paper (Ge et al. 2017). Herein, the effect of soil modeling on wellhead fatigue is discussed and predictions made with the API (2011) and the Zakeri et al. (2015) soil P-y springs are compared to field monitoring data. For the case presented herein, the results indicate that the Blowout Preventer (BOP) stack motion response is significantly affected by the soil stiffness and modeling methods. The predictions made with the Zakeri et al. (2015) model provided BOP response similar to those observed in the field both above and below the mudline. Whereas, the analyses done with the API (2011) model significantly overestimated the 'measured' conductor fatigue life above the mudline and underestimated it below. The results of this monitoring program are a step forward in better understanding system behavior of offshore wells.

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Section: Soil Model Verification Methods Using Monitoring Datamentioning

confidence: 99%

“…need to be considered in the analysis model calibration using field data. This is discussed in detail in a companion OTC 2017 paper (Ge et al 2017). BOP stack natural frequency and fixity point estimates are used as key parameters to calibrate analysis parameters based on field data.…”

Section: Introductionmentioning

confidence: 99%

Soil Model Assessment for Subsea Wellhead Fatigue Using Monitoring Data

Mercan¹,

Chandra²,

Campbell³

et al. 2017

Day 1 Mon, May 01, 2017

Self Cite

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Validation and Extension of Soil Response Framework for Fatigue Analysis of Offshore Wells and Piles

Zakeri

Sturm

Jeanjean

2019

Day 1 Mon, May 06, 2019

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A soil response framework for use in fatigue assessment of offshore wells and piles is presented. The framework covers clay and sand soil types. It was developed through comprehensive series of physical testing and numerical simulations. It hinges on determination of the unload-reload secant stiffness response of soils degraded under cyclic fatigue loading and reaching a steady-state condition. The framework comprises two calibrated approaches: spring-only and spring-dashpot. The latter is more appropriate when dynamic response of a structure needs to be more accurately determined through for time-domain analysis. Efficacy and validation of the framework are demonstrated through three (3) field monitoring programs involving offshore wells installed in ground conditions ranging from soft clays typically encountered in deepwater to layered sands and clays in shallow waters. Further validation is provided by presenting results from an extensive laboratory testing program involving nine (9) soil samples taken from various geographical locations against the key relationships of the framework. The laboratory tests were conducted in a novel apparatus developed specifically for obtaining soil resistance–displacement relationship for input to fatigue analysis.

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Overview of Joint Industry Project on Measurement Based Wellhead Fatigue

Mercan¹,

Chandra²,

Djayaputra³

et al. 2020

Day 2 Tue, May 05, 2020

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The objective of the wellhead fatigue joint industry project (JIP) is to provide a measurement-based foundation for drilling riser and wellhead modeling practice in the oil and gas industry and hence to ensure that the fatigue response assessment is performed with adequate but not overly conservative analysis parameters. To this end, the JIP utilizes field measurements from ten (10) drilling campaigns in GoM and North Sea. In order to maintain drilling campaign diversity, the field measurements are selected for a range of environments, water depths (110 to 1,900 m), soil characteristics, riser and wellhead configurations, and vessel types. The study commences with field data QA and filtration. Measurements are classified into wave-dominated events, VIV events and combined wave and VIV events. The finite element models of the as-built riser and wellhead systems are generated using industry standard analysis parameters, and simulations are conducted using measured motions near the top of the riser. The resulting numerical responses for the wellhead are compared with the measured motions to determine the level of conservatism (or otherwise) in the wave fatigue analysis. Additionally, SHEAR7 models driven by measured current profiles are used to compare predicted VIV fatigue response to that based on field measurements. Analysis results indicate that industry standard approach for wave and VIV fatigue assessment is indeed conservative. However, it should be noted that wellhead fatigue predictions through numerical simulations are affected by various analysis parameters, and it is impossible to determine the correct values for each of these parameters by using field measurements alone. In literature, several previous studies compared measured and predicted wellhead response. However, they often focus on a single drilling campaign, which makes it difficult to apply their findings to another drilling campaign. This JIP is the first in the industry to provide a combined assessment of full-scale field data from multiple drilling campaigns. Using consistent analysis techniques for all datasets offers valuable insight into riser and wellhead response characterization and safe drilling operations.

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Recent Improvements in Subsea Wellhead Fatigue Monitoring Algorithm and Accuracy Using Verification and Calibration Techniques

Cited by 4 publications

References 6 publications

Soil Model Assessment for Subsea Wellhead Fatigue Using Monitoring Data

Soil Model Assessment for Subsea Wellhead Fatigue Using Monitoring Data

Validation and Extension of Soil Response Framework for Fatigue Analysis of Offshore Wells and Piles

Overview of Joint Industry Project on Measurement Based Wellhead Fatigue

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