Performance Evaluation of Recently Developed Soil Models in Well Conductor Fatigue Analysis using Field Measurements

Kannala, Jomon; Zakeri, Arash; Ge, Michael Long; Kebadze, Elizbar Buba

doi:10.4043/27186-ms

Cited by 7 publications

(3 citation statements)

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“…For calibration analysis, it was decided to use the Zakeri et al [2] model. This model has successfully been applied to predict stresses in two well monitoring campaigns in the North Sea [3] and in the Gulf of Mexico [4]. The upper bound soil properties are listed in Table 4.…”

Section: Figure 12 Fixity Point Estimates From Preliminary Analysis Mmentioning

confidence: 99%

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

Kebadze

Henderson

et al. 2017

Day 1 Mon, May 01, 2017

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Current subsea wellhead fatigue monitoring systems typically measure subsea BOP stack response and convert accelerations directly to the stress on various critical wellhead components using transfer functions. The veracity of this process relies on the accuracy of input data and the numerical modelling of the riser, subsea stack and wellhead conductor system. Poor representation of a real system could potentially yield an inaccurate calculation of transfer functions and consequently, imprecise estimation of the stress levels and predicted fatigue damage. The transfer function is strongly influenced by subsea stack system stiffness, which depends on dynamic soil response, stack hydrodynamic added mass and drag, location of the subsea stack fixity point, and stack-conductor system characteristic frequency. The latter two can be measured in the field and compared with predictions from numerical models. This paper evaluates the subsea wellhead fatigue monitoring algorithm and accuracy using verification and calibration techniques with field measurements. Important considerations for verification and calibration (e.g. soil property) are also discussed. The new approaches described are applicable to fatigue monitoring and analysis of subsea wellhead and conductor systems in both shallow and deep waters. The approaches presented herein could improve determination of the conductor fixity point and subsea stack characteristics, which in turn, would help in accurately determining wellhead fatigue and extracting displacements if needed. The good match between predicted and measured values of these parameters demonstrates that the numerical model and associated transfer functions are adequate for measured fatigue damage estimation. The transfer functions for fatigue monitoring systems and the associated subsea wellhead fatigue results could be significantly affected by the accuracy of the modelling methods and input data, particularly the soil properties. An inacccurate representation of the distance between the sensor and wellhead hot spot locations from which the transfer functions are derived could affect the accuracy of the fatigue results. For the case presented herein, the hydrodynamic properties drag loads and added mass have a less significant effect on the accuracy of transfer function and fatigue results.

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Section: Figure 12 Fixity Point Estimates From Preliminary Analysis Mmentioning

confidence: 99%

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

Kebadze

Henderson

et al. 2017

Day 1 Mon, May 01, 2017

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“…Russo et al (2016) compare measured deformations and stresses obtained from monitoring a well in the North Sea to those predicted using the p-y relationships recommended by API (2011) and Zakeri et al (2016a;2016b; and conclude that the latter approach yields predictions much closer to the measurements despite uncertainties in the site's soil properties. Kannala et al (2016) used the NC clay formulation from Zakeri et al (2015) with site specific soil information for a deepwater well in the…”

Section: Background Informationmentioning

confidence: 99%

Development of novel apparatus to obtain soil resistance–displacement relationship for well conductor fatigue analysis

et al. 2017

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An important aspect of deepwater well integrity is development of accurate conductor fatigue analysis due to cyclic loading during drilling operations. Fatigue damage in a structure occurs from stress changes in response to cyclic loading. In practice, the lateral cyclic soil response is typically modelled using Winkler p-y springs. However, recently developed soil models for conductor fatigue analysis were based on physical modelling in a geotechnical centrifuge.Notwithstanding the advantages of centrifuge modelling for investigating the conductor-soil interaction mechanism, development of simple laboratory tools to obtain p-y data directly from intact soil samples obtained from the field can also be very beneficial. This paper describes the development of a novel apparatus to obtain p-y and soil damping relationships from field samples specifically tailored for well conductor fatigue analysis. In addition, it compares the test results obtained using reconstituted kaolin clay and intact natural Onsøy clay to the centrifuge test results; ultimately demonstrating a satisfactory agreement between the two techniques.The results are highly encouraging and believe present a major step forward in deepwater well conductor fatigue analysis. The findings may also be beneficial to the offshore renewable energy sector.

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“…Few studies evaluating the Zakeri et al (2015) model based on field data have already been reported in literature (Kannala et al 2016, Myhre et al 2015, Lindstad et al 2015. While the method proposed performs very well in predicting the wellhead fatigue damage from the model test, the reliability of the new method needs to be verified using field data collected during a drilling campaign.…”

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

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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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Performance Evaluation of Recently Developed Soil Models in Well Conductor Fatigue Analysis using Field Measurements

Cited by 7 publications

References 1 publication

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

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

Development of novel apparatus to obtain soil resistance–displacement relationship for well conductor fatigue analysis

Soil Model Assessment for Subsea Wellhead Fatigue Using Monitoring Data

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