Wellhead Fatigue Damage Based on Indirect Measurements

Grytøyr, Guttorm; Coral, Fredy; Lindstad, Halvor Borgen; Russo, Massimiliano

doi:10.1115/omae2015-41379

Cited by 5 publications

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“…For further details on the theoretical background, see [6]. This is an advantage of the indirect method, since it can be used regardless of system configuration.…”

Section: Indirect Methodsmentioning

confidence: 99%

Direct And Indirect Measurement Of Well Head Bending Moments

2015

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During the past few years, there has been a focus on increased oil recovery, which has increased the demand for drilling operations on subsea wells. Furthermore, the BOPs have become significantly larger in size. As a consequence, well head fatigue has been a growing concern for offshore drilling in the North Sea.In order to assess accumulated fatigue damage on a wellhead system, it is necessary to have some knowledge of the load history. This can be established e.g. by use of global riser analyses. However, this will include some model uncertainty, and is known to be conservative in many cases. Improved confidence can be achieved by measuring the actual loads on the system, thus removing the uncertainty inherent in a numerical analysis. It is challenging to measure strains on a wellhead directly, however in some cases it is possible to measure the strains close to the Wellhead, thus allowing for direct measurements of the bending moments and axial forces. Statoil has been able to measure strains close to the WH on 3 different drilling MODUs. In one case this was accomplished by using strain gauges directly on a spool piece below the BOP stack, in a second case by measuring the strains on the conductor casing and the surface casing below the housings, and in a third case in the form of flange face gap variations on the BOP connector flange.The direct method uses strain gauges or displacement measuring pins to assess bending strains. These systems are valuable in a sense that they provide an accurate measure of the bending moments. However, in some situations it is not possible to measure these loads directly, e.g. due to space limitations, or when the BOP support structure complicates the load path in the stack. Furthermore, it is difficult to measure bending moments on the wellhead when the BOP has landed on a horizontal XT for completion. In these cases indirect methods must be utilized instead. This paper presents a method for indirect measurements of the bending moments on a wellhead.The indirect method uses inclinometers on the lower riser adapter and BOP stack and allows for calculation of the bending moments in any cross-section below the lower flex joint. The benefit is that this automatically corrects for the height difference between measuring stations and the well head datum. Previous work on this topic has focused on horizontal displacement on the BOP stack, see e.g. [5]. Our results indicate that BOP displacement is not a good indicator of well head moments. However, a high correlation is observed between BOP stack inclination and well head moments. Statoil is currently preparing papers concerning the theoretical background of these methods [6].Statoil is instrumenting and using both direct and indirect methods on several offshore drilling campaigns. Direct methods have been used to verify the indirect method, and the results show a good agreement. The results are used to monitor BOP stack behavior and well head fatigue, giving important input to the operational decision process.A measurement campaig...

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“…For further details on the theoretical background, see [6]. This is an advantage of the indirect method, since it can be used regardless of system configuration.…”

Section: Indirect Methodsmentioning

confidence: 99%

Direct And Indirect Measurement Of Well Head Bending Moments

2015

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“…During drilling operations, the wellhead system and top casings are designed to support dynamic loads from the connected riser via the blowout preventer (BOP) and/or lower marine riser package (LMRP) [1,2]. The wellhead is easily and inevitably 2 damaged due to a variety of factors, including the low-cycle and huge loads transmitted through the global riser system and the soil-casing weak interaction (especially in soft or very soft seabed soils) [4,5,6]. Currently, many studies are focusing on the hydrodynamic characteristics of floating units, as well as the static and dynamic behaviors, strength, and stability of riser joints [7,8,9,10,11].…”

Section: Introductionmentioning

confidence: 99%

“…The time-domain and frequency-domain techniques were often used to investigate fatigue damage to critical components of top-hole casings and at the wellhead [2,3]. Grytøyr et al [4] provided an indirect measurement-based technique for estimating bending moments at the wellhead. Li et al [6] studied the stability of a composite subsea wellhead, considering the effects of cement, waiting time, and riser joint end-resistance force.…”

Section: Introductionmentioning

confidence: 99%

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Untitled

2022

Brodogradnja

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Deepwater subsea wellheads may be significantly threatened under extreme sea conditions and operations, especially when the seabed is composed of very soft clay properties. A numerical model of a deepwater wellhead system is established using the classic ocean pipe element and nonlinear spring element of ANSYS to examine the behaviors of subsea wellheads in diverse seabed soil. Nonlinear spring elements coded in the APDL language are used to model three types of seabed soils: very soft soil, soft soil, and firm soil. The dynamic and quasi-static behaviors of the wellhead system in the typical coupled and decoupled models of the drilling riser system are particularly investigated in depth. The effects of the nonlinear seabed soil properties on the detailed wellhead are realistically simulated using time domain and extremum analysis. The results show that the softer the seabed soil, the greater the displacement, rotation angle, curvature, and bending moment of deepwater subsea wellheads. When the seabed soil reaches a particular depth, the mechanical characteristics of the wellheads under the three types of seabed soil conditions are almost simultaneously close to zero. Overall, several conclusions reached in this study may provide some useful references for design and stability analysis.

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Integrity Assessment of Offshore Subsea Wells: Evaluation of Wellhead Finite Element Model Against Monitoring Data Using Different Soil Models

Russo¹,

Zakeri²,

Kuzmichev

et al. 2016

Journal of Offshore Mechanics and Arctic Engineering

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Understanding well conductor–soil interaction mechanism plays an important role in well integrity assessment. Evaluation of field data obtained from monitored offshore wells can provide valuable insights into the matter. This paper presents a comparison of the numerical results obtained from a full three-dimensional (3D) finite element (FE) analyses model of the blowout preventer (BOP), wellhead (WH), conductor, and surface casing versus the field measured data obtained during drilling operations. Sensitivity studies were also performed for several parameters that were considered important in the local well response analysis under observed sea state conditions. The conductor–soil analyses were simulated using the Winkler spring p–y curves obtained by two different approaches: American Petroleum Institute (API) RP2GEO and a recently developed model by Zakeri et al. The results of bending moments in conductor and surface casing have indicated good agreement between FE model results and the field measurements.

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Wellhead Fatigue Damage Based on Indirect Measurements

Cited by 5 publications

References 0 publications

Direct And Indirect Measurement Of Well Head Bending Moments

Direct And Indirect Measurement Of Well Head Bending Moments

Untitled

Integrity Assessment of Offshore Subsea Wells: Evaluation of Wellhead Finite Element Model Against Monitoring Data Using Different Soil Models

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