Thermal Effects on Subsea-Wellhead Fatigue During Workover Operations

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Intervention and workover operations can significantly affect the structural integrity of subsea-wellhead systems with regard to their fatigue life. The increasing frequency of these operations has called for a renewed focus on the fatigue capacity of subsea wells, which has greatly improved the overall methodology used for wellhead-fatigue analysis. However, thermal effects along the well have yet to be incorporated. This paper analyzes wellhead-fatigue damage during a workover operation considering the thermal effects.

Methodology

The goal of the present study is to investigate the effects of the temperature variation along the well on wellhead-­fatigue-damage rates by incorporating the temperature profiles of casing strings and cement into the fatigue-damage assessment of a particular wellhead system during a workover operation.

In this study, a decoupled approach is proposed. The temperatures of riser, wellhead, and well components are calculated for different instants during the workover operation using a finite-­difference method. Then, the temperature profiles for a given moment during the operation are incorporated into a 3D finite-element model (FEM) of the wellhead system.

A structural analysis with focus on stresses at the fatigue hot spots is performed. Subsequently, a dynamic analy­sis of the riser provides the loading time history to which the wellhead is subjected; finally, combining the results of the structural analysis and the riser-­response analysis enables the fatigue damage during the simulated operation to be estimated.

The well adopted in this study follows a conventional subsea-completion program on the Norwegian continental shelf, with four casing strings and a production liner.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 180065, “Thermal Effects on Subsea Wellhead Fatigue During Workover Operations,” by L. Cantinelli Sevillano, J. De Andrade, S. Sangesland, and M. Stanko, Norwegian University of Science and Technology, prepared for the 2016 SPE Bergen One Day Seminar, Bergen, Norway, 20 April. The paper has not been peer reviewed.
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Thermal Effects on Subsea-Wellhead Fatigue During Workover Operations

20 July 2016

Volume: 68 | Issue: 8

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