Buckling Analysis of an Uncemented Tieback During Production, Injection and Pressure Tests

Benjamin Ulrich

Research output: ThesisMaster's Thesis

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Abstract

A MATLAB model is presented based on a detailed investigation of an uncemented tieback's behaviour and calculations in a vertical borehole of an Enhanced Geothermal System (EGS). It uses the input parameters and a given completion design as its basis for the calculations. An uncemented tieback is subject to load and buckling investigations under various operational modes. Results are presented in a user-friendly environment. The model considers all occurring axial loads, bending stresses, temperatures, internal and external pressures. Design factors need to be verified against axial, burst and collapse failure resistance in a biaxial design approach. Influenceable temperature distributions for the operational modes and temperature-dependent pressure calculations of the water inside the tieback simulate realistic conditions. An assessment is conducted on whether or not sinusoidal or helical buckling occurs under the provided user information. A visualisation of the numerical and graphical findings during production, injection and pressure test activities is implemented. The load cases are analysed against a base case without any operational loads. An EGS completion can be realised with a rigid design without freedom of movement or a vertically freely movable design. While the chance of buckling depends on the summation of all occurring forces, induced loads due to temperature changes and changes of the acting inside pressure are amongst the most influential ones. High compression can lead to the onset of buckling, either sinusoidal or helical. The buckling onset's determination is no exact science because of the various models presented in pieces of literature. Buckling can cause additional local bending stresses and contractions of the steel. Tensile and compressive loads have at the same time a mitigating but also deteriorating influence on the different failure criteria calculations. The findings suggest that simple buckling mitigation methods such as expansion devices could provide a sufficient remedy to extensive compressive loads. For completions that allow compensating loads with a change in length, negative axial loads can cause contraction while positive axial loads will lead to elongation. Thus, a freely moveable completion design shows benefits over a rigid design in regards to buckling. The easy to install and user-friendly model can provide a good first overview of an existing completion design under varying load cases without the necessity of expensive commercial software packages.
Translated title of the contributionBuckling-Analyse einer nicht zementierten Liner Rückverlängerung während der Produktion, Injektion und Druckprüfungen
Original languageEnglish
QualificationDipl.-Ing.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Fazeli Tehrani, Fatemeh, Co-Supervisor (internal)
  • Hofstätter, Herbert, Supervisor (internal)
Publication statusPublished - 2021

Bibliographical note

embargoed until null

Keywords

  • Buckling
  • Enhanced Geothermal System

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