Design of an Annular Pressure Relief System for Geothermal Wells

Matthias Sturm

Research output: ThesisMaster's Thesis

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In a geothermal well, annular pressure is generated during production, when trapped annular fluids are heated up between casing strings. Due to the encapsulated fluid, an expansion of the fluid is not possible and thus, the pressure increases. This phenomenon is known as Annular Pressure Build up (APB) or Trapped Annular Pressure (TAP). It has been identified, that APB is an important cause, when casing collapse occurs. The fluid trapped in the annulus can cause a deformation of either the inner or the outer casing string, which can lead to a loss of the integrity of the well. This thesis is a conceptual study of downhole tools, which act against APB. The tool, named Annular Pressure Relieve System (APRS), should be fixed on the casing string and therefore, prevents the well from getting damaged by APB. Due to the small amount of available space between the casing strings, an important point of the tool is to find the balance between a small constructed space and a high-volume capacity. Further the high pressure and temperature conditions are a big challenge for the tool design. Another challenge is that the tool must be customized for different well designs (varying pressure and temperature conditions). Therefore, a mounting concept is designed to be able to adapt the APRS to different diameters. Furthermore, the mounting concept ensures that the tool can be installed without damaging the well or hindering the cement job. The thesis deals with the development of different concepts and describes the functional operation and technical details of them. Moreover, all concepts are evaluated and compared to each other. The upsides and downsides of the tool concepts are compared to existing methods. The thesis includes an overview of the current, available methods how to handle or avoid APB and the necessity of developing a new method (tool) is demonstrated. The thesis describes the necessary calculation steps to define the boundary conditions for the design of the tool. A graph is presented, which can be used to estimate the needed volume to compensate the pressure increase by knowing the pressure and temperature conditions. Finally, the two most suitable concepts are discussed and an outlook for the detailed design process is given.
Translated title of the contributionEntwicklung eines Ringraumdruckausgleichssystems für geothermische Tiefenbohrungen
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Eisner, Patrick, Co-Supervisor (internal)
  • Hofstätter, Herbert, Supervisor (internal)
  • Lentsch, David, Supervisor (external)
Award date28 Jun 2019
Publication statusPublished - 2019

Bibliographical note

embargoed until 20-05-2024


  • APB
  • TAP
  • annular pressure build up
  • trapped annular pressure

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