Ph.D. student: Gunnar Skúlason Kaldal
Dissertation title: Nonlinear Finite-Element Analysis of Casings in High-Temperature Geothermal Wells
Dr. Arve Bjørset, Principal Researcher Equinor Research Center, Professor II, Western Norway University of Applied Science.
Dr. Catalin Teodoriu, Associate Professor & Drilling Simulation Center Director of Mewbourne School of Petroleum and Geolocical Engineering, University of Oklahoma.
Advisor: Dr. Magnús Þór Jónsson, Profssor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science at the University of Iceland
Dr. Halldór Pálsson, Profssor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science at the University of Iceland
Dr. Sigrún Nanna Karlsdóttir, Profssor at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science at the University of Iceland
Chair of Ceremony: Dr. Rúnar Unnþórsson, Professor and the Head of the the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science at the University of Iceland.
High-temperature geothermal wells are drilled in stages and constructed of several concentric steel casings that are cemented over their entire external surface for sealing and structural support purposes. The structural integrity of such casings is essential during drilling and for safe operation after the construction phase. High pressures can in some cases cause casing failures but the most powerful mechanical force is driven by large temperature changes from an initially cooled to a hot operating well. Thermal expansion generates large stresses in the casings which are constrained by cement and therefore, in conventional hightemperature wells, permanent plastic strains are formed as the wells warm-up to production temperatures. Elevated temperatures cause material strength reduction, further increasing the risk of failures. Casing failures, e.g. collapse and axial tensile rupture, can occur during the lifetime of wells and it is important to analyze the load history of casings thoroughly to evaluate risks of such failures. With recent increasing interest in drilling deeper geothermal wells, for seeking higher enthalpy geothermal fluids, the strength of the casing becomes one of the limiting factors due to higher temperatures, pressures, and difficult corrosive conditions. The structural integrity of the casing of otherwise productive wells can determine if they are a success or not. Nonlinear material properties, large displacements and connections between multiple contacting surfaces form a structural system which in this thesis is analyzed numerically with the use of the nonlinear finite-element method (FEM). The resulting models provide tools that are used for structural analysis in support to failure analysis, well design and material selection. This thesis describes problems of casing failures and structural analysis that provide a platform for better understanding and improvements of casings in high-temperature geothermal wells.
About the doctoral candidate:
Gunnar received a B.Sc. degree in June 2007 and a M.S. degree in June 2009 both in Mechanical Engineering from the University of Iceland. After graduation he began his PhD studies at the University of Iceland. Part of his studies have been conducted at the Innovation Center in Iceland. Gunnar has been a part time teacher at University of Iceland and United Nations University Geothermal Training Programme and has been working full time as an engineer at ÍSOR - Iceland GeoSurvey since October 2015.
Gunnar Skúlason Kaldal