Evaluation of Micro-Fractures and Pore Plugging Effects in Caprock Shale

Research output: ThesisMaster's Thesis

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Wellbore instability problems are frequently encountered in drilling operations. Large cavings, which are recovered on the shale shakers, are the most prominent indicators and often give an abundance of information. For instance, the evaluation of the micro-fractures and the interaction between the drilling fluid and the shale itself, which are key factors to draw a better conclusion of the possible cause and prescribe solutions to prevent such problems in the future. By analyzing the samples of cavings obtained from a caprock shale of an oil field in Mexico, this master thesis aims to propose a methodology to better understand the root cause of the wellbore instability problems in this type of formations. The wellbore instability problem presented in the Mexican onshore wells included in this master thesis is associated with micro-fractured shale, anisotropic failure and weak bedding planes. This is evident by the appearance of three to four centimetres tabular cavings which causes a main problem when controlling the well and handling the cavings on the surface. This study covers in an integrated manner, real-time monitoring data analysis, geomechanical analysis, micro-CT scanning, shale characterization as well as an experimental set up of the HPHT (High Pressure High Temperature) filter press use for permeability plugging tests. The proposed setup of the HPHT filter press is designed to analyze the pore plugging effects in shale as well as the interaction between the drilling fluid and the actual rock. This is achieved by developing a replacement of the conventional ceramic disk with the shale samples obtained from the cavings. A methodology to prepare disk for the permeability plugging test from shale cavings was developed and is presented. The results of the laboratory tests, the geomechanical analysis and the shale characterization give us a better understanding of the behaviour of the shale under borehole conditions, the in-situ stress state of the area and the possible causes of the problem. The methodology applied in this thesis can be beneficial to optimize the selection of the LCM (lost circulation material) by analyzing the micro-fracture width in relation with the pore plugging effects.
Translated title of the contributionUntersuchung von Mikro-Frakturen und Porenschließungseffekten in dichten Tongesteinen
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Finkbeiner, Thomas, Supervisor (external)
  • Thonhauser, Gerhard, Supervisor (internal)
  • Ravi, Krishna, Co-Supervisor (internal)
  • Liebenberger, Marc-Philipp, Co-Supervisor (external)
Award date28 Jun 2019
Publication statusPublished - 2019

Bibliographical note

no embargo


  • wellbore instability
  • shale
  • cavings
  • micro-fractured shale
  • anisotropic failure
  • tabular cavings
  • permeability plugging test
  • HPHT filter press

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