Fluid Flow Simulations of a Large-Scale Borehole Leakage Experiment
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Fluid Flow Simulations of a Large‑Scale Borehole Leakage Experiment Tim Klose1,2 · M. Carme Chaparro3 · Frank Schilling1 · Christoph Butscher4 · Steffen Klumbach1 · Philipp Blum1 Received: 28 November 2019 / Accepted: 28 October 2020 © The Author(s) 2020
Abstract Borehole leakage is a common and complex issue. Understanding the fluid flow characteristics of a cemented area inside a borehole is crucial to monitor and quantify the wellbore integrity as well as to find solutions to minimise existing leakages. In order to improve our understanding of the flow behaviour of cemented boreholes, we investigated experimental data of a large-scale borehole leakage tests by means of numerical modelling using three different conceptual models. The experiment was performed with an autoclave system consisting of two vessels bridged by a cement-filled casing. After a partial bleed-off at the well-head, a sustained casing pressure was observed due to fluid flow through the cement– steel composite. The aim of our simulations is to investigate and quantify the permeability of the cement–steel composite. From our model results, we conclude that the flow occurred along a preferential flow path at the cement–steel interface. Thus, the inner part of the cement core was impermeable during the duration of the experiment. The preferential flow path can be described as a highly permeable and highly porous area with an aperture of about 5 μm and a permeability of 3 ⋅ 10−12 m2 (3 Darcy). It follows that the fluid flow characteristics of a cemented area inside a borehole cannot be described using one permeability value for the entire cement–steel composite. Furthermore, it can be concluded that the quality of the cement and the filling process regarding the cement–steel interface is crucial to minimize possible well leakages. Keywords Borehole leakage · Sustained casing pressure · Permeability test · Cement · Modelling
* Tim Klose tim.klose@uni‑potsdam.de 1
Institute of Applied Geosciences (AGW), Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany
2
Present Address: Institute of Geosciences, University of Potsdam, Karl‑Liebknecht‑Str. 24‑25, Potsdam‑Golm 14476, Germany
3
Institute for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology (KIT), Hermann‑von‑Helmholtz‑Platz 1, 76344 Eggenstein‑Leopoldshafen, Germany
4
Geotechnical Institute, TU Bergakademie Freiberg, Gustav‑Zeuner‑Str. 1, 09599 Freiberg, Germany
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List of symbols A𝛼 Area of flow (m2) b Inner circumference casing (m) C Compressibility fluid (Pa−1) d Inner diameter casing (m) dL Length of element (m) F𝛼 Model specific factor (m4 Pa) h𝛼 Gap/area width (m) K Geometry factor for the ‘Hagen–Poiseuille’ model (–) k𝛼 Intrinsic permeability (m2) L Length over the pressure gradient (m) LC Length casing (m) N Number of cells (–) Pn Pressure at nth node(Pa) PBV Pressure bottom vessel (Pa) Patm Pressure atmosphere (Pa) Pinitialn Initial pressure values corresponding to
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