Petrophysical characterization, BIB-SEM imaging, and permeability models of tight carbonates from the Upper Jurassic (Malm ß), SE Germany

Geothermal Energy

Research

Norbert Klitzsch¹  Harald Stollhofen²  Wolfgang Bauer²  Simon Freitag²  Janos L. Urai³  Jop Klaver⁴  Joyce Schmatz⁴  Iulian S. Malai⁵ 

[1] Applied Geophysics and Geothermal Energy (E.ON Energy Research Center), RWTH Aachen University, Mathieustraße 10, 52074, Aachen, Germany;GeoZentrum Nordbayern, Friedrich-Alexander-Universität (FAU) Erlangen-Nürnberg, Schlossgarten 5, 91054, Erlangen, Germany;Structural Geology, Tectonics and Geomechanics, RWTH Aachen University, Lochnerstrasse 4-20, 52064, Aachen, Germany;GeoStructures Consultancy for Structural Geology and Geomechanics, Maastricht, The Netherlands;Structural Geology, Tectonics and Geomechanics, RWTH Aachen University, Lochnerstrasse 4-20, 52064, Aachen, Germany;MaP-Microstructure and Pores GmbH, Junkerstrasse 93, 52064, Aachen, Germany;Structural Geology, Tectonics and Geomechanics, RWTH Aachen University, Lochnerstrasse 4-20, 52064, Aachen, Germany;Shearwater GeoServices, 77 Mount Ephraim, Brockbourne House, Tunbridge Wells, TN4 8BS, Kent, UK;

关键词: Porosity;    Limestone;    Permeability;    Permeability models;    Malm;    Geomechanics;   

DOI  :  10.1186/s40517-022-00239-x

 received in 2022-05-30, accepted in 2022-11-16,  发布年份 2022

来源: Springer

【 摘 要 】

Tight carbonate rocks are important hydrocarbon and potential geothermal reservoirs, for example, in CO2-Enhanced Geothermal Systems. We report a study of outcrop samples of tectonically undeformed tight carbonates from the upper Jurassic “Malm ß” formation in Southern Germany near the town of Simmelsdorf (38 km NE of Nuremberg) to understand bulk petrophysical properties in relation to microstructure and to compare models for permeability prediction in these samples. We applied Archimedes isopropanol immersion, Helium pycnometry, mercury injection, gamma density core logging, and gas permeability measurements, combined with microstructural investigations and liquid metal injection (LMI-BIB-SEM). In addition, ultrasonic velocity was measured to allow geomechanical comparison of stratigraphically equivalent rocks in the South German Molasse Basin (SGMB). Results show only small variations, showing that the formation is rather homogeneous with bulk porosities below 5% and argon permeabilities around 1.4E−17 m2. The presence of stylolites in some of the samples has neither a significant effect on porosity nor permeability. Pores are of submicron size with pore throats around 10 nm and connected as shown by Mercury injection and Liquid Metal injection. Samples have high dynamic Young’s Modulus of 73 ± 5 GPa as expected for lithified and diagenetically overmature limestones. Moreover, no trends in properties were observable toward the faults at meter scale, suggesting that faulting was post-diagenetic and that the matrix permeabilities were too low for intensive post-diagenetic fluid–rock interaction. Petrophysical properties are very close to those measured in the SGMB, illustrating the widespread homogeneity of these rocks and justifying the quarry as a reasonable reservoir analog. Permeability prediction models, such as the percolation theory-based Katz-Thompson Model, Poiseuille-based models, like the Winland, the Dastidar, the capillary tube, and the Kozeny-Carman Models, as well as several empirical models, namely, the Bohnsack, the Saki, and the GPPT Models, were applied. It is shown that the capillary tube Model and the Saki Model are best suited for permeability predictions from BIB-SEM and mercury injection capillary pressure results, respectively, providing a method to estimate permeability in the subsurface from drill cuttings. Matrix permeability is primarily controlled by the pore (throat) diameters rather than by the effective porosity.

【 授权许可】

CC BY   
© The Author(s) 2022

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