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.

Tight carbonate rocks are important potential although unconventional geothermal and hydrocarbon underground storage reservoirs and prospective CO 2 -EGS sites. We study these rocks by using the Upper Jurassic “Malm ß” in Southern Germany as an outcrop analog example to understand bulk properties in relation to microstructure and to test a variety of models for permeability prediction. Bulk petrophysical methods (Archimedes isopropanol immersion method, Helium pycnometry, mercury injection capillary pressure, gamma density core logging, gas permeability measurements) combined with microstructural investigations (BIB-SEM) are applied. Samples are macroscopically undeformed limestones collected from a tectonically overprinted quarry wall near the town of Simmelsdorf (38 km NE of Nürnberg city). Bulk porosities are below 5% and argon permeabilities are on average 1.4E-17m 2 . The presence of stylolites in some of the samples has neither a significant effect on porosity nor permeability. Pore sizes are in the submicron range and the diagenetically lithified stiff limestones are characterized by a relatively high Young’s Modulus averaging 73±5 MPa. Moreover, no trends in properties were observable towards the faults, indicating 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 stratigraphic equivalent rocks of the South German Molasse Basin, illustrating the widespread homogeneity of these rocks and justifying the quarry scale (500 x 580 m) as a reasonable reservoir analog for these rocks in the subsurface. The application of various permeability prediction models showed that the Capillary Tube model and the Saki Model are very well suited for predicting permeabilities from BIB-SEM and mercury injection capillary pressure results, respectively. We thereby found that the matrix permeability is primarily controlled by the pore throat diameters rather than the effective porosity.