Organic-rich shale samples from a lacustrine sedimentary sequence of the Newark Basin (New Jersey, USA) are investigated by combining Broad Ion Beam polishing with Scanning Electron Microscopy (BIB-SEM). We model permeability from this 2D data and compare our results with measured petrophysical properties. Three samples with total organic carbon (TOC) contents ranging from 0.7% to 2.9% and permeabilities ranging from 4 to 160 nD are selected. Pore space is imaged at high resolution (at 20,000x magnification) and segmented from representative BIB-SEM maps. Modeled permeabilities, derived using the capillary tube model (CTM) on segmented pores, range from 2.3 nD to 310 nD and are relatively close to measured intrinsic permeabilities. SEM-visible porosities range from 0.1% to 1.8% increasing with TOC, in agreement with our measurements. The CTM predicts permeability correctly within one order of magnitude. The results of this work demonstrate the potential of 2D BIB-SEM for calculating transport properties of heterogeneous shales.
Summary While the influence of clay smear on the sealing properties of fault zones in siliciclastic rocks can be predicted by validated concepts such as the SGR or CSP reliable models for predicting the structural and hydraulic properties of faults in layered limestone-marl sequences do not yet exist. The main goal of our study is to analyse the development of fault sealing as a result of marl smearing in interaction with mechanical mixing as well as fracturing and cementation processes in dependence of mechanically alternating bedding and fault geometry. Oriented transfer samples of fault cores from different normal fault systems destabilised by the fault process with adjacent damage zone were successfully extracted from outcrops with Jurassic limestone in a quarry Northern Bavaria, Germany. Microanalytical tools and multiscale (m-nm) analyses workflows were developed to provide ground truth for the training of machine learning algorithms for the efficient interpretation of 2D microstructural image data. The systematic macroscopic and microstructural examination of the transfer specimens has shown that the fault zones are built up by recurrent building blocks, whose variation and expression are strongly influenced by the presence and nature of interbedded marly layers.
<p>The main content of the Supplemental Material encompasses the data related to the thickness of deformation bands, particle diameter of host rock and deformation bands, host rock porosity, and the figure related to the 3D models.</p>
<p>The main content of the Supplemental Material encompasses the data related to the thickness of deformation bands, particle diameter of host rock and deformation bands, host rock porosity, and the figure related to the 3D models.</p>
Abstract Cataclastic bands in high-porosity sandstones significantly influence fluid flow, thus impacting the exploration and development of oil and gas. However, little experimental research has been conducted on the main factors controlling the formation, evolution, and physical properties of cataclastic bands. Moreover, it is difficult to use field surveys to discern variations and trends in the structural and physical properties of cataclastic bands formed during different deformation processes. In this study, we used a high-pressure and low-velocity ring-shear apparatus to analyze high-porosity, pure sandstone. Multiple sets of ring-shear experiments were carried out using the effective normal stress or shear displacement as a single variable. The experimental samples were analyzed based on physical property tests and thin sections. Our results indicate that the particles in the cataclastic bands generally have better roundness and are smaller (by at least two to three orders of magnitude) than the host rock. The porosity and permeability of the cataclastic bands are ~70% lower and two to three orders of magnitude lower than those of the host rock, respectively. The characteristics of the cataclastic bands are controlled by two main factors, namely, the effective normal stress and shear displacement. The effective normal stress controls the intensity of the cataclasis, and the shear displacement controls the physical properties of the grains and indirectly controls the evolutionary stage, which corresponds to the intensity of cataclasis. As the effective normal stress or shear displacement increases, the cataclasis in the cataclastic bands intensifies, and the grain size decreases; then, the decrease in the porosity gradually declines, and the permeability decrease and thickness increase and then plateau. The results of this study reveal the evolutionary mechanisms of the structural and physical properties of cataclastic bands in high-porosity sandstones and lay a theoretical foundation for determining the effect of these bands on fluid flow in oil and gas reservoirs.
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