Synchrotron-based X-ray tomographic microscopy for rock physics investigations Claudio Madonna 1 , Beatriz Quintal 1 , Marcel Frehner 1 , Bjarne S. G. Almqvist 1 , Nicola Tisato 1 , Mattia Pistone 1 , Federica Marone 2 , and Erik H. Saenger 1 ABSTRACT Synchrotron radiation X-ray tomographic microscopy is a nondestructive method providing ultra-high-resolution 3D digital images of rock microstructures. We describe this method and, to demonstrate its wide applicability, we present 3D images of very different rock types: Berea sandstone, Fontainebleau sandstone, dolomite, calcitic dolo- mite, and three-phase magmatic glasses. For some samples, full and partial saturation scenarios are considered using oil, water, and air. The rock images precisely reveal the 3D rock microstructure, the pore space morphology, and the inter- faces between fluids saturating the same pore. We provide the raw image data sets as online supplementary material, along with laboratory data describing the rock properties. By making these data sets available to other research groups, we aim to stimulate work based on digital rock images of high quality and high resolution. We also discuss and sug- gest possible applications and research directions that can be pursued on the basis of our data. INTRODUCTION Three-dimensional information of rock microstructures is impor- tant for better understanding physical phenomena taking place at that scale (e.g., Sakellariou et al., 2007; Degruyter et al., 2010; Bai et al., 2011; Saenger et al., 2011; Pistone et al., 2012) and for rock characterization (e.g., Arns et al., 2001a; Dvorkin et al., 2008; Knackstedt et al., 2009; Madonna et al., 2012). Various meth- ods for obtaining a 3D image of the rock microstructure exist. They can be separated into two major groups: destructive and nondestruc- tive methods. If possible, the latter is preferable because the same rock sample can be used for further investigations after imaging, for example in laboratory testing. This allows a direct comparison between laboratory tests and calculations based on a digital rock image. The most common nondestructive 3D imaging method for earth sciences is X-ray computed tomography (CT). Figure 1 compares different resolutions and possible sample sizes for differ- ent types of X-ray CT methods. There is a clear trade-off between sample size and resolution. For each single material sample, the question has to be clarified if the chosen sample size is representa- tive for the given task to be considered. In the last decade, the X-ray microcomputed tomography (micro-CT) method became widely available and many modern studies have made use of it to obtain 3D rock images. The resolution of micro-CT (Figure 1) is high en- ough to image the spatial distribution of grains, pores, and pore fluids. The resulting 3D digital rock images are often used in nu- merical models to simulate various physical processes on the pore- scale. We give here two examples: First, Zhu et al. (2007) developed a digital-image-based simulation methodology, which is applied to evaluate the influence of heterogeneities in the porosity distribution on the evolution of tracer concentrations in imaged tracer tests. Sec- ond, Saenger et al. (2011) used a 3D rock image to numerically simulate the signature of a theoretically predicted slow S-wave, which is an effect of a viscous pore fluid. Additionally, 3D rock images can be used for predicting proper- ties such as porosity, permeability, pore size distribution, effective elastic moduli, and electrical conductivity. For example, permeabil- ity can be successfully predicted by numerically simulating fluid flow through 3D rock models, with the numerical results being in reasonable agreement with laboratory measurements (Arns et al., 2004; Fredrich, et al., 2006; Dvorkin et al., 2008; Degruyter et al., 2010; Narváez et al., 2010). In this case, the resolution of the micro- CT technique is sufficient because fluid pathways predominantly follow larger pores. However, if the porosity is much smaller than 1 μm (e.g., shale) the agreement might be less satisfactory because Manuscript received by the Editor 30 March 2012; revised manuscript received 17 August 2012; published online 18 January 2013. 1 ETH Zurich, Department of Earth Sciences, Zurich, Switzerland. E-mail: claudio.madonna@erdw.ethz.ch; beatriz.quintal@erdw.ethz.ch; marcel.frehner@ erdw.ethz.ch; bjarne.almqvist@erdw.ethz.ch; nicola.tisato@erdw.ethz.ch; mattia.pistone@erdw.ethz.ch; erik.saenger@erdw.ethz.ch. 2 Paul Scherrer Institute, Swiss Light Source, Villigen, Switzerland. E-mail: federica.marone@psi.ch. © 2013 Society of Exploration Geophysicists. All rights reserved. D53 GEOPHYSICS, VOL. 78, NO. 1 (JANUARY-FEBRUARY 2013); P. D53–D64, 15 FIGS., 2 TABLES. 10.1190/GEO2012-0113.1 Downloaded 02/05/13 to 137.222.114.247. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/