Case Study Porosity Study of a Rock Sample with Avizo® Fire Abstract The purpose of this document is to describe different ways of studying a rock sample with Avizo® Fire software1. The rock sample studied comes from asphalt. Data was acquired with a Nanotom scanner (advanced 3D X-ray micro Computed Tomography scanner) from Phoenix X-ray, with courtesy of Delft University of Technology. Avizo® Fire software can be applied the multi-step workflow for porosity analysis of rock samples. From data loading to pores characterization, step-by-step methods can be applied, and further adjustments can be done to refine results. More generally, Avizo Fire enables 3D visualization and analysis of rocks, core samples, geomaterials, porous and other multi-phase materials at any scale, from any source (micro-CT, FIB/SEM, etc.), for statistical measurements, characterization or modeling. 1 This document includes previews of Avizo 6.2. However, the process described can also be achieved with Avizo 6.1 1. Data loading Loading the data into Avizo Fire is easy. The CT-scan data consists of a stack of 2D images that are read as a volume data set. Fast volume rendering gives the user a quick overall perspective of the data set, while instantaneous slice rendering provides a closer insight with accurate depiction of the porosity in the rock sample. 2. Filtering Three-dimensional image filtering is usually required before one can accurately segment. Our goal is to accurately delineate the pore space inside the rock, which is made up of low density values. It is critical to accurately preserve the boundaries between pores and rock because mislabeling on the boundary regions could lead to over- or underestimating the pore space. Looking at a portion of a slice, we notice that noise is present in both the pore space and the surrounding rock material. Before segmenting the pores, we can easily smooth out the noise without spoiling the pore-torock boundaries, by applying the edge-preserving smoothing filter in Avizo. This is a powerful smoothing filter that models the physical process of diffusion without smoothing the high gradient areas i.e. fast transitions between low and high densities. In order to quickly determine the appropriate parameters, we use the FilteredObliqueSlice module, which applies the filter to a single slice. This gives the user interactive response so he or she can adjust the parameters and review the results, and the user can change the slice to see the applied filter to other regions of the 3D volume. Once parameters are correctly set we apply the filter to the whole data set. 3. Porosity segmentation Avizo Fire offers an extensive set of tools for segmentation. We use a script-module Labeling/ SegWatershedOnGradient which enables fast and accurate pores and phases segmentation using advanced algorithms. A comprehensive description of this technique will soon be available in Avizo 6.2 under: Example 6: segmentation of rocks using watershed and gradient thresholding. As explained in the tutorial, we can’t just threshold pores, because some pore intensity values are “melted” in rocks. Combined with high gradients masking, the performed watershed algorithm provides fast and accurate porosity segmentation. In pore-rock boundary areas, the segmented pore boundary accurately indicates the physical location of the separation i.e. where gradient intensity is the highest. We now have a labeled volume and an associated porosity value. 4. First analysis By applying Avizo Fire’s interactive analysis tool to the segmented pore space, we instantaneously get pore volumes and characteristics. Avizo Fire can provide statistics, plot distribution and individual measures for the different regions, allowing the user to highlight, select and filter objects corresponding to measures. We notice that isolated pores are dispersed throughout the volume. As those pores have no effect on fluid flow, we can discard them and focus on the connected pore space. 5. Advanced connectivity analysis Our next goal is to try and define if pore connectivity is higher along an orientation through the rock sample. This information can give useful indications on the fluid flow behavior in the porous media by either giving the main fluid direction, or showing that there is no heterogeneity in porosity. By using the axis-connectivity module of Avizo 6.2, we can compute the pore connectivity along any of the three orthogonal axes. For this study case, axis-connectivity gives almost the same ratio along the X, Y or Z axis, suggesting that the rock sample has a homogeneous porosity. 6. Presentation and reporting Avizo helps you share, publish and present results, compute statistical reports, generate movies and make live demos of your research findings. 7. More tools for rock porosity study A number of additional tools are available to assist rock porosity analysis, such as morphometric parameters and propagation calculation. For accurate modeling of fluid behavior in rocks, users can apply computational tools of porosity and permeability which rely on extraction of geometric models determined by Avizo, such as the pore network skeleton or extraction of boundary surfaces and tetrahedral grids suitable for simulation. Avizo Fire is therefore the perfect platform for rock samples analysis and virtual experiment on rock behavior. It can easily integrate your existing tools, be adapted to your needs and fit in your specific workflow. Inertia moment ellipsoids About Avizo Avizo® software is a powerful, multifaceted tool for visualizing, manipulating, and understanding scientific and industrial data. Wherever three-dimensional data sets need to be processed, in materials science, geosciences, environmental science or engineering applications, Avizo offers abundant state-of-the-art features within an intuitive workflow and easy-to-use graphical user interface. www.avizo3d.com About VSG VSG brings more than 20 years of innovation to highly complex visualization challenges in the oil & gas, geosciences, materials science, engineering, and medical industries. We help our customers implement and benefit from ultimate visualization technologies through robust yet easy-touse tools and applications. We serve our world-class clients through offices in the United States, United Kingdom, France, Germany, and through distributors worldwide. Flow simulation results Propagation in a plug Skeletonization Image courtesy: IFP Contact us at [email protected] www.vsg3d.com Avizo is a registered trademark of VSG SAS. All other products mentioned may be trademarks or registered trademarks of their respective holders. VSG believes this information is accurate as of its publication date and is not responsible for any inadvertent errors. The information contained herein is subject to change without notice. © 2010 VSG, Visualization Sciences Group