3D microanalysis of geological samples with nanofocus computed tomography

Abstract

High resolution CT nowadays is a well established method for numerous industrial applications [Roth et al. 2003; Moller-Gunderson 2007; Nier et al. 2003] as well as for a wide range of research areas [Bonse 2004 and 2006]. During the last decade, Computed Tomography (CT) has progressed to higher resolution and faster reconstruction of the 3D-volume. Most recently it even allows a three-dimensional look into the inside of geological samples with submicron resolution. As shown by Brunke et al. [2008], nanoCT-systems in pursuit of high resolution images, the potential, convenience and economy can now compete in many application fields with high cost and rare available synchrotron facilities. Computed Tomography for geological purposes can lead to a new dimension of understanding of the distribution of rock properties. Especially spatial distribution of pores and pore-connections as well as cementation properties are of utmost importance in the evaluation of reservoir properties. Moreover rock analysis with the aid of X-ray Computed Tomography may lead to better analysis and prediction of well stimulation jobs. For example, a plug can be scanned before and after being stimulated with acid. The possibility to visualize the whole plug volume in a non-destructive way and to use the same plug for further analysis is undoubtedly currently the most valuable feature of this new type of rock analysis and will be a new area for routine application of X-ray Computed Tomography in the near future. The paper will outline the hard- and software requirements for high resolution CT. It will showcase several geological applications which were performed with the nanotom, the first 180 kV nanofocus CT system tailored specifically for highest-resolution scans of samples up to 120 mm in diameter and weighing up to 1 kg with exceptional voxel-resolutions down to <500 nm (<0.5 microns).