Abstract
Small- and ultra-small angle neutron scattering (SANS and USANS) provide powerful tools for quantitative analysis of porous rocks, yielding bulk statistical information over a wide range of length scales. This study utilized (U)SANS to characterize shallowly buried quartz arenites from the St. Peter Sandstone. Backscattered electron imaging was also used to extend the data to larger scales. These samples contain significant volumes of large-scale porosity, modified by quartz overgrowths, and neutron scattering results show significant sub-micron porosity. While previous scattering data from sandstones suggest scattering is dominated by surface fractal behavior over many orders of magnitude, careful analysis of our data shows both fractal and pseudo-fractal behavior. The scattering curves are composed of subtle steps, modeled as polydispersed assemblages of pores with log-normal distributions. However, in some samples an additional surface-fractal overprint is present, while in others there is no such structure, and scattering can be explained by summation of non-fractal structures. Combined with our work on other rock-types, these data suggest that nanoporosity is more prevalent, and may play a much more important role than previously thought in fluid/rock interactions.
| Original language | English |
|---|---|
| Pages (from-to) | 280-305 |
| Number of pages | 26 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 102 |
| DOIs | |
| State | Published - Feb 1 2013 |
Funding
Effort by L.M.A., G.R. and L.F.A. was supported by research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy. D.R.C. was funded by the Department of Energy Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences through the Energy Frontier Research Center – Nanoscale Control of Geologic CO 2 . We acknowledge the support of the National Institute of Standards and Technology, Center for Neutron Research, U.S. Department of Commerce, and the High-Flux Isotope Reactor at the Oak Ridge National Laboratory in providing the research neutron facilities used in this work. This work utilized facilities supported in part by the National Science Foundation under agreement No. DMR-0944772. Certain commercial equipment, instruments, materials and software are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, the Department of Energy, or the Oak Ridge National Laboratory, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. John Valley, Mike Spicuzza, Anthony Pollington, and Brian Hess at the University of Wisconsin - Madison provided samples and aided in sample preparation as part of research sponsored by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy under contract 93ER14389 at the University of Wisconsin - Madison. Help and comments from Dr. Hsiu-Wen Wang were greatly appreciated. We would also like to thank Dr. Michael Schmid, Institut für Angewandte Physik, Technische Universität Wien, for his help with the ImageJ plugins for calculating the autocorrelation functions and scattering curves from the BSE images.
| Funders | Funder number |
|---|---|
| Department of Energy Office of Basic Energy Sciences | |
| National Institute of Standards and Technology, Center for Neutron Research | |
| University of Wisconsin - Madison | 93ER14389 |
| National Science Foundation | DMR-0944772 |
| U.S. Department of Energy | |
| U.S. Department of Commerce | |
| Basic Energy Sciences | |
| Oak Ridge National Laboratory | |
| Chemical Sciences, Geosciences, and Biosciences Division |