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Title: Experimental Study of Porosity Changes in Shale Caprocks Exposed to CO2-Saturated Brines I: Evolution of Mineralogy, Pore Connectivity, Pore Size Distribution, and Surface Area

Carbon capture, utilization, and storage, one proposed method of reducing anthropogenic emissions of CO2, relies on low permeability formations, such as shales, above injection formations to prevent upward migration of the injected CO2. Porosity in caprocks evaluated for sealing capacity before injection can be altered by geochemical reactions induced by dissolution of injected CO2 into pore fluids, impacting long-term sealing capacity. Therefore, long-term performance of CO2 sequestration sites may be dependent on both initial distribution and connectivity of pores in caprocks, and on changes induced by geochemical reaction after injection of CO2, which are currently poorly understood. This paper presents results from an experimental study of changes to caprock porosity and pore network geometry in two caprock formations under conditions relevant to CO2 sequestration. Pore connectivity and total porosity increased in the Gothic Shale; while total porosity increased but pore connectivity decreased in the Marine Tuscaloosa. Gothic Shale is a carbonate mudstone that contains volumetrically more carbonate minerals than Marine Tuscaloosa. Carbonate minerals dissolved to a greater extent than silicate minerals in Gothic Shale under high CO2 conditions, leading to increased porosity at length scales <~200 nm that contributed to increased pore connectivity. In contrast, silicate minerals dissolved to amore » greater extent than carbonate minerals in Marine Tuscaloosa leading to increased porosity at all length scales, and specifically an increase in the number of pores >~1 μm. Mineral reactions also contributed to a decrease in pore connectivity, possibly as a result of precipitation in pore throats or hydration of the high percentage of clays. Finally, this study highlights the role that mineralogy of the caprock can play in geochemical response to CO2 injection and resulting changes in sealing capacity in long-term CO2 storage projects.« less
 [1] ;  [1] ;  [2] ;  [2] ;  [3] ;  [4] ;  [5] ;  [3] ;  [6] ;  [7]
  1. Colorado School of Mines, Golden, CO (United States). Hydrologic Sciences and Engineering Program
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
  3. Univ. of Wyoming, Laramie, WY (United States). Dept. of Geology and Geophysics
  4. Univ. of Wyoming, Laramie, WY (United States). Dept. of Geology and Geophysics. School of Energy Resources
  5. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  6. Univ. of Wyoming, Laramie, WY (United States). Chemical Engineering Dept.
  7. Colorado School of Mines, Golden, CO (United States). Civil and Environmental Engineering
Publication Date:
Grant/Contract Number:
AC05-00OR22725; FE0000730; R834387
Accepted Manuscript
Journal Name:
Environmental Engineering Science
Additional Journal Information:
Journal Name: Environmental Engineering Science; Journal ID: ISSN 1092-8758
Mary Ann Liebert, Inc.
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Flux Isotope Reactor (HFIR); Colorado School of Mines, Golden, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USEPA
Contributing Orgs:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Univ. of Wyoming, Laramie, WY (United States)
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; caprock; carbon sequestration; Gothic Shale; high temperature and pressure experiments; Marine Tuscaloosa; nitrogen gas adsorption; porosity; scanning electron microscope; small angle neutron scattering (SANS)
OSTI Identifier: