Abstract
Geological storage of CO2 is the most promising technique to reduce the concentration of greenhouse gases in the atmosphere. In sedimentary basins at depths below 800 meters, CO2 can dissolve in the in-situ fluids, as well as to be stratigraphically trapped under the caprock, which needs to have high sealing capacity to prevent leakage. Shales are clay-rich fissile geomaterials that are widespread in the Earth’s subsurface and, giving their ductility and nanoscale pore size, they seem to be the ideal candidates for the sealing formations. The characterization of shale properties is challenging due to their high sensitivity to applied temperatures and pressures and nanoDarcy range permeabilities that imply weeks to months long time scales for saturation and flow processes. We developed laboratory techniques aimed at measuring one- and two-phase flow properties of the three types of shale specimens: intact, remolded, and naturally fractured. CO2 breakthrough pressure and flow properties appeared to be strongly dependent on the caprock microstructure and this relationship appears to be of a complex nature. While all three materials had the same mineralogy and approximately the same pore size distribution, the permeability was different by two orders of magnitude between fractured and intact specimens and by one order of magnitude between remolded and intact shale. Similarly, the CO2 breakthrough pressures appeared to be the lowest (around 2 MPa) for the fractured shale, while for the intact one it was above 10 MPa. Bonding between the grains and small discontinuities often times are not captured even by a micro-scale characterization techniques but appear to have a crucial influence on caprocks’ sealing capacity. Careful investigation of CO2 breakthrough and permeability into the caprock has to be conducted, considering various materials under representative in-situ temperatures and pressures.
Short bio
Roman Y. Makhnenko is an assistant professor in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign. Roman received his undergraduate degree in mechanics and applied mathematics at Lomonosov Moscow State University, Russia, in 2007. He then obtained his MS (2009) and PhD (2013) degrees in geological and civil engineering from the University of Minnesota – Twin Cities. From 2013 to 2016, Dr. Makhnenko worked as a postdoctoral researcher and lecturer at the Swiss Federal Institute of Technology in Lausanne (EPFL, Switzerland) on the project related to assessment of geological storage of CO2. Dr. Makhnenko’s research interests include development of laboratory methods and constitutive models for characterizing fluid-saturated geomaterials’ behavior under elevated temperatures and pressures with applications to deep CO2 storage, nuclear waste storage, and enhanced geothermal systems.
