A natural example of permeability reduction from porosity occlusion due to CO2 - rock interaction: implications for carbon capture and storage.
Abstract
To ensure the effective long-term storage of CO2 in potential geological storage sites, evaluation of leakage pathways and permeability changes due to fluid-rock interaction should be undertaken. Here we use a series of natural CO2 seeps along a fault in South Africa to assess the controls on CO2 leakage to the surface. Detailed mapping reveals extensive fracturing along the mapped fault trace. Measurements of gas flux and CO2 concentration, at sites along the fracture corridor, give 27% CO2 concentration (maximum soil gas measurements), and a flux of 191 g m-2 d-1. Flux and concentration measurements, with observations of gas bubbles in streams and travertine cones attest to CO2 migration to the surface. Permeability measurements on the host rock units show that tillite above the sandstone should act as an impermeable seal to upward CO2 migration to the surface. The combined permeability and fracture mapping data indicate that fracture permeability creates the likely pathway for CO2 migration through the low permeability tillite. Heterogeneity in fracture connectivity and intensity at a range of scales creates local higher permeability pathways along the fracture corridor. However, analysis of thin sections reveals that porosity occlusion occurs through time due to fluid-rock interaction decreasing fracture permeability. The results have implications for the assessment and choice of geological CO2 storage sites, particularly in the assessment of sub-seismic fracture networks and the interaction of CO2 fluid with rocks on permeability.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMMR53A0086B
- Keywords:
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- 1822 Geomechanics;
- HYDROLOGYDE: 1858 Rocks: chemical properties;
- HYDROLOGYDE: 5114 Permeability and porosity;
- PHYSICAL PROPERTIES OF ROCKSDE: 5139 Transport properties;
- PHYSICAL PROPERTIES OF ROCKS