Capillary heterogeneity trapping of CO2 in a sandstone rock at reservoir conditions

• Published in: Geophysical research letters Vol. 38; no. 15
• Main Authors: Krevor, Samuel C. M., Pini, Ronny, Li, Boxiao, Benson, Sally M.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-08-2011; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Capillarity; capillary; Carbon dioxide; CO2 sequestration; Earth sciences; Earth, ocean, space; Exact sciences and technology; Groundwater; Heterogeneity; High pressure; Hydrology; mutiphase flow; Permeability; Physical properties; Pore pressure; Power plants; Reservoirs; residual trapping; Rocks; Sandstone; Trapping; Upstream; experimental studies; steel; simulation; Carbon dioxide; permeability; reservoirs; storage; sandstone; saturation; drill cores; pore pressure; Planetary scale; temperature; clastic rocks; cross-bedding; geologic sections; inundations; technology; subsurface; high pressure; heterogeneity; capillarity; Mitigation; sedimentary rocks; sand; power plants; drainage
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2011GL048239

The storage of CO2 in deep subsurface porous rocks is being developed worldwide for the mitigation of emission from large industrial sources such as power plants and steel manufacturing. A main concern of this technology is in ensuring that the upwardly buoyant CO2 does not migrate to the surface. Simulation studies suggest that substantial amounts of CO2 can be trapped within permeable sections of a reservoir by capillary forces and intra‐reservoir heterogenities, but there is little experimental observation of these phenomena. We report the results of CO2 core flooding experiments at high pressure and temperature performed to investigate the impact of natural capillary heterogeneity in a sandstone rock on CO2 saturation buildup and trapping. CO2 and water were injected through a Mt. Simon sandstone core at 9 MPa pore pressure and 50°C. The core had two regions of distinct capillarity: An upstream 10 cm long region of the core consisted of a relatively high permeability and homogenous sand. A downstream 3 cm long region of the core consisted of a low permeability region characterized by significant cross‐bedding and a high capillary entry pressure for CO2. During a drainage process of CO2 displacing water, CO2 builds up upstream of the capillary barrier. Once in place, CO2 on the upstream side of the barrier cannot be displaced during 100% water flooding leading to trapped saturations that are a factor 2–5 times higher than what would be expected from residual trapping alone.
Key Points
Small capillary heterogeneity in sandstones lead to large CO2 saturation buildup
Saturation buildup is immobile even in the presence of a pressure gradient
Heterogeneity must be considered for accurate modeling of flow through sandstone