Scaling the impacts of pore-scale characteristics on unstable supercritical CO₂-water drainage using a complete capillary number

Journal Article · 01 July 2019 · International Journal of Greenhouse Gas Control

DOI: https://doi.org/10.1016/j.ijggc.2019.04.010 · OSTI ID:1567166

Chang, Chun ^[1]; Kneafsey, Timothy J. ^[2]; Zhou, Quanlin ^[2]; Oostrom, Mart ^[3]; Ju, Yang  ^[4]

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1. China Univ. of Mining & Technology, Beijing (China). State Key Laboratory of Coal Resources and Safe Mining; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Energy Geosciences Division
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Energy Geosciences Division
3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
4. China Univ. of Mining & Technology, Beijing (China). State Key Laboratory of Coal Resources and Safe Mining, and State Key Laboratory for Geomechanics and Deep Underground Engineering

Geological carbon storage in deep aquifers involves displacement of resident brine by supercritical CO₂ (scCO₂), which is an unstable drainage process caused by the invasion of less viscous scCO₂. The unstable drainage is greatly complicated by aquifer heterogeneity and anisotropy and regarded as one of the key factors accounting for the uncertainty in storage capacity estimates. The impacts of pore-scale characteristics on the unstable drainage remain poorly understood. In this study, scCO₂ drainage experiments were conducted at 40 °C and 9 MPa using a homogeneous elliptical micromodel with low or high anisotropy, a homogeneous/isotropic hexagonal micromodel, and a heterogeneous sandstone-analog micromodel. Each initially water-saturated micromodel was invaded by scCO₂ at different rates with logC_a (the capillary number) ranging from -7.6 to -4.4, and scCO₂/water images were obtained. The measured CO₂ saturations in these centimeter-scale micromodels vary considerably from 0.08 to 0.93 depending on the pore-scale characteristics and capillary number. It was also observed that scCO₂ drainage follows the classic flow-regime transition from capillary fingering through crossover to viscous fingering for either of the low-anisotropy elliptical and heterogeneous micromodels, but with disparate crossover zones. The crossover zones of scCO₂ saturation were then unified with the minimum scCO₂ saturation occurring at logC$$_a^*$$= -4.0 using the complete capillary number (C$$_a^*$$)that considers pore characteristics. For the hexagonal and the high-anisotropy elliptical micromodels, a monotonic increase in scCO₂ saturation with increasing C$$_a^*$$ (without crossover) was observed. It appears that the complete capillary number is more appropriate than the classic capillary number when characterizing flow regimes and CO₂ saturation in different pore networks.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22), Materials Sciences & Engineering Division (SC-22.2); USDOE
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1567166
• Alternate ID(s): OSTI ID: 1780449
• Journal Information: International Journal of Greenhouse Gas Control, Vol. 86, Issue C; ISSN 1750-5836
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English