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Prerequisites for density-driven instabilities and convective mixing under broad geological CO2 storage conditions
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Calif Berkeley, Lawrence Berkeley Natl Lab, Div Earth Sci, Berkeley, CA 94720 USA..
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
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2015 (English)In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 84, p. 136-151Article in journal (Refereed) Published
Abstract [en]

Direct atmospheric greenhouse gas emissions can be greatly reduced by CO2 sequestration in deep saline aquifers. One of the most secure and important mechanisms of CO2 trapping over large time scales is solubility trapping. In addition, the CO2 dissolution rate is greatly enhanced if density-driven convective mixing occurs. We present a systematic analysis of the prerequisites for density-driven instability and convective mixing over the broad temperature, pressure, salinity and permeability conditions that are found in geological CO2 storage. The onset of instability (Rayleigh-Darcy number, Ra), the onset time of instability and the steady convective flux are comprehensively calculated using a newly developed analysis tool that accounts for the thermodynamic and salinity dependence on solutally and thermally induced density change, viscosity, molecular and thermal diffusivity. Additionally, the relative influences of field characteristics are analysed through local and global sensitivity analyses. The results help to elucidate the trends of the Ra, onset time of instability and steady convective flux under field conditions. The impacts of storage depth and basin type (geothermal gradient) are also explored and the conditions that favour or hinder enhanced solubility trapping are identified. Contrary to previous studies, we conclude that the geothermal gradient has a non-negligible effect on density-driven instability and convective mixing when considering both direct and indirect thermal effects because cold basin conditions, for instance, render higher Ra compared to warm basin conditions. We also show that the largest Ra is obtained for conditions that correspond to relatively shallow depths, measuring approximately 800 m, indicating that CO2 storage at such depths favours the onset of density-driven instability and reduces onset times. However, shallow depths do not necessarily provide conditions that generate the largest steady convective fluxes; the salinity determines the storage depth at which the largest steady convective fluxes occur. Furthermore, we present a straight-forward and efficient procedure to estimate site-specific solutal Ra that accounts for thermodynamic and salinity dependence.

Place, publisher, year, edition, pages
2015. Vol. 84, p. 136-151
Keyword [en]
Carbon dioxide, CCS, Density-driven flow, Density instability, Double-diffusive convection, Porous media
National Category
Oceanography, Hydrology and Water Resources
Identifiers
URN: urn:nbn:se:uu:diva-265827DOI: 10.1016/j.advwatres.2015.08.009ISI: 000362305900012OAI: oai:DiVA.org:uu-265827DiVA, id: diva2:866619
Funder
Swedish Research Council
Available from: 2015-11-03 Created: 2015-11-03 Last updated: 2018-03-03Bibliographically approved
In thesis
1. Residual and Solubility trapping during Geological CO2 storage: Numerical and Experimental studies
Open this publication in new window or tab >>Residual and Solubility trapping during Geological CO2 storage: Numerical and Experimental studies
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Geological storage of carbon dioxide (CO2) in deep saline aquifers mitigates atmospheric release of greenhouse gases. To estimate storage capacity and evaluate storage safety, knowledge of the trapping mechanisms that retain CO2 within geological formations, and the factors affecting these is fundamental. The objective of this thesis is to study residual and solubility trapping mechanisms (the latter enhanced by density-driven convective mixing), specifically in regard to their dependency on aquifer characteristics, and to investigate and develop methods for quantification of CO2 trapping in the field. The work includes implementation of existing numerical simulators and inverse modeling, as well as the development of new models and experimental methods for the study and quantification of CO2 trapping.

A comparison of well-test designs in regard to their abilities to estimate the in-situ residual gas saturation (that determines the residual trapping of CO2) is presented, as well as a novel indicator-tracer approach to obtain residual gas saturation conditions in a formation. The results can aid in the planning of well-tests for estimation of trapping potential during site characterization.

Pore-network modeling simulations were conducted to study the effects of co-contaminant sulphur dioxide and formation thermodynamic and salinity conditions on residual CO2 trapping.

Furthermore, an analysis tool was developed and used to study the prerequisites for density-driven instability and convective mixing over broad geological storage conditions, including the relative influences of formation characteristics on factors controlling the convective process. The results show which conditions favour or disfavour residual and solubility trapping, knowledge useful for long-term predictions of the fate of injected CO2, and safety assessments during site selection.

An optical experimental method, the refractive-light-transmission (RLT) technique, and an analogue system design were developed for studying density-driven flow in porous media. The method exploits changes in light refraction to visualize convective flow, and incorporates a calibration procedure and an image post-processing scheme that enable quantification of solute concentration, density and viscosity within porous media. The experimental setup was used to study the dynamics of convective mixing, and to derive scaling laws for the onset time and mass flux of convection.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 81
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1640
Keyword
capillary trapping, CCS, convective flow, CO2, light transmission, SO2, well test
National Category
Earth and Related Environmental Sciences
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-343505 (URN)978-91-513-0257-7 (ISBN)
Public defence
2018-04-27, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2018-03-28 Created: 2018-03-03 Last updated: 2018-04-24

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Rasmusson, MariaFagerlund, FritjofTsang, YvonneRasmusson, KristinaNiemi, Auli

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