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| Titel |
Development of density plumes of dissolved CO2: Comparing experimental observations with numerical simulations |
| VerfasserIn |
Karen Kirk, Hayley Vosper, Chris Rochelle, Dave Noy, Andy Chadwick |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092082
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| Publikation (Nr.) |
 EGU/EGU2014-10001.pdf |
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| Zusammenfassung |
| The long-term trapping of CO2 within deep geological storage reservoirs will be dependent
upon CO2-water-rock geochemical reactions. The first, and most important, steps in this
process will be dissolution of CO2 into the reservoir porewater and the transport of this
dissolved CO2 through the reservoir. As part of the CO2CARE project we have investigated
these via laboratory tests using a water-filled porous medium. Key experimental
parameters were measured to determine system permeability, so that a high-resolution
numerical model could be built in an attempt to reproduce the observed system
behaviour.
The Hele-Shaw cell comprised two glass sheets 65 cm wide and 36 cm high, separated by a
spacing of 1.1 mm, and filled with closely-packed glass beads 0.4-0.6 mm in diameter. The
surface of the glass was treated to prevent the formation of a higher permeability zone along
this interface. A pH-sensitive dye was added to the pore-filling water to show where it had
been acidified due to the presence of CO2.
CO2 gas was introduced to a space at the top of the cell, which created a thin,
diffusion-controlled boundary layer of CO2-rich water below the CO2-water interface. CO2
dissolution increased water density, resulting in gravitational instabilities and the formation of
many small, downward-migrating plumes. Time-lapse photography was used to track the
formation and progress of these plumes. As the plumes grew they increased in length relative
to their width, and decreased in number over time. They also became more complex with
time, splitting and forming several lobes, whose outer edges became more diffuse as they
mixed with the CO2-poor water.
The onset time of plume development and the horizontal wavelength (spacing) of the
descending plumes are diagnostic measures of the system properties, notably permeability.
They were analysed from the time-lapse images and expressed as probability density
functions based on histograms of the observations. The derived permeability of
the system was calculated to be 2.2-2.5 x 10-9 m2, and this used for modelling
work.
Having experimentally reproduced the transition from diffusion-dissolution to
convection-dissolution, and from this determined the system properties, we simulated the
process in a numerical flow model. A high resolution model of the Hele-Shaw cell was built
using the TOUGH2 flow simulator with the ECO 2N fluid property module, with a
permeability of 2.5 x 10-9 m2, and applying laboratory pressure and temperature
conditions.
Plume development in terms of onset time, sinking rate and wavelength statistics are closely
comparable between experiment and model. This suggests therefore that the numerical flow
simulator was able to reproduce the critical process of transition from diffusion-dominated to
convection-dominated processes in a realistic way. This further increases our confidence in
the suitability of numerical models in making predictions of system evolution within CO2
storage schemes. |
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