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| Titel |
Brine-phase spiking during CO2 injection at the Ketzin site, Germany |
| VerfasserIn |
Martin Sauter, Julia Ghergut, Horst Behrens, Tobias Licha, Mich. Kühn |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047625
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| Zusammenfassung |
| Tracer tests are an indispensable tool for characterizing georeservoirs with a view at
geotechnical uses like nuclear waste disposal, CO2 storage, or geothermal energy
extraction. They provide the only means of determining the fluid residence time
(i. e., the size of the reservoir) under a given flow regime. Further, single-well
tracer push-pull (injection-withdrawal) tests provide the best method for quantifying
fluid-rock contact surface areas, which play an important role in water-rock interactions,
dissolution/precipitation, heat exchange, matrix diffusion and sorption processes, and thereby
also in CO2 trapping by various mechanisms.
Within the CO2 long-term injection experiment being conducted at
the Ketzin site in Germany since 2008, two liquid-phase organic tracers were introduced into
the reservoir brine prior to the beginning of CO2 injection; the spiked brine was separated
from the CO2 plume by a negligibly-sized liquid chaser slug. This kind of brine-phase
spiking is intended to quantify the passive displacement of reservoir brines by the
injected CO2. The very low values of brine-phase tracer concentrations sampled in
various depths at two observation holes (in 50Â m and 100Â m distance from the
injection hole), amounting to less than 10-7 of their values at the injection hole, are
consistent with the predictions of numerical (semi-analytical) simulations of tracer
breakthrough signals in a radially-symmetric, immiscible-flow approximation (which is
acceptable for early times of CO2 plume spreading). Values of brine-phase tracer mass
recovery cannot be estimated from this experiment, because brine flow rates cannot be
measured at observation holes under the passive downhole sampling conditions
provided by the Ketzin experiment setup. In contrast with that, the CO2 transport
experiment to be conducted at the Heletz site in Israel within the MUSTANG project
, under forced-gradient dipole conditions, will
ensure well-defined discharge values for both the liquid and the gas phase, thus also enabling
mass recovery estimates.
The time schedule and operational constraints of the Ketzin experiment did not
allow to conduct single-well push-pull tests prior to CO2 injection. However, after a
longer shut-in period following CO2 injection, it may become possible to perform
mixed-phase sampling at the former injection hole. Since the brine-phase tracer will largely
remain concentrated around this hole, (i) most of it being dissolved in the reservoir
brine, (ii) part of it having diffused into reservoir rock, maybe also sorbed onto rock
surfaces, (iii) part of it having dissolved into supercritical CO2 (as far as supercritical
conditions will have prevailed), and (iv) part of the latter having moved away from
the injection hole along with the CO2 plume, this kind of ’push-pull’ experiment
could provide interesting information about fluid-rock and brine-CO2 interface
areas.
Acknowledgements:
We are grateful to J. Erzinger and M. Zimmer, as well as M. Alawi, D. Morozova,
F. Möller, F. Schilling, M. Wandrey and H. Würdemann (GFZ Potsdam) for sustained help
with brine-phase samplings, and for general operational support. Field work at the Ketzin site
was jointly financed by the GFZ Potsdam and by the University of Göttingen. Tracer analyses
and modeling work were conducted within the EU Seventh Framework Programme
FP7Â /Â 2007-2013, under grant agreement no. 227286, as part of the MUSTANG Project. |
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