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| Titel |
Pulsed-Neutron-Gamma (PNG) saturation monitoring at the Ketzin pilot site considering displacement and evaporation/precipitation processes |
| VerfasserIn |
Gunther Baumann, Jan Henninges |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074585
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| Zusammenfassung |
| The storage of carbon dioxide (CO2) in saline aquifers is a promising option to reduce
emissions of greenhouse gases to the atmosphere and to mitigate global climate change.
During the proposed CO2 injection process, application of suitable techniques for
monitoring of the induced changes in the subsurface is required. Existing models for the
spreading of the CO2, as well as mixing of the different fluids associated with saturation
changes or resulting issues from mutual solubility between brine and CO2, need to be
checked.
For well logging in cased boreholes, which would be the standard situation encountered
under the given conditions, only a limited number of techniques like pulsed neutron-gamma
(PNG) logging are applicable.
The PNG technique uses controlled neutron bursts, which interact with the nuclei of
the surrounding borehole and formation. Due to the collision with these neutrons,
atoms from the surrounding environment emit gamma rays. The main PNG derived
parameter is the capture cross section (Σ) which is derived from the decline of
gamma rays with time from neutron capture processes. The high Σ contrast between
brine and CO2 results in a high sensitivity to evaluate saturation changes. This
makes PNG monitoring favourable for saturation profiling especially in time-lapse
mode.
Previously, the conventional PNG saturation model based on a displacement process has been
used for PNG interpretation in different CO2 storage projects in saline aquifers. But in
addition to the displacement process, the mutual solubility between brine and CO2 adds
further complex processes like evaporation and salt precipitation, which are not
considered in PNG saturation models. These evaporation and precipitation processes are
relevant in the vicinity of an injection well, where dry CO2 enters the reservoir.
The Σ brine value depends strongly on the brine salinity e.g. its chlorine content
which makes PNG measurements suitable for evaporation and salt precipitation
monitoring.
Within the framework of the EU project CO2CARE, funded by the European Commission
(FP7) and by industrial partners, an extended saturation model is developed. This extended
saturation model, including both the displacement and evaporation/precipitation process, is
applied to the PNG monitoring data of the injection well at the Ketzin pilot site. For the PNG
monitoring data of the observation wells the conventional saturation model based on the
displacement process is applied, because the arriving CO2 is already water saturated and no
water can be evaporated anymore. The methodological background of the extended saturation
model and results of the PNG saturation monitoring program at the Ketzin pilot site are
presented. |
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