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| Titel |
Preliminary investigation on the chemical response of cementitious grouts used for borehole sealing in geologically stored CO2 |
| VerfasserIn |
Konstantinos Giannoukos, Matthew Hall, Christopher Rochelle, Antoni Milodowski, Sean Rigby |
| 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 |
250090103
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| Publikation (Nr.) |
 EGU/EGU2014-4319.pdf |
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| Zusammenfassung |
| The successful geological storage of CO2 in underground reservoirs aims to immobilize
the injected CO2 stream in the form of secondary minerals through reaction with
primary minerals or pore fluids in the host rock formations. Injection wells and other
boreholes within the reservoir represent a major potential pathway for CO2 to leak back
to the surface. Therefore, the stability of well seals is a critical factor for the risk
assessment of existing and the design of new CO2 injection wells. Cement-based grouts
emplaced within the steel borehole liner, and between the liner and the rock formation,
must seal the well against leakage, both during the CO2 injection stage and for a
significant time after well abandonment, to allow for the CO2 to be immobilized though
rock-water interaction in the reservoir. The injected super-critical CO2 (scCO2)
experiences temperatures up to 180oC and pressures at depths greater than 800m, and
when dissolved in rock formation waters create chemically reactive species that
could impact the stability of cement seals. In an attempt to evaluate the impact of
scCO2-saturated fluids in class G oilfield grouts, batch experiments at 80bar and 60oC/
120oC were carried for pure cement and cement-steel cylindrical samples immersed
in a realistic formation porewater composition. Destructive and healing features
were observed by means of backscattered scanning electron microscopy (BSE) and
energy-dispersive X-ray microanalysis (EDS) elemental mapping; both phenomena
were evident in Ca leaching from, and deposition on, the surface of the samples,
respectively. Structural cement components like Si appear to have retained their original
particle-like shape in the regions affected by the CO2 in the 60oC experiments, but their
preservation at 120oC is vaguer. The liberation of Ca2+ from the hydrated cement
particles (indicated by local decrease of the Ca/Si ratio), and the reactions with the
incoming carbonate/bicarbonate anions seem to evolve progressively in distinct zones
formed parallel to the outer surface that are evident in BSE images. The proposed
mechanism of pH induced release of Ca2+ from C-S-H and Ca(OH)2 particles
due to CO2 fluids, and re-precipitation as carbonates seem to be controlled by the
fluid to solids ratio and as a result from the confinement of the exposed surface. |
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