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Titel |
The LEMAM array for CO2 injection monitoring: modelling results and baseline at Ketzin in August 2008 |
VerfasserIn |
J.-F. Girard, B. Bourgeois, J. Rohmer, C. Schmidt-Hattenberger |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250025657
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Zusammenfassung |
Several teams have proposed to follow the variation of electrical resistivity at depth in order
to monitor the CO2 injection. This approach seems especially relevant in the case of CO2
injection in saline reservoir where the CO2 plume is expected to generate a strong increase of
the electrical resistivity.
Due to its greater density, supercritical CO2 occupies a much smaller volume and shows
reduced buoyancy as compared to gaseous CO2. The reservoir should thus be deep enough
for the CO2 to be in a supercritical state. Assuming a geothermal gradient of 25Ë C/km from
15Ë C at the surface, and a standard hydrostatic pressure, CO2 is supercritical at depth greater
than 800m. And many envisaged reservoirs are even much deeper. This makes it very difficult
to detect and monitor any change in the reservoir using electrical methods from the
surface. Logging and cross-well electrical or electromagnetic (EM) imaging overcome
this limitation but they need wells intersecting the reservoir and compatible for
such measurements. In addition, the lateral investigation is limited to the inter-well
area or to the close vicinity of the unique well in the case of logging or single-well
methods.
We propose to illuminate the deep CO2 plume by a grounded injection of electrical
current through the available metal-cased boreholes (CO2 injection or monitoring boreholes,
possibly pre-existing boreholes in the case of depleted hydrocarbon reservoir) which act as
long electrodes and to measure the resulting electric field at the surface. We designate this
array as Long Electrode Mise À La Masse (LEMAM). Considering industrial-scale CO2
injection rates (-Â 1Â Mt/y), the first numerical simulations performed within the
projects GeoCarbone-Monitoring and EMSAP-CO2 of the French Research Agency
(ANR) have shown that, even for a reservoir as deep as 2000Â m, when the volume
of the plume increases, the resulting electric field modification at the surface is
perfectly measurable. Furthermore, this array shows a good sensitivity to the plume
shape.
In the framework of the CO2ReMove EC project, a baseline with the LEMAM array has
been performed at the Ketzin site in August 2008, at the beginning of the CO2 injection.
Repetitions are planned in 2009 and later as a first field application of the LEMAM array to
CO2 storage monitoring. The surface electric field was recorded using several pairs of
perpendicular electrical dipoles (100Â m length) distributed in the area surrounding the CO2
injection borehole (approximately 1Â km around the borehole head). It will be interesting to
compare our results with the electrical resistivity monitoring performed in the framework of
the CO2SINK project, using either cross-borehole electrical resistivity tomography
(VERA experiment, Helmholtz Centre Potsdam/ GFZ) or surface injection coupled
with surface-downhole-measurements (in cooperation with University of Leipzig). |
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