 |
| Titel |
New sensor approach for separating CO2 - sources in subsurface monitoring |
| VerfasserIn |
Detlef Lazik, Sebastian Ebert, Hans-Joerg Vogel |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053423
|
|
|
|
|
|
| Zusammenfassung |
| Carbon dioxide (CO2) is the most abundant gas in volcanic and post-volcanic regions. The
CO2 - discharges occur as plumes, fumaroles and mofettes but also as diffuse soil
emanations. Studies in volcanic or post-volcanic regions clearly demonstrated the risk of
significant CO2 fluxes from deep formations into the atmosphere with local concentrations up
to nearly pure CO2.
For greenhouse-gas mitigation it is planed to store billions of tons of CO2 in deep
geological formations (Carbon Capture & Storage - CCS) during the next decades. The CCS -
CO2 from such geological repositories can move along of permeable geological structures
forming local or even diffuse leakages at the surface.
For safety reasons, monitoring of such geological CO2 is required. Variable
meteorological patterns and the landscape morphology highly affect the atmospheric CO2
concentration close to the land surface. Thus, in terms of risk forecasting monitoring of
CO2 is more reliable below the soil surface where the concentration is much less
influenced by the atmospheric conditions. Ideally, measurements in soil should be able to
distinguish between the natural background concentration and the additional CO2 coming
from the geological source. This additional concentration might be comparable to
the concentration of the background CO2, which is produced by root respiration,
microbial respiration and oxidation of organic matter and varies in dependence of
temperature, moisture, soil type, cultivation, vegetation cover and herewith also with
temporal changes in the land use. Thus, the separation of theses different sources is
challenging.
Actually, the isotopic investigation of the soil CO2 or a detailed geochemical analysis of
the gas phase are applied for differentiation of both sources, however the effort is
considerable. We introduce a new approach which is expected to be more efficient and
economically more attractive. It is based on selective permeation of gases through a set of
two membranes. The tubular or point-like sensors can be installed in the soil. The
pressure evolution inside the individual sensor is related to the concentrations of
the different ambient gas species permeating the membrane. Our experiments and
theoretical considerations show that the time course of the differential pressure between
the two sensors is independent of the concentration but depends on the mixing
ratio between geological CO2 and background CO2. For a typical background of
pCO2 < 5% in soils we demonstrate a sufficient linearity of this dependency. In this
case, such mixing-line sensor can precisely operate in the field without excessive
calibration. |
|
|
|
|
|
|