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Joint interpretation of geoelectrical and soil‐gas measurements for monitoring CO 2 releases at a natural analogue
Author(s) -
Sauer U.,
Watanabe N.,
Singh A.,
Dietrich P.,
Kolditz O.,
Schütze C.
Publication year - 2014
Publication title -
near surface geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.639
H-Index - 39
eISSN - 1873-0604
pISSN - 1569-4445
DOI - 10.3997/1873-0604.2013052
Subject(s) - soil gas , electrical resistivity tomography , geology , environmental geology , regional geology , hydrogeology , groundwater , carbon capture and storage (timeline) , soil science , hydrology (agriculture) , environmental science , soil water , climate change , electrical resistivity and conductivity , geotechnical engineering , engineering , metamorphic petrology , telmatology , electrical engineering , oceanography
The development and validation of hierarchic monitoring concepts is essential for detecting and assessing possible leakages from storage formations, especially for carbon capture and storage (CCS) applications. Joint interpretation of various techniques (such as carbon dioxide (CO 2 ) concentration and flux measurements, self‐potential (SP) and geoelectrical surveys) showed that the combination of geophysical methods with soil‐gas analysis for mesoscale monitoring of the shallow subsurface above geologic CO 2 storages can be a valuable tool for mapping and monitoring potential CO 2 spread in the subsurface. Three measurement campaigns were undertaken – May 2011, July 2011 and April 2012 – at an analogue site in the Cheb Basin, Czech Republic, with the aim of studying CO 2 leakages and their temporal and spatial behaviour. Results of geoelectrical investigations give an insight into the structural features of the subsurface. CO 2 discharge into the atmosphere is mostly impeded by shallow, clay‐rich, partly water‐saturated zones, which can be seen in the electrical resistivity tomography (ERT) results. Several transport processes can be identified based on SP measurements. The SP results highlight the complex behaviour of temporal variations for the flow patterns. In particular, coupled migration of gas and water plays an important influencing role in this process. Site‐specific, near surface geological features and meteorological conditions seem to exert great influence on the degassing pattern and measured CO 2 values. Therefore, soil‐gas measurements represent a snapshot which illustrates both a distinct typical pattern of the soil‐gas distribution in the near subsurface and certain differences caused by soil and meteorological conditions. Observed CO 2 soil‐gas anomalies and modelled results suggest that the occurrence of gas discharge is much more localized around restricted areas, often controlled by local permeability contrasts. Hence, our results show that a proposed monitoring concept should integrate SP, time‐lapse ERT, meteorological parameters and soil‐gas measurements to provide a comprehensive insight into the subsurface structures and processes.