Joint interpretation of geoelectrical and soil‐gas measurements for monitoring CO₂ releases at a natural analogue

Abstract

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.

Improved time-lapse electrical resistivity tomography monitoring of dense non-aqueous phase liquids with surface-to-horizontal borehole arrays

“…ERT is well-established and widely employed in hydrogeological applications (e.g., Loke et al, 2013;Slater, 2007). Time-lapse ERT is a strongly emerging branch in applied geophysics (Supper et al, 2014), monitoring dynamic processes such as surface water-groundwater interaction (e.g., Slater et al, 2010), salt-water intrusion (e.g., de Franco et al, 2009), and CO 2 migration (e.g., Sauer et al, 2014). In the context of DNAPL site investigations, ERT exhibits significant potential due to the typically highly resistive nature of DNAPLs relative to groundwater (Lucius et al, 1992).…”

Microbial Signatures in Deep CO2-Saturated Miocene Sediments of the Active Hartoušov Mofette System (NW Czech Republic)

“…In addition, other deep biosphere habitats may exist that are associated with CO 2 reservoirs in geological trapping structures, as indicated by an increase in gas flow rates after swarm earthquakes pointing to a gas release after seismically induced fracking of sealing layers (Sandig et al, 2014 ; Sauer et al, 2014 ; Schuessler et al, 2016 ; Fischer et al, 2017 ). Additionally, Kämpf and Bankwitz ( 2005 ) described dm- to m-sized cavities in sediments of the nearby Nová Ves II open-cast mine at 50 mbs (meter below surface), which developed along fluid migration pathways.…”

Degassing Rhythms and Fluctuations of Geogenic Gases in A Red Wood-Ant Nest and in Soil in The Neuwied Basin (East Eifel Volcanic Field, Germany)

“…% in AA throughout the sampling (Table 1). Three different anomaly classes (after Sauer et al [42]; Table 2) were identified for CO 2 concentrations in the environments: (1) < 1 Vol. % (AA and NG), (2) 1–9.99 Vol.…”

“…Most of the SG concentrations are slightly elevated, but the very high levels in SG5 and SG1 indicate CO 2 anomalies (following [42]). Although higher ones have been reported (e.g., [9]), these are comparable to those recorded from the actively degassing Rapolano Fault [47] and therefore may be associated with an actively degassing but unknown fault on the Goloring site.…”

“… 1 Concentration classes according to [42]; 2 Atmospheric standard: 5.2204 ±0.0041ppm [18]; 3 Background concentration [43]; 4 Rn potential classes [44]. …”