First geoelectrical image of the subsurface of the Hontomín site (Spain) for CO2 geological storage: A magnetotelluric 2D characterization

Magnetotelluric (MT) data provided a two-dimensional (2-D) resistivity model of the subsurface of the Technology Demonstration Plant (TDP) located in Hontomín (Burgos, Spain) for geological storage of CO2 in a deep saline aquifer. A first north–south profile of 22 broadband MT soundings was acquired to study the viability of the method to characterize the TDP subsurface. Stations were deployed at approximately 200-m intervals and the data were recorded in the period range of 0.001–100 s. The dimensionality analysis proved the validity of the 2-D assumption, and therefore a joint 2-D inversion of the TE and TM modes was undertaken constraining the modelling process according to a vintage resistivity log acquired for oil exploration. The 2-D model provides the first geoelectrical image of the structure and links the different lithologies to electrical properties. Results locate the main reservoir and seal units in the period range of 0.1–1 s. Thereby it is proved the validity of the method to supply a high resolution baseline model able to fully image the geoelectrical structure of the Hontomín site in the pre-injection state.

► First geoelectrical image of the subsurface of the Spanish TDP for CO2 storage.
► 22 magnetotelluric soundings provide a 2-D resistivity model of the Hontomín site.
► Reservoir and seal lithologies are linked to their electrical properties.
► Primary reservoir and seal units are located in the period range of 0.1–1 s.
► Results prove the validity of MT to characterize the site and get a baseline model.