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

Abstract Magnetotelluric (MT) data provided a two-dimensional (2-D) resistivity model of the subsurface of the Technology Demonstration Plant (TDP) located in Hontomin (Burgos, Spain) for geological storage of CO 2 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 Hontomin site in the pre-injection state.