Articles | Volume 7, issue 3
Solid Earth, 7, 943–958, 2016

Special issue: From orogenesis to geoscience in the service of society: the...

Solid Earth, 7, 943–958, 2016

Research article 09 Jun 2016

Research article | 09 Jun 2016

Joint interpretation of magnetotelluric, seismic, and well-log data in Hontomín (Spain)

Xènia Ogaya1, Juan Alcalde2, Ignacio Marzán3, Juanjo Ledo4, Pilar Queralt4, Alex Marcuello4, David Martí3, Eduard Saura3, Ramon Carbonell3, and Beatriz Benjumea5 Xènia Ogaya et al.
  • 1Dublin Institute for Advanced Studies, School of Cosmic Physics, Dublin 2, Ireland
  • 2Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, UK
  • 3Institute of Earth Sciences Jaume Almera ICTJA-CSIC, Barcelona, Spain
  • 4GEOMODELS Research Institute, Dept. Dinàmica de la Terra i de l'Oceà, Facultat de Geologia, Universitat de Barcelona, Barcelona, Spain
  • 5Institut Cartogràfic i Geològic de Catalunya ICGC, Parc de Montjuïc, 08038 Barcelona, Spain

Abstract. Hontomín (N of Spain) hosts the first Spanish CO2 storage pilot plant. The subsurface characterization of the site included the acquisition of a 3-D seismic reflection and a circumscribed 3-D magnetotelluric (MT) survey. This paper addresses the combination of the seismic and MT results, together with the available well-log data, in order to achieve a better characterization of the Hontomín subsurface. We compare the structural model obtained from the interpretation of the seismic data with the geoelectrical model resulting from the MT data. The models correlate well in the surroundings of the CO2 injection area with the major structural differences observed related to the presence of faults. The combination of the two methods allowed a more detailed characterization of the faults, defining their geometry, and fluid flow characteristics, which are key for the risk assessment of the storage site. Moreover, we use the well-log data of the existing wells to derive resistivity–velocity relationships for the subsurface and compute a 3-D velocity model of the site using the 3-D resistivity model as a reference. The derived velocity model is compared to both the predicted and logged velocity in the injection and monitoring wells, for an overall assessment of the computed resistivity–velocity relationships. The major differences observed are explained by the different resolution of the compared geophysical methods. Finally, the derived velocity model for the near surface is compared with the velocity model used for the static corrections in the seismic data. The results allowed extracting information about the characteristics of the shallow unconsolidated sediments, suggesting possible clay and water content variations. The good correlation of the velocity models derived from the resistivity–velocity relationships and the well-log data demonstrate the potential of the combination of the two methods for characterizing the subsurface, in terms of its physical properties (velocity, resistivity) and structural/reservoir characteristics. This work explores the compatibility of the seismic and magnetotelluric methods across scales highlighting the importance of joint interpretation in near surface and reservoir characterization.

Short summary
This paper explores the compatibility of seismic and magnetotelluric methods across scales highlighting the importance of joint interpretation in reservoir characterisation. The combination of the two methods together with well-log data at the Hontomín CO2 storage pilot plant (Spain) allowed a detailed characterisation of the shallow subsurface and defined the structural and fluid flow characteristics of the existing faults, which are key aspects for the risk assessment of the site.