CO2 sequestration scenarios: challenges and opportunities for EM exploration techniques at Hontomín

The geological storage of CO2 is presented as a transitory solution to reduce the human emission of CO2. To be efficient and safe, it is required to obtain a very good knowledge of the subsurface and to have tools to control the evolution of the CO2 sequestrated into reservoirs. Geophysical techniques are essential for characterizing and to monitoring the storage sites. The paper presents an overview of existing electromagnetic methods which have been conducted at the Hontomín CO2 storage site (in Spain) during the past few years. These studies cover numerical simulations and geophysical campaigns at different scales and with different electromagnetic techniques: the magnetotelluric method, control source electromagnetic and electrical resistivity tomography at lab-core scale. The objective of the paper is to offer a critical review of the EM methods in meeting challenges related of achieving high resolution for deep targets and in a relatively noisy environment. We conclude with the lessons learnt from the Hontomín case study. Research for new natural resources as well as new complex pollution problems require new efforts from scientists, in particular the environmental earth sciences community, to analyse the problems and to find appropriate solutions and tools. In this way, advances and improvements in geophysical exploration techniques depend, in some part, on the challenges of these new problems. The evolution of the electromagnetic and electric methods (EM) shows how they have broadened their application fields when these demanding tasks have been faced. Recent studies (i.e. Constable, 2010; Strack, 2014; Muñoz, 2014; Streich, 2016) review the main contributions of these methods in specific fields such as geothermal and hydrocarbons exploration and monitoring and point out their potential as well as some future directionsin each field. EM methods play an important role in these fields given the resistivity dependency on temperature and/or on the presence of fluids.