Geoelectrical Remote System for Monitoring Shallow Subsurface CO2 Migration

The implementation of the first CO2 MMV field lab in Brazil, located in Florianópolis, Santa Catarina state, offered an excellent opportunity for running controlled release experiments in a real open air environment. After three CO2-controlled release experiments run from 2011 up to 2015, PETROBRAS, the national oil company that is sponsoring the project, has launched a new challenge. The company stimulated the implementation of a new Brazilian experimental site located in a geologically more complex conditions and more challenging from a technological point of view. The choice of an area inside PUCRS campus, in Viamão Rio Grande do Sul state, was motivated by a predominantly clay subsoil and the privileged location of the site in terms of logistics and security, as the project houses high-tech equipments with significant cost. The purpose of this work is to present the results obtained by the geoelectrical remote time lapse using 3D electrical imaging technique to the monitoring of CO2 migration in both saturated and unsaturated clay-rich sediments in Viamão site, which is lithologically different from the Florianópolis field lab, composed of sandrich sediments. The CO2-controlled release occurred in 2016, covering an subsurface area of approximately 2.925 m. The CO2 was continuously injected through an injection well, at 3 m deep, in a period of 31 days (24 hours/day), at a rate ranging from 5 to 20 kg / day, totalizing 346 kg of injected CO2. While the CO2 was been injected, 3D electrical images using dipole-dipole array, were acquired in a daily base, totalizing 46 consecutive days (including periods before and after injection have been suspended). 3D (tridimensional) and 4D (time-lapsed) electrical imaging produced images up to 17 m below the surface. Remote monitoring has been used for the continuous characterization of the soil/sediment geoelectric responses, significantly increasing the accuracy with respect to the external effects that interfere in the geoelectric responses, such as excessive precipitation and changes in the injection rate. Comparison of post-injection electrical imaging results with pre-injection images