The responses of electrical resistivity tool to CO2 dissolution in brine and carbon mineralization – Implication for Monitoring Underground CO2 Sequestration.

Evaluation of the reliability of CO2 monitoring techniques is a critical step in risk assessment ofany CCS project. Electrical resistivity survey has an edge over seismic survey as a tool to monitor CO2plume migration, mainly due to the insensitivity of the latter to CO2 saturation above 20%. However, theability of electrical resistivity sensors to track CO2 dissolution in aquifer brine and then carbonmineralization that occurs afterwards is still not very convincing as shown by the conflicting experimentaland field data published in the literature. The objectives of this paper include a review of publishedexperimental and field data, present more experimental data to clear some doubts and then use theknowledge gained therein to produce an electrical resistivity response model to the different geochemicalprocesses that take place in the life cycle of CO2 storage in underground aquifer formation. Here, threedifferent types of laboratory experiments are presented to enhance our understanding of the responses ofelectrical resistivity to: (1) CO2 plume migration in a saline aquifer, (2) CO2 dissolution in aquifer brine, (3)CO2 mineralization process in a carbonate rock. Laboratory flow and static experimental systems were setup, which consist of flow pumps, an industrial oven, pressure and temperature transducers, core (sample)holder, an electrical resistivity meter that is able to log electrical resistivity measurements at high pressureand high temperature, and a data logging computer for monitoring and storing the measured data. The threeexperiments showed that electrical resistivity: (1) is highly sensitive to CO2 plume migration (2) isinsensitive to CO2 dissolution in aquifer brine, (3) is sensitive to rock dissolution and the subsequentmineralization process. An explanation is provided why electrical resistivity is insensitive to CO2 dissolutionin aquifer brine. Also, a validation experiment was conducted to validate the response of electrical resistivityto carbon mineralization. Finally, an electrical resistivity response model was developed to describe thebehaviour of resistivity to the different geochemical processes during CO2 underground storage process.