A case study of using cosmic ray muons to monitor supercritical CO 2 migration in 1 geological formations

15 In carbon dioxide (CO2) geological storage, the monitoring of the injected CO2 migration in 16 underground storage is essential to understanding storage process and ensuring storage safety. An 17 effective monitoring system will be required for decades into the future during storage phase to 18 indicate the location where the injected fluids have extended to. A novel radiographic probing 19 technique using naturally occurring cosmic ray muon radiations was introduced in recent years as 20 a promising continuous and cost-effective candidate method. This method utilizes the ability of 21 different materials to attenuate muons as the detection property. The feasibility of this technique 22 still needs to be investigated in terms of higher simulation accuracy, the intrinsic spatial resolution, 23 and response sensitivity for storage with impurities. In this study, simulations are performed to 24 understand the sensitivity of this method in responding to the presence of the injected fluids in 25 saline aquifer formations. The energy spectrum of the cosmic ray muons for different zenith angles 26 at sea level is sampled according to the modified Gaisser’s formula. The muon propagation 27 process has been simulated with high fidelity by detailed description of different materials 28 involved in the deployed geological model. The muon attenuation along different paths carries 29 information on the interior of a monitored region and the muon scattering effect may lower the 30 accuracy to locate the fluids. The intrinsic spatial resolution of this method is thus analysed and 31 found to be at a scale of several meters. This method aims to provide the basis for understanding 32 the injected fluids behaviour. The simulations show that the method is feasible and the injected 33 fluids in saline aquifers can be identified with a high sensitivity. 34