Experimental and numerical modeling of CO 2 leakage in the vadose zone

This study presents the experimental and modeling results of CO 2 injection and transport in the vadose zone performed in PISCO2 facilities at the ES.CO2 center in Ponferrada (North Spain). During 46 days of experiments, 62.10 kg of CO 2 were injected through 16 micro‐injectors in a 35 m-super-3 experimental unit filled with sandy material. Monitoring and mapping of surface CO 2 flux were performed periodically to assess the evolution of CO 2 migration through the soil and to the atmosphere. Numerical simulations were run using TOUGH2 code with EOS7CA research module considering two phases (gas and liquid) and three components (H 2 O, CO 2 , air). Two layers (sand, gravel) and atmosphere boundary were implemented taking into account heterogeneous soils, homogeneous soil, rainfall, temperature, and liquid saturation to allow a better understanding of CO 2 behavior in the vadose zone. This combined experimental and modeling approach shows that CO 2 leakage in the vadose zone quickly comes out through preferential migration pathways and spots with the ranges of fluxes in the ground/surface interface from 2.5 to 600 g·m-super-−2·day-super-−1. This gas channeling is mainly related to soil compaction and climatic perturbation. This has significant implications for design‐adapted detection and monitoring strategies of early leakage in commercial CO 2 storage. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd