Geological Reservoir Characterization and Modelling of a CO2 Storage Aquifer: A Case Study of the Nagaoka Site, Japan

Abstract Site characterization is critical for safe and effective geological storage of CO2 because geological heterogeneity affects reservoir quality, plume migration, and trapping. This study shows geological characterization and modeling of a CO2 storage aquifer near Nagaoka, Japan. Core and well-logging analysis show that the target aquifer consists of deltaic deposits, which are characterized by a fining-upward to coarsening-upward succession that has developed on a ravinement surface. The target aquifer is attributed to prodelta and deltafront deposits. A geostatistical method known as sequential Gaussian simulation with collocated cokriging was applied to generate a spatial distribution of petrological and physical properties including shale volume, porosity, and permeability. The simulation was performed using well-log data as a primary variable and seismic-derived porosity data as a secondary variable under the constraints of correlation coefficient between variables. Simulated models showed that impermeable fine-grained deposits are distributed toward the east. This trend can explain the fact that breakthrough has not been observed at an observation well located farthest to the west from the injection well, IW-1. This result is consistent with previously proposed paleogeographic interpretations that show that detrital particles are transported from east to west at the Nagaoka site.