Large-scale storage of carbon dioxide in saline aquifers may cause considerable pressure perturbation and brine migration in the deep formations, which may give rise to a significant influence on the regional groundwater system. With the help of parallel computing techniques, a comprehensive, large-scale numerical simulation of CO 2 geologic storage that predicts not only CO 2 migration but also its impact on regional groundwater flow was performed. As a case study, a hypothetical industrial-scale CO 2 injection in the Tokyo Bay, which is surrounded by the most industrialized area in Japan, was considered, and the impact of down-dip CO 2 injection on up-dip near-surface aquifers was investigated. A regional hydrogeological model with an area of about 60km×70km around the Tokyo Bay was discretized into about 10 million gridblocks. To solve the high-resolution model efficiently, we used a parallelized multiphase flow simulator TOUGH2-MP/ECO2N on a world-class high performance supercomputer in Japan, the Earth Simulator. In the simulation, CO 2 was injected into a storage aquifer at about 1km depths under the Tokyo bay from 10 wells with the total rate of 10 million tons/year for 100 years. Through the model, regional groundwater pressure build-up and seepage changes at land surface are examined. The results suggest that even if containment of CO 2 plume is ensured, pressure buildup in the order of tens of meters can occur in shallow confined layers of extensive regions including urban inlands.
Three different-scale electromagnetic (EM) measurements have been performed in the Kujukuri coastal plain, southeast Japan, to investigate the distribution of saline groundwater. The three techniques were audio-frequency magnetotelluric (AMT), transient electromagnetic (TEM), and small loop-loop EM measurements. The resistivity sections estimated from these data sets reveal three independent resistivity distributions extending to different depths. The AMT method reveals a regional-scale resistivity distribution across the plain to a maximum depth of approximately [Formula: see text] and the existence of deep conductive zones, which are inferred to be associated with fossil seawater trapped in a Pleistocene formation. The TEM results show a medium-scale resistivity distribution to depths of approximately [Formula: see text], in which two shallow conductive zones are recognized. It is concluded that these features are caused by present seawater intrusion and high-salinity salt-marsh deposits formed during sporadic marine regressions. The small loop-loop EM method provided a shallow resistivity profile that highlights the conductive salt-marsh deposits and resistive sandy ridges. Although these resistivity sections correspond to different depth ranges, the overlapping portions of the sections are very consistent with one another. These EM methods are useful in detecting and interpreting important resistivity features. Taking the geologic evolution of the coastal plains into consideration is crucial when interpreting resistivity profiles such as these, and our results suggest that the presence of fossil seawater is an important factor controlling resistivity at a variety of depths.
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