Deep groundwater of reservoir depth and its potential roles in geochemical CO2 trapping: Toward open aquifer CO2 storage in Japan

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Okuyama, Yasuko; Sorai, Masao; Sasaki, Munetake; Kaneko, Nobuyuki; Muraoka, Hirofumi; Yanagisawa, Norio; Tosha, Toshiyuki
Holding Date 04 October 2008

As the climatic effect of global warming has become sensible, a need for immediate action for CO2 emission reduction is widely recognized in these days. Geologic storage of CO2 to a deep saline aquifer is considered to be one of the most feasible measures. Notably, the measure of open aquifer storage recently attracts attention in Japan in which large point sources of CO2 are concentrated in coastal areas underlain by young sediments suitable for this way of CO2 sequestration. Geological Survey (GSJ), AIST, has been conducting a three-year research project on open aquifer CO2 storage, taking the Tokyo Bay area as a model field. This paper summarizes geochemical studies in GSJ/AIST concerning to open aquifer CO2 storage. Our studies include following sub-themes; 1) the natural analogue studies, such as the geochemistry and rock-water interaction in CO2-bearing springs and diagenetic changes of sedimentary rocks, 2) geochemical study of deep groundwater in young sedimentary basins for the assessment of CO2 solubility potential, 3) geochemical simulation and experiments in chemical systems of underground reservoirs. Among them, the geochemical study on Japanese groundwater in the reservoir depth is noteworthy. Groundwater is important as a medium of solubility trapping; the presence of groundwater acidified by CO2 promotes alteration of mineral grains in the reservoir rock to open a way toward eventual mineral trapping. We have been collecting chemical data of groundwater to set up a database (theپh formation-water databaseپh) for the evaluation of water quality from the view point of CO2 trapping.
The database indicates the presence of two distinct types of deep groundwater having peculiar characters possibly inherited from the ancient water in the place of deposition of host sedimentary strata. The database also indicates that deep groundwater in 10 important areas in Japan is generally dilute in composition suggesting its high potential of CO2 solubility. Nevertheless, some of the soluble components in deep groundwater show high concentrations as compared to that in average sea water. The high concentration of CaO and SiO2 in deep groundwater strongly suggests a progress of rock-water interaction during burial of host sedimentary strata. Stratigraphic control of Cl contents are also found in deep groundwater of so-called پgGreen tuffپh region in which the maximum Cl concentration lies in the middle of stratigraphy occupied by lowermost Pliocene marine sediments.