著者

佐々木 宗建 徂徠 正夫 奥山 康子 村岡 洋文

出版者

一般社団法人 日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.38, no.5, pp.175-197, 2009 (Released:2009-11-26)

参考文献数

48

被引用文献数

2 2

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Water qualities and occurrence of precipitates in 10 hot and mineral springs with large calcareous deposits in Japan were investigated in order to elucidate geochemical conditions of the precipitation of carbonate minerals and water-rock interactions in their reservoirs. Chemical analyses of water samples have revealed that the spring waters were rich in NaHCO3 and CO2 components. Out of 10 springs investigated, 2 springs contain Ca and CO2-related soluble components with genetic relations to the dissolution of limestone underground; 4 springs also enriched in Ca were green-tuff type affected by gypsum dissolution. Other springs poor in SO4 component have geochemical characteristics suggesting the contribution of deep-seated fluid. The pH of reservoir fluids is considered to be buffered by CO2-HCO3 speciation. This chemical condition probably promotes rock alteration including dissolution of calcite and plagioclase, resulting in formation of large calcareous deposits in the fields studied. The calcareous precipitates consist only of calcite in three fields with relatively low water temperatures; the other deposits contain aragonite with calcite possible due to their formation at high temperatures and high concentrations of Mg, Mn and SO4 in spring waters. From a comparison of water chemistry at the points of precipitation, logarithmic critical saturation indices (SI) are empirically derived to be 0.7-0.9 for calcium carbonate and over 3.5, 0.5, 1.2 and 3.4 for dolomite, magnesite, siderite and dawsonite, respectively. Distribution coefficients of Sr and Mg between spring water and precipitates indicate that calcareous precipitates were formed near equilibrium conditions.   The possible ware-rock interaction processes elucidated in this study should be taken into account for geochemical modeling of CO2 geological reservoirs. The empirical values of SI, which are all positive for major carbonate minerals, can be the most important finding because geochemical simulation previously conducted commonly assumed precipitation at the point of saturation (SI=0).

著者

徂徠 正夫 後藤 宏樹 杉原 光彦 西 祐司 中尾 信典

出版者

一般社団法人 資源・素材学会

雑誌

Journal of MMIJ (ISSN:18816118)

巻号頁・発行日

vol.137, no.4, pp.46-50, 2021-04-30 (Released:2021-04-28)

参考文献数

17

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Toward the implementation of geological CO2 storage, cost reduction of CO2 monitoring during and after injection into targeted reservoirs is the key issue. The continuous gravity measurement using a superconducting gravimeter, which has been applied to the demonstration project site in Japan ahead of the rest of the world, has a potential to resolve the issue from the viewpoint of a complement to the high-cost seismic survey. The concept is such that the continuous gravity measurement is substituted for constant monitoring and that the use of seismic survey could be limited only when any anomaly is detected. The comparison of the monitoring cost after the completion of CO2 injection indicated that applying gravity measurement can reduce costs by up to 15 to 50% of the seismic cost. The current detection limit of gravity change is around 1 μGal based on the application result in the coastal area in Japan. However, the time series analysis using pseudo gravity data suggested the possibility of anomaly detection even below the detection limit. Further improvement of analysis precision would lead not only to more rapid and more reliable anomaly detection but also to contribution to the cost reduction during the CO2 injection period.