報告書番号

N07

タイトル（和文）

大規模排出源近傍におけるCO2地中貯留可能性評価法‐深部帯水層貯留に向けた研究開発‐

タイトル（英文）

Evaluation method of CO2 geological storage near the large-scale emission sources in Japan -Research and development for deep aquifer storage-

概要 （図表や脚注は「報告書全文」に掲載しております）

温室効果ガス削減対策の一方策として，CO２地中貯留に向けた技術開発が国内外で進められている．現在，貯留サイト選定のための貯留可能性評価法の構築とそのための技術開発が必要と考えられている．当所では，これまでにわが国のCO２大規模排出源近傍に多く分布する背斜構造などの構造トラップを示さない非構造性帯水層へのCO2地中貯留の可能性検討を行ってきた．本報告書では，このような帯水層へのCO2貯留メカニズムの整理と貯留ポテンシャルの高い地域の抽出を行い，あわせて貯留可能性評価のための個別の技術，すなわち，地中貯留可能量評価法，移行挙動評価技術，地中挙動予測技術，化学的影響評価技術，についてその方法と事例を体系的に取りまとめた．

概要 （英文）

In order to develop evaluation method of CO2 geological storage suitable for Japanese geology and location of CO2 large-scale emission sources in Japan, we investigated the evaluation method of CO2 storage capacity, CO2 migration analysis and environmental impact, and CO2 monitoring technology. The principle results are shown as follows.
(1) The Pleistocene, Neogene and Palaeogene sedimentary rocks which deem to be suitable rocks for aquifer storage of CO2 in Japan are widely distributed under about 800m below ground around the shore of our country, but many of these sedimentary rocks are not having large-scale closure structure. The mechanisms of storage into these geologies and the evaluation method of theoretical storage capacity which suited the storage mechanism were shown, and geological surveys required for evaluation of storage capacity were systematically summarized.
(2) CO2 geologic storage needs a study on understanding of supercritical CO2 migration injected in deep underground rock with high pressure and temperature. A numerical model, which can treat dissolution of CO2 as a transient phenomenon, phase equilibrium using precise equation of state, and advection or diffusion of CO2, was developed. Measurement methods of input dataset for the numerical model, which include laboratory experiments and in-situ field experiments using borehole, were reviewed. An estimation of CO2 migration for 1,000 years was also demonstrated using geological and hydrological model determined by results of logging in a borehole and core testing in a stratified structure.
(3) As risks of environmental impact due to leakage from storage of CO2 in geological reservoirs are envisaged for a long period, a method needs to be developed to predict the impact due to leaked CO2. We focused upon chemical impacts on groundwater and rock due to gradual leakage of CO2 and developed a tentative method to estimate heavy metals and trace elements released from rocks in the presence of CO2. Preliminary accelerated batch experiments of CO2-water-rock reaction were demonstrated to estimate effects of CO2 dissolution into water on the release of such elements. The results showed that an effect of pH decrease due to CO2 dissolution depends on a kind of rock. Quantities and species of element which could be released from rocks also varied with a rock type. The method was capable to readily estimate chemical impact on groundwater in a case of dissolution of leaked CO2 into groundwater.
(4) One of the major issues in geological storage of CO2 is to monitor the migration and diffusion of CO2 in the reservoirs. We need to develop several kinds of monitoring method and establish a highly reliable monitoring method. Electrical method and self potential method are expected to monitor the CO2 migration. We conducted laboratory and field experiments, and the results suggest that there is high possibility to monitor the CO2 migration by these methods.

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