Experimental Study on Disposition of Carbon Dioxide in Deep Stratum and Seabed

为了获得二氧化碳在深海和海底处置的基础数据，我们进行了以下实验。(1)将液态二氧化碳、花岗闪长岩和地下水密封于barnes型热液体系中，在100bar下加热至150℃。每隔一段时间采集样品溶液，采用AA、ICP-MS和离子色谱法进行分析。对反应后的岩石进行了x射线、扫描电镜和电子能谱分析。分析结果表明，实验溶液中钙含量迅速下降，表明碳酸钙在体系中有沉淀。这表明二氧化碳可以以碳酸钙的形式固定在深层加热地层中。(2)将试验结果与秋田县大町热区的现场试验数据进行了比较。在现场试验中，固体二氧化碳与地下水一起放入1000m深的花岗岩闪长岩钻孔中，加热温度为200℃。现场试验所得溶液的化学变化与本研究的实验数据吻合较好。(3)为了了解二氧化碳对海水成分的影响，在实验室进行了碳酸盐离子与海水的反应，并用EPMA对沉淀进行了分析。随着海水中碳酸盐浓度的增加，白云石或富镁方解石迅速沉淀，说明碳酸盐离子对海水成分的影响较大。本文的研究成果将有助于推进二氧化碳在深海和海底的处置技术进步。

In order to obtain fundamental data for disposition of carbon dioxide in deep stratum and seabed, we carried out the following experiments.(1) Liquid carbon dioxide, granodiorite and ground water were sealed into Barnes-type hydrothermal system and heated to 150℃ at 100bar. Sample solutions were collected at intervals and analyzed by AA, ICP-MS and ion-chromatography. The rock after the reaction was analyzed by X-ray, SEM and EPMA. The results of analysis showed that calcium decreased rapidly in the experimental solution indicating calcium carbonate precipitated in the system. This suggests that carbon dioxide can be fixed in deep heated stratum as calcium carbonate.(2) The experimental results were compared with the data of a field test which was carried out at Okachi thermal area in Akita Prefecture. In the field test solid carbon dioxide was put with ground water into a 1000m-deep drill hole in granodiorite heated at 200℃. The chemical change of the solutions from the field test well accord with the experimental data of this study.(3) In order to understand the effect of carbon dioxide to seawater composition, carbonate ion was reacted with seawater in laboratory and precipitates were analyzed by EPMA. With increasing carbonate concentration in seawater dolomite or Mg-rich calcite were quickly precipitated, suggesting that carbonate ion affect seawater composition strongly.The results of this study would be effective to make technical progress in carbon dioxide disposition to deep stratum and seabed.