Abstract
二酸化炭素地中貯留における地球化学反応特性について― 長岡実証試験サイトの地層水分析例―
Geochemical Aspects of a Geological Storage of CO2 : A Case Study Based
on a Formation Water Analysis at the Nagaoka Pilot-scale CO2 Injection
Site
地学雑誌, 117, 4, 753-767, 2008.
三戸 彩絵子, 薛 自求, 大隅 多加志
To evaluate the long-term behavior of a CO2 storage site, it is necessary
to understand the geochemical reactions induced by CO2 injection into the
water in an aquifer. We observed changes in the chemical composition of
the formation water at the Nagaoka CO2 storage site, Japan, where a total
of 10,400 tonnes of CO2 was injected into a 12-m-thick sandstone section
of the Haizume Formation located at a depth of 1,100 m. The formation water
was collected from the CO2 injection well during a pumping-up test carried
out before the injection. Before the injection, the total dissolved solid
in the sampled water was 8,000 ppm, indicating that 50,000 ppm of CO2 can
be dissolved maximally in the formation water due to its solubility. After
the CO2 injection, the Cased Hole Dynamics Tester （CHDT） tools sampled
formation fluids by penetrating casing, and plugging the test hole in a
single trip at the depths determined by the well logging. The fluid sample
collected at a depth of 1114.0 m was almost free CO2. The other two fluid
samples from depths 1108.6 m and 1118.0 m were mainly the formation water.
At the depth of 1118.0 m, we observed an increase in the concentration
of HCO3 due to the dissolution of injected CO2. Concentrations of Ca, Fe,
Si, Mg and Mn also increased. These elements were potentially provided
by the dissolution of hornblende, serpentine, pyroxene, chlorite, and gypsum.
In particular, Ca, Mg, and Fe are important to neutralize acidified water
and to fix CO2 as a carbonate.
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