1. Study on CO₂ hydrate formation in sea-bed

CO₂ hydrate is one of stable phase in environment of sea-bed. We discuss the system, that seal layer will be formed by CO₂ hydrate injection in loose sea-bed, and large quantities of CO₂ will be sequestrate under the seal layer.

Investigation of CO₂ hydrate formation using glass model sediment

For discussion of CO₂ hydrate formation technology, CO₂ hydrate formation was observed in glass model sediment and the influence on liquid CO₂ migration was investigated.

The CO₂ hydrate formations were found in the environment less than 5°C. The permeability of liquid CO₂ was reduced by CO₂ hydrate formation. And we surveyed the sea bed area in Japan, which is possible to form the roofed seal layer with CO₂ hydrate. Suitable areas were found in around Hokkaido and the north area of Japan Sea.

Experiment of CO₂ hydrate stability in sea bed

CO₂ permeability through a roofed seal layer with CO₂ hydrate was rudimentary studied for the stability assessment and for the estimation of the sealing ability. It was experimentally researched whether the liquid CO₂ under the seal layer was permeable or not only by its buoyancy. A measurement technique was also developed for detecting precisely a small amount of seepage of CO₂. As a result, it was clarified that the sealing ability of the hydrate-layer was sufficient and that the liquid CO₂ could not permeate the artificial seal layer of glass beads (0.1-1.0mm in the averaged diameter) and of Toyoura-standard sands.

To understand the geophysical and geochemical dynamics of injected CO₂ and interactions with reservoir fluid, following data are required as basic data; the physical properties of CO₂ solution, the density, the viscosity and the solubility. With focused on this, an experimental investigation was carried out to directly measure those of CO₂ saltwater solution. The density was investigated using a magnetic suspension balance system, of which the error analysis was carried out.

2. Field Study on CO₂ Fixation by Deep Rock-bed

We have studied on the feasibility of CO₂ fixation and storage in the deep rock-beds, especially serpentinite. We investigated the weathered parts of a serpentinite rock mass in Hokkaido. At All observation points, several carbonate minerals in accompany with the serpentinite were found.

The formation ages of carbonate minerals have been evaluated by measurements of C-14 isotope. The latest age of 110±0.5 years was obtained. The formation temperatures were estimated to be a normal temperature by oxygen isotope ratio (¹⁸O/¹⁶O).

The capability of CO₂ storage using the serpentinite rock-beds is evaluated to about 700 million tonnes, assuming that the effective storage space in the rock mass is as low as 0.03%, and that density of supercritical CO₂ is 500kg/m³.

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