Study of assessment techniques of seal performance

Development of Assessment Techniques of Seal Performance

<FY2006>

Summary
To assess the influence of permeability by CO₂-rock interaction, the flow through test was performed by using of reservoir rock (sand stone). Also we developed a CO₂-rock experimental system for high pressure. Preliminary test was performed and discussed to assessment techniques of seal performance by seismic tomography.

Influence of CO₂-rock interaction and storage of CO₂ in reservoirs

(1) Research of influence of permeability by CO₂-rock interaction

Tuff matter sandstone was selected in imitation of reservoir rock, a kind of sandstone, containing the anorthite (CaAl₂Si₂O₈) and high permeability.

CO₂ dissolution water (4.7wt%) flowed through the core-rock sample by pressure at 80°C during about 2 month. Permeability was monitored by flow rate, and the alteration of chemical property.

In the result, the permeability decreased one-tenth. This result seemed to require further research and discuss. The ions of K, Na, Ca, Mg and Si were leached from the rock. It was found that leaching of Na, Ca and Mg ions are promoted by CO₂ solution. Alterations of mineral component and physical properties (porosity etc.) were not observed.

Also, the dissolution of anorthite was observed at the surface and its dissolution rate was estimated to be less than 7.1E-16 mol/cm²/sec.

(2) Study of assessment techniques of seal performance by seismic tomography.

We developed a CO₂-rock experimental system for the investigation of seal performance and influence of CO₂-rock interaction. In this system, CO₂ behavior in rock sample can be observed by seismic tomography, and threshold pressure can be measured by control of injection and pore-water pressure.

Preliminary test was performed using the calcareous silt rock from Nagaoka test site. The behavior of injected CO₂ was monitored by seismic tomography. Also, the threshold pressure was measured.