Experimental study of artificial barrier formation to reduce the leakage risk on geological CO2 storage

Abstract:

On geological CO₂ storage, the most likely leakage path is microfractures around boreholes. One of effective countermeasures against such a leakage risk includes the addition of CO₂-fixation agent, which forms solid film to infill microfractures around a borehole, at the completion of CO₂ injection. To verify the effectiveness of such an artificial barrier formation, this study performed CO₂-fixation experiments as carbonates or other solid materials under flow-through conditions of spring waters.

The Berea sandstone with a cylindrical shape, whose diameter and height were respectively 14 mm and 10 mm, were used as an alternative to a reservoir rock. These were set in a reaction tube and exposed to the flowing solution under the condition of around 57ºC and 0.5 MPa. The solution contained the sodium hydroxide (NaOH)-added and sodium silicate (Na₂O· nSiO₂)-added spring waters, in addition to the original spring water. I examined the influence of presence or absence of CO₂ in each solution. During experiments, the drainage water was stored in a measuring cylinder, and then the flow rate was calculated from an average of water volume within predetermined time.

All experiments showed more or less the reduction of flow rate with time. In the case of NaOH-added solutions, only the test without CO₂ injection formed the carbonate layer at the edge plane of a sample. This caused a larger decrease in flow rate. The comparison of experiments with and without CO₂ suggests that the alkaline NaOH promoted the carbonate precipitation whereas that the CO₂ injection suppressed the carbonate formation because of the pH reduction. On the other hand, the Na₂O· nSiO₂-added solution produced the tight solid material within a tube immediately. This stopped the water flow thoroughly. Therefore, the result revealed that the use of Na₂O· nSiO₂ proposed by Ito et al. (2014) is available also for CO₂-containing natural waters. The future problem includes the exploration of optimum conditions, such as the concentration of the additive and the timing of its injection, based on numerical simulations plus additional field experiments.

This presentation is based on results obtained from a project (JPNP18006) commissioned by the New Energy and Industrial Technology Development Organization and the Ministry of Economy, Trade and Industry of Japan.