採油増進回収およびCO₂地中貯留・固定化に対するケイ酸ナトリウム水溶液を用いた複合システムの提案

抄録

In this paper, the technical challenges in enhanced oil recovery using a sodium silicate solution as a multi-purpose chemical are introduced to enhance oil recovery by alkaline flooding and prevent channeling flows through high permeability layer/regime and geological storage of carbon dioxide（CO₂）. We have focused on the sodium-metasilicate-hydrates（Na₂SiO₃.9H₂O; S-MS）from many types of chemicals. Firstly, oil properties with S-MS solution（pH12-13）are presented to carry out alkaline flooding based on measurement results of interfacial tension（IFT）, contact angle and emulsion formation with oil considering reservoir-water salinity. Secondary, in-situ gel formation using the reaction between S-MS solution and dissolved CO₂ is introduced as a blocking agent in high permeability flow-passes in an oil reservoir with different permeability layers. Both of Raman and SEM-EDS spectroscopy revealed that the formed gel is a sodium carbonate type gel（SC-gel）. Physical characteristics of SC-gel were investigated in respect of S-MS concentration, temperature and CO₂ gas pressure. The blocking effect was evaluated by threshold pressure gradient and gas permeability by forming in-situ SC-gel in a sandstone core. Then the core flooding test using heterogeneous core consists from two sandstones cores with different permeabilities was carried out to find improvements in oil recovery by alkaline flooding using S-MS solution and blocking effect by the in-situ gel formation with CO₂ gas injected. Furthermore, a new system（a kind of Carbon-dioxide capture, utilization and storage）using the S-MS solution is proposed for CO₂ capture, usage and geological storage into relatively shallow oil reservoirs or aquifers meet a safe and economical onshore CO₂ sequestration. Furthermore, it is also expected that the in-situ gel formation between S-MS solution and CO₂ gas emitted from fires of peat layer or coal seam has a possibility to extinguish large scale fires contributing global warming.