09:00 〜 09:15
[HSC04-01] Altered/unaltered basalt-brine-CO2 gas interactions and dissolution mechanisms at moderate temperatures
キーワード：CO2固定、変質玄武岩、塩水、溶解
Mineralization of CO2 to water-insoluble carbonates using Mg/Ca-rich rocks such as basalt is one of the most promising methods for large-scale CO2 storage and is being increasingly studied. Since not a few oil and gas fields are associated with basaltic formations such as at the Sea of Japan side of the Northeast Japan Arc, using existing wells in such basaltic formations for CO2 storage is both technically and economically favourable. However, the basaltic rocks in oil and gas reservoirs have often been altered under hydrothermal conditions, and the feasibility and reactivity of using altered basalt for CO2 mineralization are still in doubt. This study investigated the potential dissolution mechanisms of both altered/unaltered basalt in brine or Milli-Q water-CO2 gas (5 MPa) systems through laboratory batch experiments conducted under conditions analogous to the realistic reservoir environments (100 ℃).
Experimental results show that the reactivity of altered basalt is not lower than that of unaltered one, and their dissolution behaviours show a big difference. Although more Mg and Ca were extracted from unaltered basalt than altered basalt in the Milli-Q water system within 15 days, in the brine system that simulated the real reservoir condition, the rate of Mg extraction from altered basalt is faster, reached 2.8×10-11 mol m-2s-1, which is 1.7 times higher than that from unaltered basalt; meanwhile, Ca extraction rate did not show a significant decrease. The dissolved Mg is found mainly from smectite in altered basalt but from orthopyroxene in unaltered basalt, while Ca is from plagioclase and clinopyroxene for both altered and unaltered basalt. The significant dissolution of smectite in altered basalt in brine systems potentially helps to create pathways for CO2-containing brine and to increase the reactivity of the surrounding minerals such as clinopyroxenes for CO2 storage.
Experimental results show that the reactivity of altered basalt is not lower than that of unaltered one, and their dissolution behaviours show a big difference. Although more Mg and Ca were extracted from unaltered basalt than altered basalt in the Milli-Q water system within 15 days, in the brine system that simulated the real reservoir condition, the rate of Mg extraction from altered basalt is faster, reached 2.8×10-11 mol m-2s-1, which is 1.7 times higher than that from unaltered basalt; meanwhile, Ca extraction rate did not show a significant decrease. The dissolved Mg is found mainly from smectite in altered basalt but from orthopyroxene in unaltered basalt, while Ca is from plagioclase and clinopyroxene for both altered and unaltered basalt. The significant dissolution of smectite in altered basalt in brine systems potentially helps to create pathways for CO2-containing brine and to increase the reactivity of the surrounding minerals such as clinopyroxenes for CO2 storage.