文摘
This study focused on the target injection layers of deep saline aquifers in the Shiqianfeng Fm. in the Carbon Capture and Sequestration (CCS) Demonstration Projects in the Ordos Basin, northwestern China. The study employed a combination method of experiments and numerical simulation to investigate the dissolution mechanism and impact factors of COb>2b> in these saline aquifers. The results showed (1) COb>2b> solubility in different types of water chemistry were shown in ascending order: MgClb>2b>-type water < CaClb>2b>-type water < Nab>2b>SOb>4b>-type water < NaCl-type water < Nab>2b>COb>3b>-type water < distilled water. These results were consistent with the calculated results undertaken by TOUGHREACT with about 5% margin of error. COb>2b> solubility of Shiqianfeng Fm. saline was 1.05 mol/L; (2) compared with distilled water, the more complex the water’s chemical composition, the greater the increase in HCOb>3b>−concentration. While the water’s composition was relatively simple, the tested water’s HCOb>3b>−concentrations were in close accord with the calculated value undertaken by the TOUGHREACT code, and the more complex the water’s composition, the poorer the agreement was, probably due to the complex and unstable HCOb>3b>− complicating matters when in an aqueous solution system including both tested HCOb>3b>−concentration and calculated HCOb>3b>−concentration; (3) the COb>2b> solubility in the saline at the temperature conditions of 55 °C and 70 °C were 1.17 and 1.02 mol/L. When compared with the calculated value of 1.20 and 1.05 mol/L, they were almost the same with only 1 and 3% margin of error; concentrations of HCOb>3b>− were 402.73 mg/L (0.007 mol/L) and 385.65 mg/L (0.006 mol/L), while the simulation results were 132.16 mg/L (0.002 mol/L) and 128.52 mg/L (0.002 mol/L). From the contrast between the tested data and the calculated data undertaken by the TOUGHREACT code, it was shown that TOUGHRACT code could better simulate the interaction between saline and COb>2b> in the dissolution sequestration capacity. Therefore, TOUGHREACT code could be used for the inter-process prediction of COb>2b> long-term geological storage of COb>2b>; (4) The Ca2+ concentration and SOb>4b>2−concentration in saline water had less effect on the solubility of COb>2b> and HCOb>3b>−concentration. In addition, TDS and pH values of saline affected not only the solubility of COb>2b>, but also the conversion of COb>2b> to HCOb>3b>− due to that they can affect the activity and acid-base balance. So in fact, we just need to consider that the TDS and pH values are main impact factors in the dissolution sequestration capacity of COb>2b> geological sequestration in deep saline aquifers.
