Effects of impurities N2 and O2 on CO2 storage efficiency and costs in deep saline aquifers

Carbon capture and storage (CCS) is one of the key technologies for reducing CO2 emissions, but it has suffered from the high costs for the purification of captured CO2 streams. Storing CO2 with two major impurities (i.e., N-2 and O-2) in geological formations would be more economical; however, the cost savings might be offset by the reduced CO2 storage efficiency. To understand the relationships between the reduced CO2 storage efficiency and the CO2 storage costs in deep saline aquifers, the effects of impurities N-2 and O-2 on the CO2 storage efficiency and CO2 storage costs in deep saline aquifers are evaluated. We established a 2D model by developing a new module incorporated into TOUGH2, to simulate the migration and dissolution of CO2-N-2-O-2 mixtures in aquifers based on the hydrogeological conditions of the Shenhua CCS site in China. It is found that the partitioning between CO2 and the impurities during migration can reduce CO2 storage efficiency by raising impurity concentrations in gas phase. But higher pressure and temperature in reservoirs can alleviate the reduction of CO2 storage efficiency, while retaining the benefit of the impurities on the CO2 dissolution efficiency. With 10 mol% N-2, the CO2 storage efficiency is decreased by at least 32%, while the CO2 storage cost in saline aquifers is increased less than 0.01 US $/t CO2.

Automated summary

The study evaluated the effects of impurities N-2 and O-2 on the CO2 storage efficiency and costs in deep saline aquifers, finding that higher pressure and temperature can alleviate the reduction in CO2 storage efficiency while maintaining the benefits of impurities on CO2 dissolution efficiency. Despite a decrease of at least 32% in CO2 storage efficiency with 10% N-2, the increase in CO2 storage costs in saline aquifers was less than 0.01 US $/t CO2.