Effects of impurities H2S and N2 on CO2 migration and dissolution in sedimentary geothermal reservoirs

Abstract CO2 geological storage is a key technology for reducing greenhouse gas emissions. But merely injecting CO2 into sedimentary strata has high costs and no direct economic benefit. A more cost-effective and environment-friendly way is storing and utilizing CO2 in deep sedimentary reservoirs for heat extraction. However, the effects of ubiquitous impurities on the sequestration safety and heat extraction performance of CO2 in high-temperature reservoirs, are unclear. In this study, we have performed numerical simulations of multiphase flow, solute transport, and heat conduction at reservoir temperature 50–250 °C, to reveal the effects of two common impurities (i.e., H2S and N2) on the migration, dissolution and thermal absorption of CO2 in sedimentary geothermal reservoirs. It is found that, for higher reservoir temperature, the impurity N2 leads to smaller promotion on the migration of gas phase, but retains the acceleration effect on the cooling in reservoir. Above 150 °C, the deviations on the gas phase migration velocity and the CO2 dissolution efficiency caused by 10 mol% N2 are less than 12%. Meanwhile, the 10 mol% N2 can increase the total heat absorbed from reservoir by about 40% at least. It means that N2 has the potential to benefit a CO2 plume geothermal system significantly without distinct risks. Besides, it is also found that the CO2 dissolution efficiency can be increased and decreased by H2S and N2 through partitioning phenomenon, respectively.