Density Measurements of Supercritical CO2 + Dagang Brine for CO2 Geological Storage

Abstract

Carbon dioxide capture and storage (CCS) in saline aquifers has been considered as one possible means of reducing greenhouse gas emissions and mitigating climate change. The density difference of 0.1 kg·m·-3 is sufficient to drive a natural CO2-bearing solution to either sink or buoy, which is one of the main factors affecting the safety of CO2 storage. The density of CO2 aqueous solution is also necessary to estimate the storage capacity of the storage formation. Therefore, the density change due to the dissolution of CO2 is essential for simulation of CO2 sequestration process and CO2 migration in the formation.The density experiments were performed using a magnetic suspension balance (MSB) manufactured by Rubotherm Priizisionsmesstechnik GmbH. The measuring conditions (temperature, pressure and measuring medium) can be artificially controlled because the balance and the measuring cell were completely isolated. Taking full advantage of the high accuracy and stability of the magnetic suspension balance, this paper reported the experimental densities of CO2-brine solution from Dagang Oilfield reservoir. The densities of CO2 brine mixture were measured in CO2 geological storage conditions such as 313K-353K, 10-18MPa and CO2 mole fraction in solution up to 0.0123. The effects of different conditions on CO2 aqueous solution density were analyzed based on the experimental data. It was found that the density of CO2 aqueous solution increases linearly with the pressure and the slopes at different concentrations are almost the same at a certain temperature. We also found that the dissolution of CO2 in brine will increase the density of aqueous solution in our experimental conditions. And at a constant pressure, the density of CO2 aqueous solutions increases with increasing CO2 concentration almost linearly in the experimental range. It provides systematic experimental density data for Tianjin Dagang CCS project.