The solubility of supercritical CO2 into pure water and synthetic Utsira porewater

This report describes work undertaken at the British Geological Survey (BGS) that forms part of the international SACS (Saline Aquifer CO2 Storage) project. The SACS project aims to monitor and predict the behaviour of injected CO2 in the Utsira Sand reservoir at the Sleipner field in the northern North Sea, using methods that include; time-lapse geophysics, modelling its subsurface distribution and migration, and simulating likely chemical interactions with the host rock. This report aims to provide a limited amount of CO2 solubility data to help constrain geochemical modelling activities, and to further our understanding of how much of the injected CO2 will dissolve into the Utsira formation water. The experimental study was undertaken in the Hydrothermal Laboratory of the BGS, where a range of measurements were made using both synthetic Utsira porewater and distilled deionised water. The experimental conditions chosen were between 18-80°C and 8-12 MPa (80- 120 bar), with most data generated at 37°C and 10 MPa (100 bar) – in-situ temperature and pressure at the injection point in the Utsira formation at Sleipner. Measured CO2 solubility values in distilled de-ionised water follow trends that are similar to previous studies. However, at a more detailed level, the solubility values obtained were slightly lower than data from other studies. At 37°C and 10 MPa (100 bar), measured solubility is in the order of 5.1 g of CO2 per 100 g of water. Measured CO2 solubility in synthetic Utsira porewater is broadly in line with previous studies. Solubility values are lower than those obtained for distilled de-ionised water. At 37°C and 10 MPa (100 bar), measured solubility is in the order of 4.5 g of CO2 per 100 g of solution.