Experimental investigation of thermophysical properties in CO2-saturated Brine under variable temperatures (303 to 333 K), pressures (0.1 to 30 MPa), and salt types and concentrations

Abstract This study focuses on investigating the thermophysical properties of brines under conditions associated with geothermal energy extraction and enhanced geothermal systems (EGS), particularly examining parameters such as density, viscosity, and pH. The impact of CO 2 saturation on these properties was analysed at pressures of up to 30 MPa in a range of temperatures between 303 and 333 K. This research targets low to medium enthalpy geothermal systems in regions with lower thermal gradients, such as the northern German basin. This focus elucidates the behaviour of geothermal systems under medium temperatures and elevated pressure conditions. These conditions are also relevant to carbon dioxide sequestration in saline aquifers. A range of sodium chloride (NaCl) brine concentrations of up to 4.28 mol kg − 1 , and mixtures of 85:15 NaCl: CaCl 2 were investigated in order to assess the effect of salt type and concentration on the density and viscosity. Additionally, solutions were prepared being saturated with carbon dioxide (CO 2 ) to assess the influence of varying salt concentrations and pressure on the pH, highlighting that dissolved CO 2 primarily governs pH by forming carbonic acid, with salt concentration and pressure having a secondary influence, which is relevant to the choice of materials used in the geothermal plant.