Hydrogeochemical characteristics of deep saline aquifers in sedimentary basins in China and implications for CO2 geological storage with emphasis on total dissolved solids (TDS) and water type

The hydrogeochemistry of deep saline aquifers in sedimentary basins, in particular total dissolved solids, is one of the key criteria for CO2 storage because CO2 solubility is greatly affected by it. A detailed investigation of total dissolved solids (TDS) and water type of formation water is presented in the paper to assess the suitability of sedimentary basins in China for CO2 sequestration. Deep saline aquifers are divided into three categories based on TDS and water type: fresh-slightly saline water with TDS less than 10 g/L, semi saline-saline water with TDS ranging from 10 g/L to 50 g/L, and salty water with TDS higher than 50 g/L. The fresh, slightly saline water is dominated by water type of ClHCO3-Na in sedimentary basins in East China. Semi saline-saline and salty waters are of Cl-Na type existing in the southeast and mid-west. TDS limits are suggested for different regions of China to optimize the use of formation water. Solubility of CO2 in formation water with TDS of 1g/L approximate to 260g/L is calculated. Results show it exhibits exponential correlation to water TDS and two sharp inflections are observed at 10 g/L and 50 g/L. For fresh-slightly saline aquifer, TDS limit is defined as 3 g/L in East China while in West China, 5 g/L is suggested. For formation water with TDS of 10 g/L approximate to 150 g/L, 10 g/L is proposed for the main sedimentary basins in China. For deep saline aquifers with TDS higher than 150 g/L, CO2 storage is not suggested to avoid conflicts with salts mineral resources exploration. (c) 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.