Sensitivities of injection rates for single well CO2 injection into saline aquifers

This paper investigates methods to predict potential injection rates of CO2 into a saline aquifer and analyses the sensitivities of the input parameters. Geological parameters are based on conditions at the European CO2 Onshore Research Storage and Verification Project in Ketzin, Germany, and varied within an acceptable range. Two injection regimes for CO2 are analysed: pressure controlled injection and power plant controlled injection, where the CO2 flux depends on the load curve of a 600 MWnet lignite power plant. The results are determined with a numerical model and compared to an analytical solution with constant pressure injection. The injection rates depend mainly on the geological setting and only slightly on technical parameters. Aquifer permeability and thickness show approximately linear sensitivity and have a dominant impact. Depth is also of high importance, but the impact is more complex and is based on geothermal temperature and hydrostatic gradient, which affect viscosity, compressibility and caprock stability. Vertical anisotropy is insensitive. The difference in the mean rate between constant pressure injection and power plant controlled injection is 8%. Peak injection rates are 29% above mean injection rates, which shows that the reservoir can effectively dampen rate variations. The analytical solution predicts the highest injection rates, the lowest temporal variability and decreasing rates with injection duration. The numerical solution predicts a stronger temporal variability and the rates increase with duration. In the initial phase the differences between the methods add up to a factor of 1.45.