Effects of Impurities in CO2 Spreading Model Development for Field Experiments in the Framework of the CO2QUEST Project

Abstract:

The aim of the CO2QUEST project (Impact of the Quality of CO₂ on Storage and Transport) is to investigate the effect of typical impurities in the CO₂ stream captured from fossil fuel power plants on its safe and economic transportation and deep geologic storage. An important part of this EU funded project is to enhance the understanding of typical impurity effects in a CO₂ stream regarding the performance of the storage. Based on the experimental site Heletz in Israel, where injection tests of water as well as of super-critical pure and impure CO₂ will be conducted, numerical simulations are performed. These studies illustrate flow and transport of CO₂ and brine as well as impurities induced chemical reactions in relation to changes in the reservoir, e.g. porosity, permeability, pH-value, and mineral composition. Using different THC codes (TOUGH2-ECO2N, TOUGHREACT, PFLOTRAN), the spatial distribution of CO₂ and impurities, both in the supercritical and aqueous phases, are calculated. The equation of state (EOS) of above numerical codes are properly modified to deal with binary/tertiary gas mixtures (e.g. CO₂-N₂ or CO₂-SO₂). In addition, simulations for a push-pull test of about 10 days duration are performed, which will be validated against experimental field data.

Preliminary results are as follows: (a) As expected, the injection of SO₂ leads to a strong decrease in pH-value, hence, the total dissolution of carbonate minerals could be observed. (b) Due to the acidic attack on clay minerals , which is enhanced compared to a pure CO₂ dissolution, a higher amount of metal ions are released, in particular Fe²⁺ and Mg²⁺ by a factor of 25 and 10, respectively. Whereas secondary precipitation occurs only for sulphur minerals, namely anhydrite and pyrite. (c) The co-injection of CO₂ with N₂ changes physical properties of the gas mixture. Increasing N₂ contents induces density decrease of the gas mixture, resulting in faster and wider plume migration compared to the pure CO₂ injection case.