Reactive Transport Modelling of CO₂ Injection Into High CO₂ Field

Gas reservoirs often contain a proportion amount of naturally occurring CO₂, ranging from a few percent up to 70% by volume. A carbonate gas field located in offshore Sarawak, eastern Malaysia has a very high concentration of CO₂ and expected to be a world pioneer offshore CO₂ storage in high CO₂ field with the accumulated amount of 70 % mole of the gas in place. Carbon dioxide from the gas field is removed from the gas production stream in a central gas processing facility and then the CO₂ is compressed, transported and stored underground in the carbonate reef reservoir of the same gas field. This study details the geochemical effects of CO₂ injection into the field as part of the proposed field development. In this study, we ran a two-dimensional reactive transport models using TOUGHREACT. The model was run for 300 years at the temperature of 140°C and pressure of 352 bars. The CO₂ was injected for 30 years below gas water contact (GWC) in the aquifer. The modelling results shows that the overall geochemical alterations of injected CO₂ into solid phase are minimal and is confined to the region below the original gas water contact with the minimal additional impact on injectivity. This is due to the dry-out formation vicinity to the injection well that lead to the small amount of salt precipitation. These findings demonstrate the importance of geochemical reactions study when injecting CO₂ into high CO₂ gas field at high pressure and temperature.