Assessing roles of geochemical reactions on CO2 plume, injectivity and residual trapping

Abstract

With increasing CO2 concentration in the atmosphere, CO2 geo-aequestration has become a popular technique to counter the dangers of global warming resulting from high levels of CO2 in the atmosphere. This paper examins sequestration parameters such as CO2 plume behaviour, residual gas trapping and injectivity as a means of achieving safe and successful CO2 storage in saline aquifers. Mineral precipitation/dissolution rates are used to establish a relationship between these parameters and geochemical reactions in saline aquifers. To achieve this, mechanistic models (6 models with different inputs, created using CMG – GEM, 2016 and WINPROP, 2016) are simulated using input data from literature and studying changes in fluids and formation properties as well as mineral precipitation/dissolution rates in aquifers when subjected to different conditions in the different models.The results from the models show that high CO2 dissolution, which creates large CO2 plume, leads to high mineral dissolution/precipitation as results of increased fluid-rock interactions (geochemical reactions); whereas injectivity, although enhanced by CO2-water cyclic injection, does not show much increase in bottom hole pressure when mineral trapping (thus geochemical reactions) is introduced into the model. Sensitivity study on residual gas trapping shows that high residual gas saturation leads to reduced mineral precipitation/dissolution due to the reduced amount of dissolved CO2 in brine. Also, rapid changes in the bottom hole pressure at high residual gas saturation means that a formation that fosters high residual gas trapping, rather than CO2 dissolution in brine, is more likely to experience injectivity issues during the sequestration process.

Keywords

• Geochemical reactions
• CO2 plume
• Residual (gas) trapping
• Injectivity
• Mineral precipitation
• Mineral dissolution