الملخص الإنجليزي
CO2 injection into saline aquifers as part of the CCS process induces chemical processes represented with CO2 dissolution into water and minerals reactions which can disturb the brine equilibrium and change the aquifer’s petrophysical properties. This thesis aimed to implement numerical tools for assessing the interactions between carbon dioxide, the original brine, and the aquifer minerals with more focus on exploring the parameters that could optimize the amount of solubility and mineral trapping. The study was conducted on the Dogger carbonate aquifer in the Paris Basin.
Modelling was performed using PHREEQC and CMG-GEM. PHREEQC assessed geochemical reactions of injecting CO2 at a fixed partial pressure into the aquifer, evaluating the effects of pressure, temperature, pH, solution ions, and mineralogy on geochemical trapping. The study split the evaluation into two parts to analyze each mechanism separately. CMG-GEM was utilized for 2D reactive transport simulations to study the impact of physical and chemical trapping mechanisms, as well as assessing compatibility with PHREEQC.
The results revealed that the abundance of sodium relative to calcium and magnesium in the solution could increase CO2 solubility and system pH. For mineral reactions, equilibrium modelling and semi-kinetic simulations indicated that silicate mineral reaction rates might be overestimated compared to fully kinetic modelling. In the base case, albite dissolution formed dawsonite, with other carbonate minerals contributing minimally. Sensitivity analysis indicated that higher pressures and temperatures improved mineral trapping efficiency, with pressure significantly affecting dawsonite precipitation rates. Albite contributed positively to mineral trapping with higher volume fractions, while illite had an opposing effect despite being a silicate. Increased calcite volume slowed mineral reaction rates, improving pH equilibrium and reducing porosity loss, though mineral trapping declined. Primary carbonate minerals were crucial for initial positive mineral trapping. Minerals did not influence solubility trapping.
Reactive transport simulations confirmed the compatibility of GEM geochemistry with PHREEQC. However, mineral trapping contributed only about 1% to overall trapping after a millennium. RTM findings suggested faster carbonate precipitation with CO2-rich brine than with supercritical CO2. In conclusion, carbonate formations offer advantages for pH buffering and minimal storage impact, with specific cation-rich minerals significantly enhancing mineral trapping significantly.
