Enhancing CO₂ Sequestration in Deep and Highly Saline Aquifers Using Chelating Agents

Deep saline aquifers are a critical target for large-scale CO₂ sequestration due to their widespread distribution, huge pore volume, and favorable geochemical properties. However, one of the key challenges in these aquifers is the lower CO₂ solubility and storage capacity caused by cations such as calcium and magnesium, which contribute to salt precipitation and pore blockage during CO₂ injection. This study investigates the use of chelating agents such as ethylenediaminetetraacetic acid (EDTA) and N, N-dicarboxymethyl glutamic acid (GLDA), as reservoir conditioners that selectively bind these cations, thereby preventing salt precipitation and enhancing CO₂ solubility in brine. The research employs a combination of solubility tests and core flooding experiments to simulate aquifer conditions. Solubility tests were conducted under high-pressure, high-temperature conditions representative of deep aquifer environments in a pressure-volume-temperature (PVT) system, using synthetic brine/seawater formulations treated with varying concentrations of EDTA and GLDA. These tests assess the agents' effectiveness in sequestering targeted cations and increasing CO₂ dissolution. Complementary analytical techniques, such as inductively coupled plasma (ICP) spectroscopy, assisted in quantifying dissolved cation concentrations. The results showed that pH and salinity play critical roles in the solubilization of CO₂ in brine. Both GLDA and EDTA performed on par; however, GLDA was able to chelate slightly more ions and promote solubility. Furthermore, core flooding experiments will be carried out using carbonate-rich rock samples to evaluate the impact of chelating agents on CO₂ injectivity, mineral-fluid interactions, and pore structure evolution. These dynamic tests assess the performance of these chelating agents towards improving aquifer storage capacity in flow conditions. X-ray computed tomography (CT) will be used to visualize changes in pore structure and mineral distribution, sonic velocity measurements for tracking changes in the mechanical properties of rock samples, and low-field nuclear magnetic resonance (NMR) for evaluating pore size profile evolution. This novel approach acknowledges the environmental concerns of chelating agent degradation in aquifer conditions, as well as the cost-effectiveness of the squeeze treatment to enhance the CO₂ storage through chelation in a highly saline formation, ensuring a sustainable and promising technique for global CO₂ reduction.