Predicting the Environmental Impact of CO<sub>2</sub> Leakage on Groundwater Quality in Onshore Regions: Integrating Geochemical Modeling with Machine Learning Approaches

A critical factor in gaining public and regulatory acceptance of carbon sequestration is the assurance that groundwater resources will be protected. Concern have been raised about the potential for CO<sub>2 </sub>to leak from abandoned oil wells and migrate into groundwater zones, posing risks to water quality such as freshwater acidification and the potential mobilization of heavy metals and other trace element through mineral dissolution. While extensive research on hydrocarbon pollution in Ogoni land abandoned oil well in Nigeria, has been conducted over decades. Studies simulating pH variation and carbonate equilibrium under CO<sub>2</sub> influence remain rare. Here, the PHREEQC geochemical modeling software was used to study carbonate equilibrium dynamics in the groundwater of the abandoned oil well sites in Ogoni land, Nigeria. Initial groundwater chemistry was simulated using baseline data from the literature, including pH, alkalinity, and major ion concentrations. The study modeled varying pH levels (5.0 to 8.5) and CO<sub>2</sub> partial pressures (10<sup>-1</sup> to 10<sup>-3</sup> atm) to evaluate changes in mineral stability, ion mobilization, and pH buffering capacity. This unbiased study analysis explored the dissolution and precipitation processes of carbonate minerals and their implications for groundwater quality in contaminated regions. Findings indicate that CO<sub>2</sub> leakage significantly lowers groundwater pH, enhances bicarbonate production, and mobilizes calcium and magnesium ions, potentially degrading water quality.