Alshammari et al. (2025): CO₂ Mineralization in Produced Water: Transforming Waste Brines into a Carbon Sink
Salem Alshammari, Hussain Saleem, Dong Kyu, IN: Society of Petroleum Engineers Middle East Oil & Gas Show, https://doi.org/10.2118/227029-MS
Produced brines from oil and gas fields are rich in divalent cations, offering the potential for CO₂ sequestration as thermodynamically stable carbonates. This study investigates CO₂ mineralization in produced water through yard testing the brine alkalization process in a continuously stirred tank reactor (CSTR) having a capacity of 600 L to demonstrate the kinetics and thermodynamics of magnesium and calcium hydroxide mineral precipitation at different pH regimes. Analytical characterization of the brine chemistry was done using ion chromatography (IC), inductively coupled plasma-atomic absorption spectroscopy (ICP-AES) and pH measurements. The results from the yard test demonstrate the selective removal of magnesium hydroxide after the initial alkalization step with a pH value between 8 to 9 followed by calcium hydroxide formation after the complete removal of magnesium at a pH above 10. A holistic understanding of the effect of process parameters like temperature, pressure, solid-to-liquid ratio, and the aqueous medium ionic strength is crucial for the rational design of large-scale ex-situ CO₂ mineralization processes. Therefore, the authors investigated various parameters affecting the carbonation of the extracted calcium hydroxide minerals from the alkalization process using chemical thermodynamic modeling. The models were based on Pitzer’s equations to account for the deviation from ideality in the electrolyte solution and compute the activities of its components whereas the gas phase fugacity was modeled using the Peng-Robenson (PR) equation of state. Increasing the temperature and reducing the pressure enhanced the CO₂ mineralization thermodynamic yield. They also studied the stepwise addition of CO₂ in a system of calcium hydroxide in water until a certain fugacity is reached (e.g., 1 atm). This simulates scenarios where CO₂ mass transfer or the hydration/hydroxylation of CO₂ is limiting.