Accelerating mineral carbonation in hydraulic fracturing flowback and produced water using CO2-rich gas

Abstract

Mineral carbonation is a Carbon Capture Utilization and Storage (CCUS) technique that can be used to remove or divert carbon dioxide (CO2) from the atmosphere and store it in carbonate minerals. Hydraulic fracturing flowback and produced water (FPW) is Ca- and Mg-rich wastewater generated by the petroleum industry that can be used to sequester CO2 in benign minerals. Here, we describe the rate and efficiency of mineral carbonation achieved by sparging 10% CO2/90% N2 gas into pH-adjusted FPW, collected from the Duvernay Formation in the Western Canadian Sedimentary Basin. Our results indicate that calcite (CaCO3) precipitated at the expense of brucite [Mg(OH)2] dissolution following CO2 injection; as such, no Mg-carbonate precipitates were formed. The carbonation reaction reached steady state within 1 h and 14.2% of the aqueous Ca in the FPW was precipitated as calcite, sequestering 1.56 ± 0.33 g CO2 L−1 of FPW. Our dissolved inorganic carbon measurements, geochemical models, and stable carbon isotope results indicate that CO2 mineralization can be maximized by maintaining solution at pH ≥ 10 during CO2 sparging. If all of the Ca and Mg in the FPW could be carbonated, it would offer a greater CO2 sequestration potential of 12.5 ± 0.3 g CO2 L−1.