Enforced CO2 mineralization in anhydrite-rich rocks

Carbon dioxide (CO2) emission is a major contributor to global warming and climate change. Consequently, there is an urgent need to decrease the concentration of CO2 in the atmosphere and develop reliable methods for its storage. Subsurface carbon mineralization is an effective solution to mitigate atmospheric CO2 emissions. This study is focused on investigating anhydrite-CO2-brine interactions as a means of carbon storage in anhydrite-rich reservoirs. To achieve this, we conducted experiments involving anhydrite-rich rock exposed to supercritical CO2-brine environments. Notably, we conducted a novel mineral transformation of an outcrop anhydrite-rich rock within a static reactor, replicating subsurface conditions of high temperature (333 K) and pressure (104 bar). These experiments were conducted over fifteen days, both in the absence and presence of BaCl2. A comprehensive suite of mineralogical, elemental, and geochemical analyses was employed, including X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, ion chromatographic (IC) analysis, and micro-computed tomography (micro-CT) assessments. These analyses allowed capturing the changes occurring in the rock's structure and composition due to the CO2-brine interactions. The outcomes revealed that anhydrite, when exposed to supercritical CO2-saturated brine, undergoes a significant mineral transformation. This mineral modification leads to the formation of stable minerals, including calcite, siderite, feldspar, and barite. Consequently, there was an observed increase in total carbon (TC) content of up to 177 % for the CO2-brine treatment and 266 % for the CO2-brine + BaCl2 treatment. These findings provide valuable insights into the potential of anhydrite-based CO2 storage mechanisms.