Evaluating\nthe Impact of CO<sub>2</sub> Submersion\nTime on the Permeability and Porosity of Carbonate-Rich Geological\nSamples: A Comprehensive Laboratory Study of Middle Bakken Formation

The promising strategy of CO<sub>2</sub> capture, utilization,\nand storage (CCUS) aims to reduce CO<sub>2</sub> emissions and tackle\nthe pressing problem of global warming. Previous studies have demonstrated\nthe importance of changes in petrophysical and geomechanical characteristics\nin assessing target formations’ capacity to sequester CO<sub>2</sub>. Permeability is one of these characteristics that is essential\nto the movement of CO<sub>2</sub> inside rock formations and has a\ndirect effect on how well CO<sub>2</sub> is sequestered. Existing\nmethods calculate permeability by using effective stress, but they\nhave made unpractical assumptions that the effective stress coefficient\ncould be stable or gradually increase after CO<sub>2</sub> exposure.\nThis study addresses this research gap by presenting experiment results\non porosity, Poisson’s ratio and permeability of rock samples\nobtained from middle Bakken subjected to CO<sub>2</sub> submersion\nunder controlled confining pressure and pore pressure. Experiments\nwere conducted before and after the samples being submerged into supercritical\nCO<sub>2</sub> for durations spanning from 20 to 60 days. The results\ndemonstrated significant increases in porosity, with two samples showing\nincreases by factors of 1.5 and 2.4, respectively. Additionally, permeability\nwas observed to increase by factors ranging from 5 to 10 after submersion.\nThis research establishes empirical relationships between time, confining\npressure and pore pressure differential, and effective stress coefficient.\nThese findings provide operators with a more accurate predictive tool\nfor carbonate-rich samples in the middle Bakken formation during CO<sub>2</sub> storage. By addressing the limitations of previous methods\nand offering new insights into the behavior of rock formations under\nCO<sub>2</sub> exposure, this research enhances the evaluation of\nCO<sub>2</sub> sequestration potential.