Experimental study of CO2 flow behavior and storage potential within low porosity and permeability aquifer

Current research on CO2 storage in aquifers typically focuses on high porosity and permeability formations to maximize storage capacity, often overlooking crucial factors such as long-term stability and safety. To address this gap, this study explores the potential for CO2 storage in low porosity and permeability aquifers, utilizing core samples from Ordos storage pilot site. The corresponding T2 spectra exhibit characteristic of high-left and lowright peaks, which separately influence storage capacity and flow behavior. Critical porosity and permeability thresholds were identified, distinguishing the contributions of different pores to storage efficiency. Lower temperature, higher pressure, and supercritical state extend the effective gas displacement duration, enhancing contribution of small pores to CO2 storage. CO2-water redistribution within varying pore sizes leads to the synchronous behavior between injection pressure and water saturation, helping to alleviate CO2 injection challenges. As permeability decreases and displacement cycle increases, relative permeability curves display rightward and leftward shifts, respectively. While these shifts reduce movable pore space and CO2 storage capacity, they concurrently increase residual gas and connate water saturations, thus enhancing CO2 storage stability through residual gas trapping and solubility trapping mechanisms. Nanopore CO2 adsorption further strengthens this storage stability. Low permeability aquifers, characterized by tighter grain packing, stronger cementation, and smaller pores, provide superior resistance to geochemical dissolution and mechanical damage. Consequently, these aquifers provide unique advantages in structural stability and long-term sequestration safety compared to higher permeability counterparts. Furthermore, the greater abundance of low permeability aquifers may compensate for their disadvantage of low storage efficiency.