Experimental Study on the Loss of Pore Water in Geological CO2 Storage Reservoirs and Analysis of Storage Characteristics

To investigate the coupling relationship between reservoir CO ₂ storage capacity and pore water loss, this study employed cyclic drying experiments to collect T ₂ spectrum data from sandstone at saturation and after 1–15 drying cycles. Based on this data, pore water loss characteristics were analyzed, delineating the T ₂ values and pore size ranges corresponding to film water, capillary water, and free water. Focusing on the single-cycle loss rate of each pore water type relative to its initial content, a significant coupling relationship was observed between capillary water and free water loss rates. Specifically: Capillary water loss initially increases then decreases with drying cycles, exhibiting a parabolic pattern and peaking between the 5th and 7th cycles; The free water loss rate rapidly decreased to 14.81% of its original content, after which the loss rate remained below 3% of the original content. The film water loss rate exhibited more discrete variations, with some specimens showing an increase in content during the second drying cycle. This study established a pore water loss migration model and an ideal capillary model. By fitting the pore water loss rate formula within capillaries and deriving the reservoir capillary force variation formula based on the Young-Laplace equation, it provides a novel evaluation strategy for assessing CO ₂ sequestration effectiveness from the perspective of reservoir pore water saturation for geological CO ₂ storage technology.