Impact of petrophysical properties on CO₂ residual trapping in limestone formations

CO₂ residual trapping, one of the key trapping mechanisms, is controlled by several factors, including pore structure and permeability. However, there is a lack of investigation of CO₂ residual trapping, particularly for limestone formations, as a function of their petrophysical characteristics. Thus, here limestone samples of different permeability ranges i.e., low (1–10 mD), medium (20–60 mD), and high (> 60 mD) permeability, were selected. The samples were first fully characterized using SEM, NMR, XRD, and capillary pressure measurement to evaluate the pore structure and sizes. A series of core flooding experiments were carried out at supercritical conditions (P = 10 MPa and T = 323 K) including 1) drainage process to determine the initial saturation of CO₂ (S_gi), and 2) imbibition process to determine the residual CO₂ saturation (S_gr). Results indicate that CO₂ stored by residual trapping is highly dependent on the rock properties and associated pore network. Our observations suggest that no proper correlation exists between S_gi and S_gr when permeability increases. Medium permeability rocks depicted the largest CO₂ saturation of 33 %. While the trapping efficiency (S_gr/S_gi) was found to decrease monotonically from 60.7 % to 21.7 % with increasing permeability (5 mD to 680 mD), low permeability rocks will depict relatively poor injectivity. Moreover, the results obtained were modeled using Land and Spiteri trapping models, and our data perfectly fits the two models. This study extensively investigates residual trapping efficiency affected by rock properties in limestone reservoirs. Additionally, it provides better insights into residual trapping pertinent to CO₂ storage.