Varieties of pore‐scale numerical and empirical approaches have been proposed to predict the rock permeability when the pore structure is known, for example, microscopic computerized tomography (micro‐CT) technology. A comparative study on these approaches is conducted in this paper. A reference dataset of nine micro‐CT images of porous rocks is generated and processed including artificial sandpacks, tight sandstone, and carbonate. Multiple numerical and empirical approaches are used to compute the absolute permeability of micro‐CT images including the image voxel‐based solver (VBS), pore network model (PNM), Lattice Boltzmann method (LBM), Kozeny‐Carman (K‐C) equation, and Thomeer relation. Computational accuracy and efficiency of different numerical approaches are investigated. The results indicate that good agreements among numerical solvers are achieved for the sample with a homogeneous structure, while the disagreement increases with an increase in heterogeneity and complexity of pore structure. The LBM and VBS solver both have a relative higher computation accuracy, whereas the PNM solver is less accurate due to simplification on the topological structure. The computation efficiency of the different solver is generally computation resources dependent, and the PNM solver is the fastest, followed by VBS and LBM solver. As expected, empirical relation can over‐estimate permeability by a magnification of 50 or more, particularly for those strong heterogeneous structures reported in this study. Nevertheless, empirical relation is still applicable for artificial rocks.

The pore‐scale imbibition mechanism in fractured water‐wetted reservoirs has been acknowledged as an efficient tool to enhance oil recovery. Most rock in a natural reservoir is mixed‐wetted, but most studies on the pore‐scale imbibition process only focused on the water‐wetted rock. This paper adopts two mixed‐wetted core samples for microspontaneous imbibition experiment, micro‐CT scanning, and nuclear magnetic resonance (NMR) test. The results indicate that the pore radius distribution of the segmented CT images is consistent with that of the NMR test. The microimbibition recovery ratio of core No. 34‐1 and core No. 64 in the spontaneous imbibition experiment are 27.7% and 58.2%, which agrees well with that computed by the micro‐CT scanning image (27.63% and 56.09%). Based on the segmented images, the influences of the Jamin's effect, pore size distribution, and wettability on the microspontaneous imbibition are visualized and quantitatively studied. The Jamin's effect is the important factor that hinders the microimbibition process. The main pore size of imbibition distributes in the range of 1‐25 μm. Furthermore, the pore‐scale spontaneous imbibition process in a single pore with mixed wettability is investigated and analyzed. The relationships among the contact angle, capillary force, recovery ratio, wettability, and the microimbibition recovery are revealed.