Wettability is an important factor controlling the pore-filling mechanism and displacement efficiency in the subsurface pore space. The trapped phase can be mobilized by wettability alteration, which is one of the main mechanisms of enhanced oil recovery technologies, such as surfactant flooding and low-salinity waterflooding (LSWF). Despite recent advances in the simulation of wettability alteration at the core-scale or beyond, there are very few works that have modeled the wettability alteration at the pore-scale, especially on three-dimensional (3D) micro-CT images, causing fluid displacement and retrapping mechanisms during wettability alteration in real porous media are not well understood. With this objective, a wettability alteration model by low-salinity is developed and implemented in the open-source computational fluid dynamics software OpenFOAM (Open Source Field Operation and Manipulation). This study takes into account the effect of different degrees of wettability alteration, different time scales of wettability alteration, and different injection scenarios on trapped oil mobilization and the ultimate oil recovery factor. A larger degree of wettability alteration results in a higher oil recovery factor during tertiary LSWF. However, the oil recovery factor decreases with the increase of wettability alteration degree due to the snap-off effect during secondary LSWF. During tertiary LSWF, a lower wettability alteration time scale under the same degree of wettability alteration produces more oil. This study emphasizes the important interplay between wettability alteration, pore structure, and time scale during LSWF, and can explain some observations in micro-CT experiments.