We study pore-scale rheological phenomena in two-dimensional sheared wet granular materials. Simulations use a coupled cascaded lattice Boltzmann and discrete element method (LB-DEM), to model the liquid-gas multiphase flows and multiple-solid-particle dynamics, respectively. In the coupled LB-DEM model the liquid-gas two-phase flow is solved by the pseudopotential LBM, and the cascaded collision operator is used to enhance numerical performance. The flow of the granular material, composed of solid grains, is solved by the classical DEM resorting to fictitious overlaps between the grains. The two solvers are fully two-way coupled: the movement of solid particles leads to disappearances and births of fluid points and the solid particle dynamics are affected by particle-particle and fluid-solid interactions, including hydrodynamic momentum exchange and capillary forces. The model has been well validated based on various benchmarks. In this study, the wet granular material is prepared by first filling a rectangular domain with solid particles and then partially filling the pores between the particles with the liquid phase. The material is then sheared based on the standard Couette flow configuration. The simulations show that the apparent viscosity of the system attains a minimum when the material is wet but not fully saturated, i.e., at a saturation of 10%. Such an observation is coherent both for materials composed of monodisperse and polydisperse particles. The underlying mechanism is elucidated based on the pore-scale study of liquid patch dynamics. It is shown that, with increasing liquid saturation, the rheology of the wet granular materials is affected by two competing effects: a larger number of liquid patches leads to a fluidization of the system, while larger liquid patches aggregating the particles by capillary forces may hinder particle flow.