The multiscale features of shale, along with the inherent presence of microporosity due to current imaging limitations, pose significant challenges in accurately describing oil transport behavior. Microscale effects, such as adsorption and slip effects, further complicate the dynamic physical processes within nanoporous shale media. In this study, we present a multiscale modeling framework for confined shale oil flow that accounts for microporosity and microscale effects, including slip effects and heterogeneity in fluid density and viscosity. Sensitivity analyses are performed to quantify the impacts of unresolved pore radius, sub-resolution porosity, slip length, and total organic carbon (TOC). Two strategies are employed to represent multiple microporosities: (1) a homogeneous microporosity weighting based on TOC, and (2) an explicitly segmented organic and inorganic microporosity. Our findings reveal that microporosity and microscale effects have a significant impact on the single-phase flow of shale oil, even if microporosity exhibits extremely low permeability. The slip effect substantially enhances the overall permeability compared to the near-wall flow effects, and the contribution of microscale effects diminishes with the increase of sub-resolution porosity and unresolved pore radius. Furthermore, this work suggests that the spatial distribution of organic and inorganic microporosities critically affects the permeability of the rock sample, particularly when the two microporosities show distinct flow mobility. This work provides a novel multiscale modeling approach that integrates unresolved pores with confinement microscale effects, offering improved predictive capability for shale oil flow. Future work should focus on extending the model to multiphase flow conditions and improving the characterization of the microporosity distributions.