Unconventional oil reservoirs have great potential to become significant sources of petroleum production in the future. Many shale oil systems consist of nanoscale pores and fractures that are significantly smaller than those from conventional reservoirs, and pore sizes are only slightly more than one order of magnitude of those of the saturating fluid molecules. This difference will cause abnormal wettability effect and typical fluid flow mechanisms in unconventional oil systems. Therefore, it is increasingly important to investigate fluid flow behaviours in nanoscale porous media. In this work, a lab-on-chip approach for the direct visualization of the water—oil flow in nanoscale channels was developed by using an advanced laser microscopy system combined with a nanofluidic chip. For the micro-scale study of interface transmission during the drainage and imbibition processes, parallel linear nanofluidic chips were used. A comprehensive study of water—oil flow behaviours is presented. During the drainage process, liquids tend to have a piston-like flow in nanoscale channels; both residual phase saturation and configuration affect the flow behaviour on such small scale; during the imbibition process, a fading-out phenomenon was observed. For a macroscale study of pressure and recovery relationships, unusual entrance pressure was discovered by using network nanofluidic chips comparing to conventional results.