Application of nano or biomaterials for enhanced oil recovery (EOR) has been recently much attended by petroleum engineering researchers. However, how would be the displacement mechanisms and how would change the recovery efficiency while nano and biomaterials are used simultaneously is still an open question. To this end, a series of injection tests performed on micromodel containing shale strikes. Three types of biomaterials including biosurfactant, bioemulsifier, and biopolymer beside two types of nanoparticles including SiO2 and TiO2 at different concentrations were used as injection fluids. The microscopic as well as macroscopic efficiency of displacements were observed from analysis of images recorded during the tests. Microscopic observations revealed different mechanisms responsible for oil recovery including: wettability alteration, thinning oil film, interfacial tension (IFT) reduction, and water in oil emulsion formation. Contact angle experiments showed changes in the surface wetness from an oil-wet to neutral-wet/water-wet conditions when a layer of nano-biomaterial covered thin sections of a shaly sandstone. Also the results showed that the presence of shales causes early breakthrough and ultimate oil recovery reduction. Shales act as flow barriers and enhance injection fluid viscous fingering. Displacement efficiency in shaly systems is sharply related to the shale distribution. Oil recovery after breakthrough in shaly systems is progressive and considerable volume of oil in place is recovered after breakthrough. The highest efficiency, 78%, observed while injecting one pore volume of biopolymer and SiO2 nanoparticles. This work illustrates for the first time the mechanisms involved in nano-biomaterial-crude oil displacements.