Wellbore strengthening is the mechanism of increasing the fracture pressure of the rock at depth. Application of wellbore strengthening in the drilling industry enable safe drilling by preventing mud losses, drilling in narrow mud windows, accessing reserves in depleted reservoirs, and also has the potential to reduce the number of casing runs. Until now, the predominant wellbore strengthening mechanism and its occurrence in ultra-low permeability media such as shales is a subject of discussion. This dissertation presents original research that concludes that fracture tip resistance by the development of an immobile mass is the predominant wellbore strengthening mechanism for sandstone and shale formations. Wellbore strengthening in sandstones and shales was achieved with a fracture breakdown pressure increase of 65% and 30%, respectively. Oil based mud (OBM) containing in-house prepared nanoparticles (NPs) was used for hydraulic fracturing experiments performed in an experimental set-up that scaled a drilled, cased and cemented wellbore in a core. Optical microscopy, scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) analysis were performed on the cores post-testing and the fracture seal was characterized. This research demonstrated the successful application of nanoparticle-based drilling fluids in the presence of graphite in reducing mud filtration at high-pressure high-temperature (HPHT) in porous media and low-pressure low-temperature (LPLT) in filter paper. Mud filtration reductions of 76% and 100% were achieved respectively. A strong match between wellbore strengthening and mud filtration was discovered for iron-based (NP1) and calcium-based (NP2) NPs. NPs performance in virgin vs. recycled mud was quantified and the effect of NPs preparation procedure on blends performance was addressed. These results are anticipated to have a significant impact in drilling and completions operations. This dissertation was conducted by the author in a cooperative agreement between the University of Calgary and the Missouri University of Science and Technology.