New zones in mature fields continue to be actively developed as operators strive to maintain depleting reserves. Many of the world's new reserves are discoveries made below these existing, mature reservoirs. Drilling activities in or near producing or previously abandoned reservoirs often encounter large variations in pressure gradient as depleted layers or low pressured zones are exposed during the drilling process. Zones with pressures inconsistent with the overburden are often encountered, if conventional drilling techniques are used, then the higher mud weight used to hold back the target interval may result in massive losses (lost circulation), differential sticking, sloughing, or collapsing formations in the lower-pressure zone. There is a clear advantage to drilling if we could drill by reducing the drilling window between pore pressure and fracture gradient, using cage stress (particle bridging) or wellbore strengthen (WS) to drill at higher mud weights without losing fluid. This work presents the approach of WS that can be accomplished with treatment of the whole drilling fluid with Lost Preventive material (LPM) that are designed to seal and effectively increase fracture resistance allowing the operator to drill through a weak formation zone successfully with minimal to zero losses. Other models and materials were also investigated to determine their suitability and operational design parameters. Models for LPM application procedure (minimum volumetric requirements, quantitative requirements for filter cake thickness and optimise hydraulic parameters for effective cake deposition) were developed. The advantage of this process is reduction in drilling difficulties and non productive time for operators. Some experimental work was also carried out to determine the port throat of the formation, particle size distribution (PSD), strength & stability of the LPM filter cake, as well as the compatibility of different LPMs with different mud system. Results from case studies were also presented which shows tremendous result in reduction of NPTs via no loss circulation.