Artificially induced flowing channels called hydraulic fractures are created inside the reservoir, to access virgin formation with low reservoir quality, partially drained sections, to bypass the damaged area around the wellbore, establish better reservoir exposure and to decrease the drawdown pressure. The physical placement of the fracture treatment can be a challenge in wells containing multiple reservoir layers with various geological properties or massive potential pay intervals as well as depleted zones. The placement of the hydraulic fracture treatment in this regards is often carried out by pumping multiple fracture treatments in stages. Diverting agents come into play mainly in 2 different situations as follows: when there is no possibility to mechanically isolate the given well section or when is intended to increase fracture complexity (prevent growing only in one direction, create branches, etc.). In this case, particulate materials can be used to bridge the face of the wellbore section, or the initially induced fractures, thus diverting treatment fluids to another section of the open hole or divert fracture growing by subsequent increase in hydraulic fracture pressure. Developments in non-damaging and self-degrading diverting agents with high plugging efficiency create new possibilities for re-fracturing operations, by temporary sealing the existing fractures and forcing the stimulation fluid towards unstimulated formation areas. Parameters such as size, shape, chemical composition and diverting material concentration dictate further achievements such as creation of complex fracture networks in low permeable layers, fracture communication inhibition between hydraulically stimulated wellbores and reduction of mechanical isolation equipment, which often are prone to failure. Field diagnostics are used to assess diverting performance in multi-stage fractured wells. For near-wellbore applications, monitoring technologies such as radioactive tracers or distributed temperature and acoustic sensing is to determine treatment fluid placement. Downhole microseismic monitoring could be used for far-field indication of diversion success in wells with multiple intervals. The objective of the thesis is to analyse different isolation methods for multi-stage fracturing operations used in horizontal wellbores together with in depth analysis on diverting material solution , to assess practical results (i.e. dissolution test) and provide continuous technic and economic improvement. The results of this study should provide a clear overview of the isolation process and its techniques and the various influencing factors, which exist in the Brown Field environments from Romania.