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عنوان مقاله [English]
Drilling fluids have the potential for reservoir damaging, which can be investigated in laboratories. Laboratory results indicate that the permeability of fractured reservoirs decreases due to using drilling fluid in pay zones. For reducing or returning the permeability of reservoirs many additives such as sized materials can play an important role in removing an increasing permeability of damaged sections. A set of experiments was performed which clearly showed that drilling fluids could cause large irreversible damage to fractures and then could dramatically reduce the productivity of wells producing from a natural fracture network. Using sized additives in drilling fluids can significantly reduce the depth and extent of formation damage. Laboratory results showed that sized calcium carbonate (CaCO3) were less effective comparing with acid soluble fibers; therefore, they were recommended for reducing pay zoon damage in fractured reservoirs. It is worth mentioning that according to the laboratory results aggregated fibers bridge across the face of the fracture and then bentonite in drilling mud forms an effective mud cake, which finally minimizes the invasion of solids and filtration to the formation and dramatically reduces formation damage (with filtration volume of 9 ml/5hr and 50% permeability improvement).