In this research, permeability impairment caused by drilling fluids and subsequent cleaning and permeability enhancement by back-flow were investigated by means of experimental and simulation studies. Permeability damage caused by three different drilling fluids was measured experimentally by core tests as a function of the filtration pressure and analyzed using a simulator describing the fines migration and retention in porous media. The pore throat plugging criteria for the three drilling fluids were determined. The particle concentration and the fraction of depositing particles were obtained simultaneously as a function of time and distance along the core length by numerical solution. Simulations were run both with experimental data in forward and backward directions along the core samples. Permeability damage ratio was correlated with respect to drilling filtration pressure specially for each type of the drilling fluids and type curves were constructed. Simulation results accurately match the experimental data, indicating that this simulator can be used for the estimation of permeability reduction, and the permeability and porosity variation along the core samples at various filtration pressures. X-Ray digital image subtraction was applied to different sections of the core plugs before and after the circulation to visualize the fines migration into porous media. The maximum damage ratio was obtained with the CMC added drilling fluid with 81%. In the absence of CMC and Polymer-XT, the damage ratio was found as 72.8%. It was also determined that a polymer-added drilling fluid characterized with 63.8% permeability damage ratio is the optimum drilling fluid, causing less formation damage than the water-based bentonite mud

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