Secondary and tertiary recovery processes can lead to severe and permenant reductions in permeability because of interactions between injected fluids and the reservoir rock. Permeability damage was suspected as a factor contributing to post completion production declines observed during waterflooding of an unconsolidated limestone. This study summarizes the laboratory studies undertaken to evaluate and understand permeability damage in limestone reservoirs. The influence of brine composition, salinity of alkaline fluid and injection rate on permeability damage were evaluated in consolidated and unconsolidated cores. Effluent pH and Cl concentrations were measured at the outlet of the porous medium. Brines were prepared with sodium, calcium and potassium salts (NaCl, CaCl 2, KCl). High pH values in produced water caused the permeability reduction and consequently the pores were plugged and formation damage was observed. In alkaline flooding experiments, permeability reduction was observed as a result of high pH alkaline fluids (NaOH, NaSiO 4). The permeability reduction was decreased using NaCl, CaCl 2 and KCl mixtures and high oil recoveries were obtained. Suspended solid particles were released and moved with injection water as a result of Cl concentration below the critical salt concentration caused the permeability reduction and the formation damage was occurred.