Calcium sulfate deposition damages the reservoir formation. It is usually formed due to the brine thermodynamic equilibrium disturbance. Injection and formation waters are rich in sulfate (4224 mg/L) and calcium (21,240 mg/L), respectively. Then water injection into sandstone reservoirs is commonly associated with the calcium sulfate deposition due to the mixing of incompatible waters. DETPMP (diethylenetriamine penta methylene phosphonic acid) inhibitors are employed to inhibit calcium sulfate deposition. For this purpose, compatibility test in sandstone core samples with porosity from 10-20% and permeability of around 40 md was performed at different injection rates (as reference test). Then the injection water with different concentration of scale inhibitor from 10-75 mg/L was injected into sandstone core saturated with formation water (as an inhibition test). The corresponding comparison of results shows damage ratios of 0.67-0.78 and 0.68-1.00 for compatibility and inhibition tests, respectively. DETPMP minimum concentration to prevent calcium sulfate precipitation was 75 mg/L. The profile change of scale deposition is much more important than decrease in amount of scale deposition. The inhibitors not only reduce the amount of deposition but also its profile. A kinetic-mass transfer model was developed to model the distribution of species in inhibition and compatibility tests. Then the permeability reduction in compatibility test and inhibition test were modeled. The absolute average deviations for calculation of permeability reduction ratio in compatibility and inhibition test were 3.94 and 4.34% respectively.