Abstract: Water sensitivity damage mechanism is investigated to accurately assess damage from fracturing fluid to low permeability gas reservoirs.Based on results of X-ray diffraction,scanning electron microscopy and core flow test results,nuclear magnetic resonance(NMR)technique was employed in the experiment to evaluate water sensitivity damage caused by guar gum fracturing fluid and acidic fracturing fluid.The results show that the average water sensitivity damage caused by the two fracturing fluids is 12.68% and 12.77%,respectively.The degree of sensitivity damage depends on the content of illite/smectite mixed layer or absolute illite content and total clay content,but has little relation to the type of fracturing fluid.There is a certain relationship between water sensitivity damage and flow back degree.The damage rate showed a rising tendency when the flow back volume is 0-2 times that of pore volume,and the damage rate was primarily stable when the flow back volume is 2-10 times that of pore volume.Water sensitivity experimental results of different types of pores and different fracturing fluids show different nuclear magnetic resonance(NMR)features.Through this study,a new qualitative approach to evaluate water sensitivity damage from fracturing fluids is proposed.