Abstract: Experiments are conducted on the damage mechanism of fracturing fluids by using the real sandstone model to identify the reservoir damage factors caused by fracturing fluids, to optimize fracturing fluid system, and reduce or even eliminate the damage with the most effective method. What's more, the micro-mechanism of reservoir damage caused by fracturing fluids is analyzed on the basis of analyzing the reservoir geological characteristics, fluid properties, and reservoir sensitivity. Experimental results show that the rate of water-block damage caused by fracturing fluids is 46.6%, the rates of reservoir damage and fracture damage caused by residue due to the low reservoir pressure coefficient and fracturing fluids are 25.7% and 60% respectively. Rock wettability is altered by selecting out suitable surfactant so as to reduce the waterblock damage caused by fracturing fluids. The reservoir damage caused by fracturing fluid residue is reduced by developing the fracturing fluid system with low residue so as to improve the permeable capability of seepage flow from reservoirs to fractures. All of this provides theoretical support for the development of novel low-damage fracturing fluid systems and relevant technologies suitable to low permeability oilfields.

Key words: fracturing fluid, micro-mechanism, sandstone model, damage, wettability, Xifeng Oilfield, Ordos Basin