Abstract: Fracturing stimulation is the main method for development of tight oil.It can improve reservoir quality,but also can cause damages to reservoirs.Taking the Chang 7 Member of Yanchang Formation in Ordos Basin as an example,the relationship between the characteristics of tight oil reservoirs and fracturing fluid damage is studied based on experimental analysis,such as physical properties of reservoir,casting thin sections,scanning electron microscope(SEM),X-ray diffraction(XRD),rate-controlled mercury penetration,NMR,CT and sensitivity test.The Chang 7 Member is a typical tight oil reservoir in which the content of interstitial materials is as high as 15%.Illite,which is easy to transport and expand,accounts for a large proportion in the interstitial materials; Both pores and pore throats are of micro-nanometer scale,and the pore throats have poor connectivity.Large pores are generally controlled by small throats.The tight oil reservoir of the Chang 7 Member has moderate to weak velocity sensitivity(the damage rate of core permeability is in the range of 0.33-0.48),strong water sensitivity(the damage rate of core permeability is 0.14-0.28),and strong tendency of water blocking.Therefore,clay inhibitors,anti-swelling agents and cleanup additives should be added to the fracturing fluid formula to reduce the damage of fracturing fluid to the reservoir;salt sensitivity damage would occur when the salinity of the fracturing fluid running into the well is lower than 10,000 mg/L;the particle size of the fracturing fluid residue is 2.25-8.39 μm.For tight oil reservoirs,various damages such as filter cakes,sediments,absorption blocking and bridge plug can occur.It is considered through integrated study that using low damage fracturing fluids is the main way to reduce the residual damage.

Key words: sensibility, fracturing fluid, reservoir, tight oil, Yanchang Formation, Triassic, Ordos Basin