Multi-scale fractures are developed in tight and low-permeability sandstone reservoirs,and this paper discussed the characterization methods of multi-scale natural fractures in tight and low-permeability sandstone reservoirs.Methods:According to natural fractures sizes and mechanical stratigraphy interfaces,which constrain natural fracture propagation,natural fractures are divided into four scales.According to outcrops,cores,well logs,three dimensional (3D) seismic data and micro- analysis data,the characterization methods of multi-scale natural fractures were studied based on the characteristics of multi-scale natural fractures and the accuracy of different data.Finally,the multi-scale fracture characterization methods proposed in this paper were used to characterize the multi-scale fractures in the tight sandstone reservoirs in the southwestern Ordos Basin to test the methods.Results: Natural fractures are divided into micro-scale,small-scale,meso-scale and macro-scale ones in tight and low-permeability sandstone reservoirs.The fractures at different scales show different characteristics.Macro- scale fractures are mainly characterized by post-stack attributes of 3D seismic data.Meso-scale and small-scale fractures can be described in single wells by combining cores,image logs and conventional logs,and they can be comprehensively predicted and evaluated by pre-stack anisotropy of 3D seismic data and reservoir geomechanics method in combination with cores,image logs and conventional logs.Micro-scale fractures are generally characterized by micro-scale analysis method,such as thin sections, scanning electron microscope,computerized tomography (CT) scanning etc.And micro-scale fractures can be predicted under the control of the controlling factors of micro-scale fractures.Conclusions:The multi-scale fracture characterization methods proposed in this paper can provide reference for the characterization of the multi-scale fractures in other tight and low-permeability sandstone reservoirs.