1�� SinoPEC Exploration �� Production ��esearch Institute��Beijing 100083��China; 2�� SinoPEC Key Laboratory of Shale Oil/Gas Exploration and Production Technology��Beijing 100083��China; 3�� National Key Laboratory of Corporation of Shale Oil/Gas Enrichment Mechanism and Effective Development��SinoPEC�� Beijing 100083��China; 4�� College of Geo- Exploration Science and Technology��Jilin University��Changchun 130026��China

The presence of horizontal fractures enhances seismic anisotropy of shales�� Calculation based on the effective medium theory indicates that horizontal fractures have little effects on velocities along the direction pa- rallel to fractures�� but can significantly reduce velocities along the direction normal to fractures�� Seismic respon- ses of shales with horizontal fractures are calculated based on the reflector model and the anisotropic propagator matrix method��in which the reflections are a combination of the contrast in impedance due to the variations in fracture density��anisotropic propagation of waves within the shales��and the tuning and interferences associated with layer thickness�� Calculated results indicate that seismic reflections are sensitive to reservoir layer thickness and fracture density�� Anisotropic propagation alters amplitudes and phases of reflections�� It corresponds to high- er reflection amplitudes for the case of surrounding sandstone with higher velocity because the increase in frac- ture density increases the contrast in impedance between the shale and sandstone�� In contrast��the surrounding sandstone with lower velocity corresponds to lower reflection amplitudes for the increase in fracture density��