Normal reflection from a fractured reservoir is analyzed using frequency-dependent seismic attributes. Processing of 3D low-frequency seismic data from a West-Siberian reservoir produced an accurate delineation of the fracturedhydrocarbon-bearing zones. P-wave propagation, reflection and transmission at an impermeable interface between elastic and dual-porosity poroelastic media is investigated. It is obtained that the reflection and transmission coefficients are functions of the frequency. At low frequencies, their frequency-dependent components are asymptotically proportional to the square root of the product of frequency reservoir fluid mobility and fluid density.