Detection Of Subsurface Fractures And Permeable Zones By The Analysis Of Tube Waves

Abstract

In Vertical Seismic Profiling tube waves are generated by compressional waves impinging on subsurface fractures or permeable zones. The amplitude of tube waves is dependent upon the formation permeability, the length of the fracture, and on the source frequency. The generation of tube waves is formulated theoretically and the relative effects of these parameters are studied individually. Field examples are shown for open fractures in granite. From tube wave amplitudes normalized to P-wave amplitudes, calculated permeabilities are on the order of 400 millidarcys.