Laboratory experimental studies of seismic scattering from fractures

Laboratory acoustic measurements are performed with Lucite fracture models to understand the scattering characteristics of a seismic wave in a fracture zone. The fracture models include single, dual, and multiple fracture zones with varying fracture apertures, height, and spacing. Fractures are created by both very fine saw cuts and laser-etching. A vertical P-wave source is used with vertical (P) and horizontal (S) receivers to measure the reflected and scattered wavefield as a function of offset and azimuth relative to the fracture orientation. The amplitude of the arrival generated from the fracture tips is proportional to the fracture aperture. Comparison of traces from a single fracture and a dual fracture model indicates that multiple scattering is an important component of the scattered wave signal in fracture systems. In the fracture zone models, the PP and PS scattered wave energy varies azimuthally providing multiple methods for fracture orientation estimation. In particular, PS scattering on the transverse component is a maximum at 45°, while the PS inline component shows a systematic increase in amplitude as the azimuth approaches 90°. Total scattered wave energy is also observed to vary with changes in fracture aperture and height providing a possible means to estimate fracture zone flow capacity from seismic data.