Measurement of seismic structure at scales below «20m (the resolution limit of surfacegenerated seismic waves) requires borehole seismic sources and receivers. For borehole seismic data analysis, typical seismic imaging using plane wave propagation in 1-D layering must be supplanted by spherical wave propagation in 3 dimensions. Images of production fronts and discrete rock units must be sought as coherent scattering in a background of incoherent scattering by random discontinuities. The spectrum of scattered waves measures the density and size of the velocity fluctuations; as velocity fluctuations are often due to changing porosity and fracture density, broadband borehole seismic scattering spectra can characterize these features of reservoir volumes in the sub-metre to multi-metre range.

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