1. n. [Formation Evaluation, Geophysics]
A survey technique that measures the seismic signal transmitted from a source, located in one well, to a receiver array in a neighboring well. The resulting data are processed to create a reflection image or to map the acoustic velocity or other properties (velocities of P- and S-waves, for example) of the area between wells. Placement of the source and receiver array in adjacent wells not only enables the formation between wells to be surveyed, it also avoids seismic signal propagation through attenuative near-surface formations. Another advantage is that it places the source and receiver near the reservoir zone of interest, thereby obtaining better resolution than is possible with conventional surface seismic surveys. This technique is often used for high-resolution reservoir characterization when surface seismic or vertical seismic profile (VSP) data lack resolution, or for time-lapse monitoring of fluid movements in the reservoir.