Off-center Monopole and Dipole Sources in Fluid-filled Boreholes

A variety of seismic testing techniques rely on the use of seismic sources, detectors, or both, placed at some depth below the ground surface; these are often installed within fluid-filled boreholes. The interpretation of the records obtained in the course of such explorations requires a thorough understanding of how waves propagate in the borehole and its immediate vicinity. Depending on the distance between the source and the receiver as well as their placement and orientation relative to the axis of the borehole, it is known that very complex wave patterns may arise. In this paper, analytical-numerical solutions are used to study the wave-field elicited by monopole or dipole sources within a fluid-filled cylindrical cavity drilled through an unbounded homogeneous elastic medium. This model is used to assess the effects of a source-receiver tool, placed in an offcentered and/or tilted position inside the fluid-filled borehole, on the propagation of both axisymmetric and non-axisymmetric wave modes.