Numerical simulation of radiation, reflection and reception of elastic waves from a borehole dipole source

A recent advance in single-well reflection imaging is the utilization of a dipole acoustic system in a borehole to radiate and receive elastic waves to and from a remote geological reflector in formation. This paper substantiates this dipole-acoustic imaging technology by numerically simulating the radiation and reflection of the wavefield generated by the borehole dipole source and analyzing the receiving sensitivity of the dipole system to the incoming reflection waves. The analyses show that a borehole dipole source can radiate a compressional wave (P wave) and two types of shear waves (i.e., SV and SH waves) into the formation. The SH wave has wide radiation coverage and the best receiving sensitivity, and is most suitable for dipole-shear imaging. In an acoustically slow formation the dipole-generated P wave has strong receiving sensitivity and can also be utilized for reflection imaging. An important feature of dipole imaging is its sensitivity to reflector azimuth, which results from the directivity of the dipole source. By using a four-component data acquisition method to record the dipole-generated reflection signal, the reflector azimuth can be determined. The numerical simulation results provide a solid foundation for the dipole acoustic imaging technology.