Single-well imaging (SWI) is a borehole measurement technique aimed at detecting geologic interfaces or structures tens of meters away from the borehole. In SWI, acoustic signals generated by a monopole or a dipole source in the borehole are reflected by geologic interfaces and received by arrays of receivers of the same type. Current SWI cannot determine the azimuth angle of the geologic interfaces uniquely. We have developed a new SWI system with combined dipole and monopole receivers for a dipole source. This system can be used to determine the azimuth angle uniquely. The other difficult issue is to quickly simulate the wavefield of SWI to meet the needs of real-time data processing in field logging. We derive asymptotic solutions of the horizontal displacement and the fluid pressure for the reflected wave from the geologic interfaces in this nonaxisymmetric system. The radiation fields of a monopole and a dipole are computed using the steepest-descent integration method. The wave reflected from a reflector outside the borehole is proved to be equivalent to the radiation of a virtual source outside the borehole. We use the reciprocity relation between the virtual source and a monopole or a dipole source to obtain the asymptotic solutions of fluid pressure or horizontal displacement for the reflected wave. The asymptotic results agree well with those from 3D finite-difference simulation. The asymptotic solution demonstrates the polarity of fluid pressure changes when the azimuth angle changes by 180°. Based on the characteristics of asymptotic solutions, we evaluate a scheme to determine the azimuth uniquely.

An experimental system is built for the electrokinetic measurements with a small scaled seismoelectric detector and a high resolution digitizer (1 MS s^–1, 22 bits). The acoustic and seismoelectric experiments are carried out in different borehole models at the high frequency of 90 kHz in the laboratory. All the localized seismoelectric signals that accompany compressional wave, shear wave and Stoneley wave are first clearly observed with a monopole source in sandstone boreholes that are saturated by tap water. The amplitudes of these signals are measured in the range of 1–120 μV, which is useful for designing the seismoelectric logging instruments. Then the amplitude ratio of electric signal to acoustic pressure (REP) for each of the three waves is calculated and compared with the theoretical simulations. Based on the experimental data, we find that seismoelectric logging signals as well as REP become stronger at the more permeable borehole model. We also find that seismoelectric logging signals are more sensitive to permeability and porosity compared with acoustic logging signals. Therefore, this study verifies the feasibility of seismoelectric well logging, and further indicates that the seismoelectric logging technique might be a preferable method to estimate formation parameters in the field measurements.