Foundation of Ultradeep Boundary Detection Based on the Electric Field Characteristics

An ultradeep boundary detection method based on the characteristics of the electric field in a single well is proposed. Unlike any conventional azimuthal electromagnetic (EM) wave logging approach, the new design employs an open-loop half-circle antenna other than the tilted or transverse closed-loop coil antenna as the receiver. The voltage on the half-circle antenna varies periodically with the tool-face angle, which provides the azimuthal information of the boundary. To explore how this new measuring method works, we investigate the electric field characteristics around the receiving antenna. The voltage is calculated by the integral of the electric field. By analyzing the voltages on each segment and their serial connection, the reason is revealed for the significantly enhanced voltage on the half-circle antenna compared to the tilted/transverse closed-loop coil. It lays a new foundation of ultradeep boundary detection based on the electric field characteristic. The voltage response behaviors are further investigated with respect to the tool offset, frequency, distance to the boundary (DTB), and conductivity anomaly. The monotonous changing of the voltage is observed within a wide range of those parameters. The results show that the half-circle antenna has great potential in realizing ultradeep boundary detection with a small offset.