Method and Apparatus for Looking Ahead of the Drill Bit

A plane wave generator (PWG) tool for looking ahead of a drill bit, comprising

• a casing that is adapted to be suspended downhole inside a wellbore from an uphole side of the casing by a wireline configured to supply electric power to the PWG tool and to transmit reflection data generated by the PWG tool to a surface control system;
• a PWG system housed in the casing, wherein the PWG system includes a beam forming network (BFN) architecture and a plurality of antenna elements mounted to a base of the PWG system so that the plurality of antenna elements mounted to the base are exposed on a downhole side of the casing that is opposite to the uphole side,
• wherein the base is a cylindrical base and a space between the plurality of antenna elements on the base is filled with microwave absorbent material,
• wherein the plurality of antenna elements are mounted to the cylindrical base as a circular array of a plurality of concentric rings of antenna elements, each of the plurality of concentric rings including at least one of the plurality of antenna elements, and
• wherein the BFN architecture is configured to individually control relative amplitude and phase weights between the plurality of concentric rings of antenna elements, while exciting each antenna element within the same concentric ring with the same amplitude and phase.

A method for looking ahead of a drill bit, comprising:

• pulling a drill bit and a drill string out of a borehole in response to determining a need to look ahead of the drill bit during a drilling operation;
• lowering a wireline based plane wave generator (PWG) tool downhole into the borehole such that a bottom surface of the PWG tool is positioned at a predetermined height above a bottomhole surface of the borehole, wherein the PWG tool includes a plurality of antenna elements that are mounted to the bottom surface of the PWG tool and that are configured to transmit and receive electromagnetic signals;
• transmitting electric power from a surface based power source to the plurality of antenna elements of the PWG tool via the wireline;
• emitting electromagnetic signals from the plurality of radiating elements in response to the transmitted electric power such that the emitted electromagnetic signals:
• (i) are synthesized into plane waves in a quiet zone having a finite volume and being in close proximity to the plurality of antenna elements, and (ii) penetrate a subsurface rock formation beyond the bottomhole surface of the borehole as the plane waves;
• receiving, with the plurality of antenna elements and in response to the emitted electromagnetic signals, reflections of the transmitted plane waves from the subsurface rock formation in the quiet zone to capture reflection coefficients in frequency or time domain of different media of the subsurface rock formation in the quiet zone;
• generating reflection data based on the received reflections of the transmitted plane waves, wherein the reflection data indicates a contrast in electromagnetic properties at an interface between two different media of the subsurface rock formation in the quiet zone;
• transmitting the reflection data to the surface control system via the wireline;
• and
• processing, at the surface control system, the reflection data for permittivity prediction and generation of image data, wherein a lost circulation zone in the quiet zone is detected based on the generated image data.