Microstrip antenna-based logging tool and method
A dielectric logging tool for use in a borehole that penetrates a subsurface formation, includes: at least one wall-contacting face with one or more embedded microstrip antennas including a transmit antenna; an oscillator that supplies a transmit signal; a coherent receiver that measures the one or more scattering coefficients; and a processor that derives a formation property from the one or more scattering coefficients. The tool may be conveyed along a borehole, with the scattering coefficients and derived formation property values associated with tool position and orientation to provide a permittivity log.
1. A logging tool for use in a borehole that penetrates a subsurface formation, the tool comprising:
at least one wall-contacting face that includes:
a substrate layer disposed on the at least one wall-contact face;
a coating layer disposed on the substrate layer, wherein the coating layer is a polytetrafluoroethylene, a chemically-inert layer, a non-conductive layer, a ceramic, or an alumina;
one or more microstrip antennas disposed on the coating layer, the one or more microstrip antennas including a transmit antenna; and
a protective layer disposed over the one or more microstrip antennas and the coating layer, wherein the protective layer is a second ceramic, a polymer, or a carbon fiber resin;
an oscillator coupled to the transmit antenna to supply a transmit signal;
a coherent receiver coupled to the one or more microstrip antennas to measure one or more scattering coefficients;
a directional coupler that is connected to the one or more microstrip antennas and the coherent receiver; and
a processing unit coupled to the coherent receiver to derive a formation property from the one or more scattering coefficients.
2. The tool of claim 1 , wherein the formation property includes complex permittivity.
3. The tool of claim 1 , wherein the one or more microstrip antennas further include at least two receive antennas.
4. The tool of claim 1 , wherein the processing unit is downhole and stores the formation property in a downhole memory.
5. The tool of claim 1 , wherein the processing unit is coupled to a surface interface to receive the one or more scattering coefficients via a wired or wireless link.
6. The tool of claim 1 , wherein the at least one wall-contacting face is part of a sensing pad biased against a borehole wall by a wireline tool.
7. The tool of claim 6 , wherein the wireline tool includes multiple sensing pads, each having a wall-contacting face with one or more microstrip antennas.
8. The tool of claim 1 , wherein the at least one wall-contacting face is part of a stabilizer fin.
9. The tool of claim 1 , wherein the coherent receiver measures the scattering coefficients at multiple frequencies.
10. The tool of claim 9 , wherein the transmit signal is a frequency-swept signal that ranges from below 10 MHz to over 1 GHz.
11. The tool of claim 1 , wherein the coherent receiver is further coupled to measure the transmit signal.
12. A logging method that comprises:
moving a logging tool along a borehole, wherein the logging tool includes:
at least one wall-contacting face that includes:
a substrate layer disposed on the at least one wall-contact face;
a coating layer disposed on the substrate layer, wherein the coating layer is a polytetrafluoroethylene, a chemically-inert layer, a non-conductive layer, a ceramic, or an alumina;
one or more microstrip antennas disposed on the coating layer, the one or more microstrip antennas including a transmit antenna; and
a protective layer disposed over the one or more microstrip antennas and the coating layer, wherein the protective layer is a second ceramic, a polymer, or a carbon fiber
measuring one or more scattering coefficients of the one or more microstrip antennas;
determining formation values based at least in part on the one or more scattering coefficients; and
associating the formation values with tool position to provide a log.
13. The method of claim 12 , wherein the log is a permittivity log.
14. The method of claim 12 , further comprising:
storing the log on anon-transient information storage medium; and
displaying a visual representation of the log for use in identifying a completion zone.
15. The method of claim 12 , wherein the one or more microstrip antennas include at least one transmit antenna and at least two receive antennas, and wherein said measuring includes measuring S 11 , S 12 , and S 13 .
16. The method of claim 12 , wherein said measuring includes measuring a phase of the one or more scattering coefficients.
17. The method of claim 12 , wherein said determining includes inverting for formation resistivity, size of a standoff gap, and permittivity of fluid in the standoff gap.
18. The method of claim 12 , wherein the logging tool is a wireline logging tool with a sensing pad having the wall-contacting face.
19. The method of claim 12 , wherein the logging tool is a logging while drilling tool with a stabilizer fin having the wall-contacting face.
20. The method of claim 12 , wherein said measuring includes detecting a frequency dependence of the one or more scattering coefficient.