Time-domain broadband dielectric logging
Described are tools, systems, and methods for dielectric logging using transient waveforms. In some embodiments, one or more microstrip antennas are employed for the measurements. In various embodiments, the waveforms are processed in the time-domain to determine the dielectric properties of a formation, from which geophysical formation properties can then be derived. Further embodiments are disclosed.
1. A method comprising:
disposing a dielectric logging tool in a borehole to place one or more antennas of the dielectric logging tool adjacent to a formation surrounding the borehole;
using the dielectric logging tool to
generate a first transient waveform and transmit the first transient waveform via transmission line to at least one antenna of the one or more antennas, and
measure at least one second transient waveform received via transmission line, in response to transmission of the first transient waveform, from at least one of the one or more antennas;
performing time-domain analysis of the first and the at least one second transient waveforms to determine at least one electric response parameter of the at least one of the one or more antennas based on the first transient waveform and the at least one second transient waveform; and
determining, based on the at least one electric response parameter, at least one dielectric property of the formation.
2. The method of claim 1 , wherein the first transient waveform is transmitted to an antenna that is capacitively or galvanically coupled to the formation.
3. The method of claim 1 , wherein the first transient waveform is transmitted to a microstrip antenna.
4. The method of claim 1 , wherein the at least one second transient waveform comprises a waveform reflected at the at least one antenna to which the first transient waveform was transmitted.
5. The method of claim 1 , further comprising:
using inversion to adjust one or more dielectric parameters in a computational model of the formation, and
wherein the inversion is based on at least one of
time-domain data samples selected from the measured at least one second transient waveform and a transient waveform computed based on the first transient waveform in conjunction with the computational model of the formation and
a time-frequency map obtained from the measured at least one second transient waveform by short-time frequency transform.
6. The method of claim 1 , wherein the at least one dielectric property comprises at least one of a resistivity or a dielectric constant.
7. The method of claim 1 , further comprising determining a geophysical property of the formation from the at least one dielectric property using a rock physics model.
8. The method of claim 1 ,
further comprising:
generating and transmitting first transient waveforms and receiving second transient waveforms for a plurality of depths along the borehole, wherein the dielectric logging tool comprises a plurality of antennas mounted at different azimuthal positions about an axis of a wireline tool body;
creating a log of the at least one dielectric property of the formation across the plurality of depths based on the first and the at least one second transient waveforms; and
generating a dielectric image of the formation based on an analysis of the first and the at least one second transient waveforms.
9. The method of claim 1 , wherein the one or more antennas are mounted on a rotating bottom hole assembly, the method further comprising generating a dielectric image of the formation based on the time-domain analysis of the first and second transient waveforms for a plurality of azimuthal positions.
10. The method of claim 1 , wherein the at least one electric response parameter of the at least one of the one or more antennas comprises at least one of an impedance and a scattering parameter.
11. The method of claim 1 , wherein performing time-domain analysis of the first and second transient waveforms to determine at least one electric response parameter of the at least one of the one or more antennas based on the first transient waveform and the second transient waveform comprises performing time-frequency analysis of the first and second transient waveforms.
12. A system comprising:
a dielectric logging tool comprising:
one or more antennas; and
one or more transmission lines connected, at respective first ends thereof, to the one or more antennas;
a processor; and
a machine-readable medium having program code executable by the processor to cause
the system to perform operations comprising:
generate a first transient waveform for transmission to at least one of the one or more antennas;
measure at least one second transient waveform that is received from at least one of the one or more antennas in response to transmission of the first transient waveform; and
analyze, using a time-domain analysis, the first and the at least one second transient waveform to determine at least one electric response parameter of the at least one of the one or more antennas;
based on the at least one electric response parameter, determine at least one dielectric property of a formation in which the one or more antennas are disposed.
13. The system of claim 12 , wherein the dielectric logging tool is at least one of a wireline logging tool and a sub within a bottom hole assembly.
14. The system of claim 12 , wherein the one or more antennas are disposed at different azimuthal positions about an axis of the dielectric logging tool.
15. The system of claim 12 , wherein at least one antenna of the one or more antennas is aligned azimuthally and at least one antenna of the one or more antennas is aligned vertically within the dielectric logging tool.
16. The system of claim 12 , wherein at least one of the one or more antennas comprises a microstrip antenna.
17. The system of claim 12 , wherein at least one of the one or more antennas is configured, based on an expected value of the at least one dielectric property of the formation, to have a resonance frequency to detect changes in the at least one dielectric property of the formation.
18. The system of claim 12 , wherein the one or more antennas comprises a plurality of microstrip antennas, wherein each microstrip antenna of the plurality of microstrip antennas is configured to have a unique resonance frequency.
19. The system of claim 12 ,
wherein the operations comprise:
adjust one or more dielectric parameters in a computational model of the formation based on the first and second transient waveforms.
20. A dielectric logging tool comprising:
a tool body for deployment in a borehole;
mounted on the tool body, one or more microstrip antennas for disposal adjacent to a formation to be characterized;
one or more transmission lines connected, at respective first ends thereof, to the one or more antennas;
a source configured to generate a first transient waveform for transmission to the one or more antennas via the one or more transmission lines; and
a receiver to receive and measure a second transient waveforms that is transmitted from the one or more antennas via the one or more transmission lines, wherein the second transient waveform is generated in response to transmission of the first transient waveform.